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  • #46
    Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

    Originally posted by cpw View Post
    And to get things totally off topic, my oil fired heater has a recovery of ~200 Gallons an hour. The 40 gallon tank was just not enough for our large tub, so we upgraded to an 80. Until heating oil is $9 a gallon, we'll come out ahead of electric (assuming electric doesn't go more than $.25/kWH).
    If you don't mind the question, how much is oil today and what are you paying for electric? Does your area have gas service and if so, how does that compare? Although that 80 gal with the huge recovery must mean you never run short of hot water.

    Comment


    • #47
      Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

      Originally posted by Andy_M View Post
      If you don't mind the question, how much is oil today and what are you paying for electric? Does your area have gas service and if so, how does that compare? Although that 80 gal with the huge recovery must mean you never run short of hot water.
      We don't have gas service where I am, so I don't know how much it is. Other neighborhoods have it, just not mine.

      Oil is about $4.49 right now, electric is around $0.20/kWH. Depending on the month there is a delivery charge of 9.468 or 8.220 cents, then there is a supply charge with varies, but is also around 10 cents, I don't have a bill handy so can't find the exact cost, but it does vary, with some months being a total of almost $0.25/kWH.

      Comment


      • #48
        Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

        We have one natural gas company and the farther you are away from the city the more gas costs you per Cubic ft. They will flat out rob me if i wanted gas......but unless I was going tankless it not even a consideration. Being Total electric my power bill is about 150 a month in the winter and 260 in the summer and I keep my house at 68-74 degrees year round. In my previous house over 11 years ago I was only using gas in the summer to heat water and in the winter I used gas to heat water and the HVAC system.......my gas bill in the summer was about 50-65.00. Now compare 60.00 to heat only my water to an electric bill 12 yrs later for the whole house including HVAC heat for 150-200 a month with electricity. Gas sucks!!!!

        Natural gas is no bargain here...... Tho thats what the gas company wants people to think.
        Last edited by TheMaster; 04-22-2011, 01:59 PM.

        Comment


        • #49
          Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

          Originally posted by Andy_M View Post
          I do that, without the cold shower, to lobsters.

          As for the measurements... yeah right. I would want to do that so we could continue this incredibly rewarding and illuminating discussion still longer?

          I don't think so.

          But if you insist, My consulting rate is $135/hr, 40 hour minimum, 50% payable in advance.

          You should be paying me...you learned that 1st hr rating doesn't mean crap when your trying to fill a big tub. why do you think tankless heaters are popular with people who fill jetted tubs larger than a standard bathtub or with people who have a few kids. because they need alot of water at once...not over an hrs time.

          Its ok tho...I realize your college educated and that means your smart and plumbers are not so educated.

          Comment


          • #50
            Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

            Originally posted by TheMaster View Post
            You should be paying me...you learned that 1st hr rating doesn't mean crap when your trying to fill a big tub. why do you think tankless heaters are popular with people who fill jetted tubs larger than a standard bathtub or with people who have a few kids. because they need alot of water at once...not over an hrs time.
            Sorry to burst your bubble but unfortunately, while many here have taught me quite a lot, I didn't learn diddley from you. Except that you don't understand condensation, you don't ask any questions before making recommendations, and it drives you crazy when someone doesn't defer to your "expertise" and disagrees with your views.

            Sure a huge tub or ultra high-flow shower creates a lot of demand. Who's arguing against that? The point in THIS discussion, which you don't seem to get, is that OP doesn't have that situation. He has two people with a 60 gallon tub and pretty standard everything else. I have told you that I fill my large 6 foot soaking tub with a 40 gallon gas and have had no problem. I have told you that Kohler recommends that the tank be 70% of the tub capacity, which would be a 42 gallon tank for OP's tub. I have therefore suggested that a 50 gal gas with large burner would fill the tub just fine, have some extra capacity compared to Kohler's minimum recomendation, and provide good fast recovery.

            You dont' care, you're just obsessed with defending your argument. You can hold that opinion, it's fine. I can disagree. I've stated my reasons, and you've said why you don't like them. You've stated yours, and I've said why I dislike them. There is no need to go on and on and on about it.

            Originally posted by TheMaster View Post
            Its ok tho...I realize your college educated and that means your smart and plumbers are not so educated.
            Now, smiley faces aside, you really should be ashamed of yourself for that comment. It speaks volumes about your own insecurity. The value of anyone's argument always needs to stands on its own merit.

            Regarding your gas costs: If your gas rates aren't favorable, that's an exception, not the rule, and thus doesn't have much to do with anyone else. For the bulk of the country where gas service is available, gas is way cheaper than electric. Want to keep arguing? Then argue with the applicance manufacturers and the EPA, both of whom project costs of operation of water heaters in both gas and electric. Those poor college schmucks think gas is a lot cheaper, too.

            Oddly, though, I logged on this evening because I've been busy today, but saw your comment before I left on the cost of the twin 40s compared to the gas 50 and wanted to say that it was the first argument you've made on this subject that actually *nearly* made some sense to me and didn't involve a load of arm-waving.

            I say "nearly" because you have to look not just at the cost of the water heaters, but at the total cost of the installation, including the electric swervice that may need to be installed (OP is replacing a gas heater) Then you need to compare that to the cost of the gas installation, which from OPs information sounds like it will involve a substantialk vent installation. Then, and I risk sounding like I've been to college, you need to look at the energy costs for the two alternatives over their projected lifespan and convert them to present value, at a reasonable discount rate. Why? Because that's how you do a financial analysis.

            But still, you came up with a valid fact that's actually relevant to the discussion, and I think that's great.

            In my case, though, I would still not even consider electrics because here in CA, the cost advantage for gas is overwhelming. But for someone in a place like the one you're in, where gas is high relative to electric, your point is a valid one. If the costs of installation and operation work out, and the installation is practical then it your dual 40s would definitely be worth looking at. I wouldn't go with the bottom end 6 year units, though. I think there are probably reasons why they're so cheap. I would pay more and get 9 or 12 year heaters, but that's just my preference.

            I'm way tired of this thread. Keep arguing if you like, but I'm out.

            Comment


            • #51
              Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

              hot water heater
              Ideal Plumbing

              Comment


              • #52
                Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                Originally posted by Andy_M View Post
                Sorry to burst your bubble but unfortunately, while many here have taught me quite a lot, I didn't learn diddley from you. Except that you don't understand condensation, you don't ask any questions before making recommendations, and it drives you crazy when someone doesn't defer to your "expertise" and disagrees with your views.

                Sure a huge tub or ultra high-flow shower creates a lot of demand. Who's arguing against that? The point in THIS discussion, which you don't seem to get, is that OP doesn't have that situation. He has two people with a 60 gallon tub and pretty standard everything else. I have told you that I fill my large 6 foot soaking tub with a 40 gallon gas and have had no problem. I have told you that Kohler recommends that the tank be 70% of the tub capacity, which would be a 42 gallon tank for OP's tub. I have therefore suggested that a 50 gal gas with large burner would fill the tub just fine, have some extra capacity compared to Kohler's minimum recomendation, and provide good fast recovery.

                You dont' care, you're just obsessed with defending your argument. You can hold that opinion, it's fine. I can disagree. I've stated my reasons, and you've said why you don't like them. You've stated yours, and I've said why I dislike them. There is no need to go on and on and on about it.



                Now, smiley faces aside, you really should be ashamed of yourself for that comment. It speaks volumes about your own insecurity. The value of anyone's argument always needs to stands on its own merit.

                Regarding your gas costs: If your gas rates aren't favorable, that's an exception, not the rule, and thus doesn't have much to do with anyone else. For the bulk of the country where gas service is available, gas is way cheaper than electric. Want to keep arguing? Then argue with the applicance manufacturers and the EPA, both of whom project costs of operation of water heaters in both gas and electric. Those poor college schmucks think gas is a lot cheaper, too.

                Oddly, though, I logged on this evening because I've been busy today, but saw your comment before I left on the cost of the twin 40s compared to the gas 50 and wanted to say that it was the first argument you've made on this subject that actually *nearly* made some sense to me and didn't involve a load of arm-waving.

                I say "nearly" because you have to look not just at the cost of the water heaters, but at the total cost of the installation, including the electric swervice that may need to be installed (OP is replacing a gas heater) Then you need to compare that to the cost of the gas installation, which from OPs information sounds like it will involve a substantialk vent installation. Then, and I risk sounding like I've been to college, you need to look at the energy costs for the two alternatives over their projected lifespan and convert them to present value, at a reasonable discount rate. Why? Because that's how you do a financial analysis.

                But still, you came up with a valid fact that's actually relevant to the discussion, and I think that's great.

                In my case, though, I would still not even consider electrics because here in CA, the cost advantage for gas is overwhelming. But for someone in a place like the one you're in, where gas is high relative to electric, your point is a valid one. If the costs of installation and operation work out, and the installation is practical then it your dual 40s would definitely be worth looking at. I wouldn't go with the bottom end 6 year units, though. I think there are probably reasons why they're so cheap. I would pay more and get 9 or 12 year heaters, but that's just my preference.

                I'm way tired of this thread. Keep arguing if you like, but I'm out.
                Heres the bottom line. If your filling your tub with a 40 gal water heater its above the 120 degree recommended temp setting. Simple as that.

                The original poster has a tub with a 60 gal fill capacity. The water heater must be able to deliver 70% of this capacity at the THERMOSTAT setting. 70% of 60 gal is 42 gallons. A 50 gal water heater that can deliver 70% of its capcity will only deliver 35 gallons at the thermostat setting.

                With the temp set at 120 degrees you cant fill a 60 gal tub with a 50 gal heater to a comfortable bath temp. So that tells me your recommending the original poster use a smaller than necessary water heater and crank the temp up as to reduce the ratio of the hot mix to arrive at the target bath temp of 105-110 so the bath doesn't cool off before the tubs full.

                Kohler says the water heater must be 70% of the tubs fill capacity. Whys that? I've told you....the avrage tank type water heater can only supply 70% of its thermostat setting in one draw. For a 50 gal water heater that would be 35 gallons.

                Your not taking into account the incoming water temp either...the original poster lives in the NORTH with cold incoming water temps.

                Here is the formula for calculating what percent of a particular draw is hot water....such as filling a bathtub.

                target bath temp minus incoming water temp
                _______________________________________
                Thermostat setting temp minus incoming water temp

                105 target temp minus 60 degree incoming water temp= 45
                120 thermostat temp minus 60 degree incoming water temp=60

                45 divided by 60 = .75 or 75%

                Now lets take 75% of the 60 gal tub capacity..= 45 gallons


                So that tells you that it takes 45 gallons of 120 degree water mixed with 15 gallons of cold water to have 60 gallons of tempered water @ the target bath temp of 105 degrees.

                Now how much will a 50 gal water heater deliver???? We said 70% correct? Whats 70% of 50 gal??? Its 35 gallons. Our calculations indicate we need a minimum of 45 gallons.......proving a 50 gal gas cannot provide the volume at a recommended setting of 120 degrees.

                Now that I proved that.....I will refer you to Rheems website and there you can search and find information about water heaters and condensation. All water heaters have a degree of condensation by the nature of the appliance. What does Rheem say about the cause of excessive condensation???? THE MAIN CAUSE IS AN UNDERSIZED WATER HEATER.

                Having a high thermostat setting increases the standby heat loss and the hotter the water the more corrosive it is...reducing tank life and wasting energy.

                ADD> I'm not arguing...I'm providing facts from Rheem. What are you doing other than giving your opinion? This section of the forum is "ASK THE PLUMBING EXPERTS" DO you think your a plumbing expert???????? IMO your not.
                Last edited by TheMaster; 04-23-2011, 09:05 AM. Reason: ADD> THE FACTS

                Comment


                • #53
                  Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                  Also by you cranking the temp up on the 50 gal gas(which will be done to meet demand in your scenario and leaving an unsafe operating condition) you are wasting alot of energy keeping that water hot and burning a pilot....the energy label of estimated cost to operarte goes out the window when you crank the temps up past the recommended setting...so your not offering an apples to apples comparison.

                  There is NO difference between a 6 yr tank and a 12 year tank. Now they may add an extra anode rod to the tank but the TANK is the same....some manufacturers dont even do that....its the same tank and your paying for an extended warranty is all. See you learned somthing else.

                  ADD>


                  Here is another example using a 40 gal water heater like Andy_M says he has and fills a 6' tub. Since Andy_M charges $145.00 an hr to talk to me I will hafta guess at all the other inputs into the equation but I have asked. Now lets say we have a target bath temp of 100 degrees(thats warm to me not hot) and a tub that has a 60 gal fill and the incoming water temp is a generous 75 degrees YEAR ROUND and a thermostat setting of 140 degrees.

                  100 degrees minus 75 degrees = 25
                  140 degrees minus 75 degrees = 65

                  25 divided by 65 = .3846...lets call it 38%
                  So 38% of the water that fills the tub will be hot water.

                  The typical 40 gal gas is capable of delivering 70% of its capacity at the thermostat setting. Thats 28 gallons.

                  The tub has a fill capacity of 60 gallons and with our input numbers 38% of that will be 140 degrees given or incoming water temp of 75 degrees to get tempered water of 100 degrees.

                  38% of 60 gal = 22.80 gal. leaving 5.20 gal of available target temp water

                  A 50 gal would leave 12.20 gal availble at target temp

                  80 gal would leave 33.20 gal available at target temp

                  Even a small 30 gal would only come up short by 1.80 gallons.......but your answer to that would be just turn the water temp up until it meets demand...problems solved.

                  This info was copied straight from RHEEM....both of our favorite water heaters. Maybe they dont understand the relationship between condensation and water heaters as well as you do.....maybe they didn't go to college either.
                  __________________________________________________ __________________________________________________ ___

                  What fools many homeowners and servicemen? Condensation. Condensation is the result of
                  the reduction of temperature by the removal of latent heat of evaporation. The liquid product being produced is
                  known as condensate. The removal of heat shrinks the volume of the vapor and the loss of energy will lead to the
                  transformation of the gas into a liquid condensate.
                  We have all seen the condensate that forms on a glass of ice water on a hot humid day. Similar to when the
                  first tank of cold water is heated, the same condensation can develop when a water heater is undersized or
                  overdrawn. The thermostat brings on the main burner to heat the cold water that has entered the tank. If the water
                  heater is large enough, the water temperature in the tank will not drop to the point where it cools the flue gasses to
                  the point of condensation.

                  Interestingly, the majority of ‘nonleaker’ returns are found to have been replaced during the winter and
                  early spring months when incoming water temperatures are at their lowest. Cold water inlet temperatures can vary
                  in excess of 30
                  ° F between seasons.

                  Water vapor is one of the chief by-products of the combustion of gas. A gas water heater burning 50,000
                  BTU per hour produces almost five pounds of water vapor in one hour of continuous heating. If allowed to cool and
                  condense fully, the five pounds of water vapor would form more than two quarts of water. Good venting is essential
                  to the operation of a gas water heater. Venting carries away the products of combustion that could contaminate the
                  air in a home and carries away the water vapor. A water heater must be of sufficient size to meet the homeowners
                  demands for hot water. Homeowners will over draw an undersized water heater to the extent that the tank is
                  constantly heating and cooling. Recall our glass of ice water? The same thing happens on the outside of the heater
                  tank. The condensation rolls down the side of the tank and collects in the drain pan. Looks like a leaker, but is really
                  condensation.
                  While all water heaters have some degree of condensation, excessive moisture on the outside of the tank
                  can cause pilot outage and premature tank failure. Pilot outage can occur due to the condensate running down the
                  inside of the flue tube onto the main burner and extinguishing the pilot flame. Premature exterior corrosion of the
                  water heater tank, corrosion of the inside of the flue tubes and rusting on the main burner assembly are some of the
                  problems caused by excessive condensation.
                  __________________________________________________ __________________________________________________ ___________




                  Last edited by TheMaster; 04-23-2011, 10:52 AM.

                  Comment


                  • #54
                    Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                    I know that I said I was done with this thread. But you can’t let it drop, can you? So here is the last thing (really) that I’m going to offer on this topic. You might find it interesting, if you can get past your need to be the all-knowing expert.

                    First of all, you made a stink about me having to run my 40 gal heater above 120F. Duh. I said I was doing this all along. Moreover, I said, and believe, that OP would have to run the 50 gal gas WH above 120 as well. Read the posts.

                    It occurred to me that it’s doubtful if you could fill a 60 gal tub to a reasonable temperature even with your 40 gal electrics set at 120 *at the WH* as you claim. That’s to low of a temperature in general, leading to too-low temps at the faucets in the house. I think 120 is a good temp AT THE TAP. But it’s not a disaster to have it set a little higher. In fact, for older dishwashers without booster heaters you need the water temp – at the dishwasher - to be above 130 or even 140 to get good performance. Some recommend that the water heater temp should be at 130 or above for bacteria control reasons, although I’m not a biologist (you, being an expert and master, probably are… since you apparently know everything) and thus can’t say either way. But some do favor such high temps.

                    As I said long ago, I do have my little 40 gal turned up all the way, whatever that is, and it’s been doing fine out in the garage since 1995. So running the tank a little higher isn’t a guarantee of short lifetimes. Steel and glass tanks don’t really care about 120 versus 130 or 140, and the gas burner doesn’t even know that the water temp is.

                    In any case, and even though you are an expert and prefer to play with your “rule of thumb” numbers, I am not an expert and need to do a little real analysis to get a better idea of what is really happening with dual 40 gal electrics and 50 gal gas water heaters when it comes to filling a 60 gal tub. It’s not too time consuming, and since you don’t like my rates ($135, btw, not $145 -- but for you, I would only charge $155), I did it just for fun.

                    Here’s the parameters I used:

                    DUAL ELECTRIC WATER HEATERS (Master’s expert, never-been-wrong proposal)

                    Tank capacity = 2 x 40 gal = 80 gal
                    Burner = 2 x 4500W, simultaneous operation (30717 BTU)
                    Tub fill size = 60 gal (assume this is actual fill, not overflow capacity)
                    Main supply temp = 55F
                    Tank T-stat temp = 120
                    T-stat deadband = 7F
                    Temp loss in pipe from WH to tub fill valve = 5F (assume new install very good insulation)
                    Tub fill valve flow rate = 4 gpm
                    Energy factor = .92

                    GAS WATER HEATER (andy_m’s lowly, non-expert opinion)

                    Tank capacity = 50 gal
                    Burner = single 40,000 BTU/hour
                    Tub fill size = 60 gal (assume this is actual fill, not overflow capacity)
                    Main supply temp = 55F
                    Tank T-stat temp = 130
                    T-stat deadband = 7F
                    Temp loss in pipe from WH to tub fill valve = 5F (assume new install very good insulation)
                    Tub fill valve flow rate = 4 gpm
                    Energy factor = .62

                    Here are the results:

                    Temp of tub filled with water, neglecting cool-down losses:

                    Electric system: 98.8F Gas system: 98.1F DIFFERENCE: 0.7F

                    Temp of the water in the tank right after fill:

                    Electric system: 92.3F Gas system: 85.8F DIFFERENCE: 6.7F

                    In other words, there isn’t a hill of beans worth of difference at the tub. Neither is really hot, so I hope OP’s tub has an internal heater.

                    Not surprisingly, the electric system has more, hotter water left in the tank compared to the gas system. However, the recovery of the gas system, which has 1/3 more burner and 5/8 as much water to recover is far better. The recovery specs for each system show that the gas will recover at approximately twice the rate of the electric. The analysis doesn't include this, you can see the numbers in the specs from Rheem and others.

                    This answers my question regarding the ability of the electric to do a decent job at a tank temp setting of 120F. Despite the 80 gallons of storage and the associated operating costs, it’s not a great performer and isn’t really substantially different than the gas system.

                    I next changed the t-stat settings to 125 for the electric and 135 for the gas. Assuming 5F loss in the pipes (I'm hoping they're well insulated), this gives 120 and 130 at the tap for the electric and gas rigs, respectively.

                    The results are:

                    Temp of tub filled with water, neglecting cool-down losses:

                    Electric system: 102.4F Gas system: 101.1F DIFFERENCE: 1.3F

                    Temp of the water in the tank right after fill:

                    Electric system: 94.8F Gas system: 87.4F DIFFERENCE: 7.4F

                    The tub temps are clearly much closer to what the user would want to see. Despite your preference for higher temps, one should not go above 104F. Even if you are foolish enough to discount the recommendations of the health authorities, you as a contractor open yourself up for liability should anyone experience a medical or injury problem and blame the installer.

                    The bottom line remains, though, that the dual electric system is buying you less than 1.5F at the tub, and less than 7.5F at the tank. The recovery time advantage – two to one - of the gas WH’s larger heat source will make up the tank temp difference in a very short time.

                    As for condensation, your favorite topic, you can see that the gas tank doesn’t dip below 86 and the electric tank doesn’t dip below 92. I don’t see this as posing a threat of excess condensation despite your concerns. Not very common for the dew point to be above 85F.

                    The numerical accuracy of the solution, if you’re interested, is over 99.99%.

                    So here’s the real bottom line:

                    (1) The gas system isn’t as good of a performer as the electric system in terms of tub fill – no surprise there - but only by a very small margin. The small margin is a surprise.
                    (2) The gas system will have less hot water available right after tub fill, but will recover faster.
                    (3) You can’t set the t-stat at the tank at 120 with the electric rig and get an adequate tub fills. You will have to crank it up to get 120F at the spout. Similarly, you will need to set your gas WH to realize 130 at the spout.
                    (4) Not really going to see excess condensation with the gas WH UNLESS the water heaters area installed in areas where the dew point is above 85F…
                    (5) Every 5F decrease in main supply temp cuts the fill temp for the gas system 2F, and cuts the fill temp for the elect system 1.5F. Again, not a surprise that the larger capacity system would do better with colder supplies due to less dilution.
                    (6) A single 50 gal electric, the data for which I didn’t cite above, will result in a couple degrees lower tub fill temp. More importantly, the poor recovery performance will, IMO make that solution unsatisfactory.

                    BTW, if you have one of those 6 gpm tub fill valves, the additional draw rate will cost you quite a lot - several degrees of tub water temp. Don’t open it all the way. 4gpm (15 min to fill the tub) is a pretty good place to operate.

                    Finally, is your 60 gal tub capacity the operating capacity or the overflow capacity? A human, excluding head, will take up 12 gallons for a 120 pound person and maybe 18 for a 170 pound person. I didn’t account for this, figuring your 60 gallons was a typical operating fill spec. Obviously if the 60 gal is the overflow spec, this will make everything look much, much better.

                    So, Mr. Master Expert…. That’s the deal, and it’s not based on rules of thumb.


                    Comment


                    • #55
                      Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                      Originally posted by Andy_M View Post
                      I know that I said I was done with this thread. But you can’t let it drop, can you? So here is the last thing (really) that I’m going to offer on this topic. You might find it interesting, if you can get past your need to be the all-knowing expert.

                      First of all, you made a stink about me having to run my 40 gal heater above 120F. Duh. I said I was doing this all along. Moreover, I said, and believe, that OP would have to run the 50 gal gas WH above 120 as well. Read the posts.

                      It occurred to me that it’s doubtful if you could fill a 60 gal tub to a reasonable temperature even with your 40 gal electrics set at 120 *at the WH* as you claim. That’s to low of a temperature in general, leading to too-low temps at the faucets in the house. I think 120 is a good temp AT THE TAP. But it’s not a disaster to have it set a little higher. In fact, for older dishwashers without booster heaters you need the water temp – at the dishwasher - to be above 130 or even 140 to get good performance. Some recommend that the water heater temp should be at 130 or above for bacteria control reasons, although I’m not a biologist (you, being an expert and master, probably are… since you apparently know everything) and thus can’t say either way. But some do favor such high temps.

                      As I said long ago, I do have my little 40 gal turned up all the way, whatever that is, and it’s been doing fine out in the garage since 1995. So running the tank a little higher isn’t a guarantee of short lifetimes. Steel and glass tanks don’t really care about 120 versus 130 or 140, and the gas burner doesn’t even know that the water temp is.

                      In any case, and even though you are an expert and prefer to play with your “rule of thumb” numbers, I am not an expert and need to do a little real analysis to get a better idea of what is really happening with dual 40 gal electrics and 50 gal gas water heaters when it comes to filling a 60 gal tub. It’s not too time consuming, and since you don’t like my rates ($135, btw, not $145 -- but for you, I would only charge $155), I did it just for fun.

                      Here’s the parameters I used:

                      DUAL ELECTRIC WATER HEATERS (Master’s expert, never-been-wrong proposal)

                      Tank capacity = 2 x 40 gal = 80 gal
                      Burner = 2 x 4500W, simultaneous operation (30717 BTU)
                      Tub fill size = 60 gal (assume this is actual fill, not overflow capacity)
                      Main supply temp = 55F
                      Tank T-stat temp = 120
                      T-stat deadband = 7F
                      Temp loss in pipe from WH to tub fill valve = 5F (assume new install very good insulation)
                      Tub fill valve flow rate = 4 gpm
                      Energy factor = .92

                      GAS WATER HEATER (andy_m’s lowly, non-expert opinion)

                      Tank capacity = 50 gal
                      Burner = single 40,000 BTU/hour
                      Tub fill size = 60 gal (assume this is actual fill, not overflow capacity)
                      Main supply temp = 55F
                      Tank T-stat temp = 130
                      T-stat deadband = 7F
                      Temp loss in pipe from WH to tub fill valve = 5F (assume new install very good insulation)
                      Tub fill valve flow rate = 4 gpm
                      Energy factor = .62

                      Here are the results:

                      Temp of tub filled with water, neglecting cool-down losses:

                      Electric system: 98.8F Gas system: 98.1F DIFFERENCE: 0.7F

                      Temp of the water in the tank right after fill:

                      Electric system: 92.3F Gas system: 85.8F DIFFERENCE: 6.7F

                      In other words, there isn’t a hill of beans worth of difference at the tub. Neither is really hot, so I hope OP’s tub has an internal heater.

                      Not surprisingly, the electric system has more, hotter water left in the tank compared to the gas system. However, the recovery of the gas system, which has 1/3 more burner and 5/8 as much water to recover is far better. The recovery specs for each system show that the gas will recover at approximately twice the rate of the electric. The analysis doesn't include this, you can see the numbers in the specs from Rheem and others.

                      This answers my question regarding the ability of the electric to do a decent job at a tank temp setting of 120F. Despite the 80 gallons of storage and the associated operating costs, it’s not a great performer and isn’t really substantially different than the gas system.

                      I next changed the t-stat settings to 125 for the electric and 135 for the gas. Assuming 5F loss in the pipes (I'm hoping they're well insulated), this gives 120 and 130 at the tap for the electric and gas rigs, respectively.

                      The results are:

                      Temp of tub filled with water, neglecting cool-down losses:

                      Electric system: 102.4F Gas system: 101.1F DIFFERENCE: 1.3F

                      Temp of the water in the tank right after fill:

                      Electric system: 94.8F Gas system: 87.4F DIFFERENCE: 7.4F

                      The tub temps are clearly much closer to what the user would want to see. Despite your preference for higher temps, one should not go above 104F. Even if you are foolish enough to discount the recommendations of the health authorities, you as a contractor open yourself up for liability should anyone experience a medical or injury problem and blame the installer.

                      The bottom line remains, though, that the dual electric system is buying you less than 1.5F at the tub, and less than 7.5F at the tank. The recovery time advantage – two to one - of the gas WH’s larger heat source will make up the tank temp difference in a very short time.

                      As for condensation, your favorite topic, you can see that the gas tank doesn’t dip below 86 and the electric tank doesn’t dip below 92. I don’t see this as posing a threat of excess condensation despite your concerns. Not very common for the dew point to be above 85F.

                      The numerical accuracy of the solution, if you’re interested, is over 99.99%.

                      So here’s the real bottom line:

                      (1) The gas system isn’t as good of a performer as the electric system in terms of tub fill – no surprise there - but only by a very small margin. The small margin is a surprise.
                      (2) The gas system will have less hot water available right after tub fill, but will recover faster.
                      (3) You can’t set the t-stat at the tank at 120 with the electric rig and get an adequate tub fills. You will have to crank it up to get 120F at the spout. Similarly, you will need to set your gas WH to realize 130 at the spout.
                      (4) Not really going to see excess condensation with the gas WH UNLESS the water heaters area installed in areas where the dew point is above 85F…
                      (5) Every 5F decrease in main supply temp cuts the fill temp for the gas system 2F, and cuts the fill temp for the elect system 1.5F. Again, not a surprise that the larger capacity system would do better with colder supplies due to less dilution.
                      (6) A single 50 gal electric, the data for which I didn’t cite above, will result in a couple degrees lower tub fill temp. More importantly, the poor recovery performance will, IMO make that solution unsatisfactory.

                      BTW, if you have one of those 6 gpm tub fill valves, the additional draw rate will cost you quite a lot - several degrees of tub water temp. Don’t open it all the way. 4gpm (15 min to fill the tub) is a pretty good place to operate.

                      Finally, is your 60 gal tub capacity the operating capacity or the overflow capacity? A human, excluding head, will take up 12 gallons for a 120 pound person and maybe 18 for a 170 pound person. I didn’t account for this, figuring your 60 gallons was a typical operating fill spec. Obviously if the 60 gal is the overflow spec, this will make everything look much, much better.

                      So, Mr. Master Expert…. That’s the deal, and it’s not based on rules of thumb.

                      Thanks for proving to everyone and yourself that dual 40 gal electrics would be the better choice and the safer choice. I knew it before the slide rules were broke out.

                      For you not be going by rule of thumb you sure assume alot. Like the heat loss in the supply pipe,the displacement of the water in the tub by the person,fill rates of the tub,where the water heater will be installed,etc etc.

                      Your also assuming a constant incoming water temp. Rule of thumb is used for good reason as one variable may be present but offset by another variable that can cancel each other out but both conditions exist but will not be noticed until one of the two variables is changed or is acted upon by other factors like the type of valve used to fill the tub,the material of which the tub is constructed and most of all the habits of the owners or potential NEW owners. Thats why there are guidlines for water heater sizing....it keeps people from cranking up smaller tanks to satisfy larger demands leaving an un-safe operating condition...possibly for future owners.

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                      • #56
                        Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                        Let me also tell you why your numbers are wrong and i noticed it immediately but you probably do not understand how the two types really operate.....being you really dont do this for a living I kinda understand.

                        The problem is with the "deadband" as you call it. They both will never be the same and the gas will always have the smallest "deadband" as you call it.
                        A gas water heaters thermostat is submersed into the tank while an electric thermostat is simply pressed against the tank and relies a great deal on thermal transfer through the tank. The result is the electric will be slower to "fire" once a draw is made. This is compounded by the manufacturers shortening the lenght of the dip tubes to prevent thermal stacking. Notice on one of my very first posts I suggest piping the cold water to the drain opening in the electric tanks and feeding them from the bottom. I'm way ahead of ya ANDYM

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                        • #57
                          Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                          You're amazing.

                          No one ever said that dual electrics wouldn't perform be better. The discussion has been about whether it was needed and whether it was cost effective. What I learned was that they don't perform *significantly* better, and that running them at 120 at the tank as you, the Expert, said woldn't be acceptable.

                          I think it's pretty clear that what dual electrics get you *in this application* is twice the failure rate, twice the complexity, twice the sapce occupied, higher operating costs (although maybe not for you) and worse recovery. Oh, and a one degree higher fill on the tub. Obviously better, right Mr. Expert?

                          All the assumptions are the same for both. Which makes sense, it's the same installation, isn't it? You rules of thumb don't account for anything in terms of t-stat deadband, draw rate, burner size, etc. Yet in your narrow little way of looking at things, you're rules of thumb are better. Well ok, if you say so, You're the expert.

                          No knowledge ever entered anyone through an open mouth. Funny, I like this place because I learn a lot from these guys about plumbing and electrical. Once in a while, my background alows me to contribute. One would think that you would be open to learning something, but I guess your ego gets in the way. Perhaps you're a good plumber. I hope so.

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                          • #58
                            Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                            Originally posted by TheMaster View Post
                            Let me also tell you why your numbers are wrong and i noticed it immediately but you probably do not understand how the two types really operate.....being you really dont do this for a living I kinda understand.

                            The problem is with the "deadband" as you call it. They both will never be the same and the gas will always have the smallest "deadband" as you call it.
                            A gas water heaters thermostat is submersed into the tank while an electric thermostat is simply pressed against the tank and relies a great deal on thermal transfer through the tank. The result is the electric will be slower to "fire" once a draw is made. This is compounded by the manufacturers shortening the lenght of the dip tubes to prevent thermal stacking. Notice on one of my very first posts I suggest piping the cold water to the drain opening in the electric tanks and feeding them from the bottom. I'm way ahead of ya ANDYM
                            Actually I do undersand deadband. By using the same, I give you the advantage in the calculation. Guess you didn't get that this weakens your position, I was helping you.... but then again there's plenty you don't get. You must be too far out in front.

                            Off to the be with the family. Happy Easter all... even Master!

                            Comment


                            • #59
                              Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                              Originally posted by Andy_M View Post
                              Actually I do undersand deadband. By using the same, I give you the advantage in the calculation. Guess you didn't get that this weakens your position, I was helping you.... but then again there's plenty you don't get. You must be too far out in front.

                              Off to the be with the family. Happy Easter all... even Master!
                              No I dont think you understand or else you wouldn't have presented it in the way that you did. Call that help if you want....I call it not understanding what your trying to talk about and when its pointed out you claim your helping me. Ok right.

                              What you dont get is that by eliminating the dip tube I can get more hot water out of my tanks...thats why I advised to pipe them the way I did from the start.

                              Dont take it so personal.

                              By the way....if you were right you would have 50 people by now teaming up with you.....I dont expect anyone to help me because I'm proving what they already know from personal plumbing experience.....your looking in books and not considering any practical installation other than your own home......I work in and on thousands of homes and use a book for reference.

                              So Rheem has the condensation issue all wrong......they dont know do they? They are just "mr experts" too that cant keep their mouth shut and learn from a guy with a tub and a 40 gal cranked up.....Like You!!!!

                              Oh and for the record....the dual 40 gal electrics have a 2.5 gph better recovery rate than your 40,000 btu burner. Your not figuring each electric tank independently and then combing the recovery like you should be. The 50 gas would recover at 56.5 gph and each electric tank would recover at 29 gph each for a total of 59 gph. You still would have less water at the end of the recovery also.
                              Thats with both figured on a 65 degree rise and all tanks set to 120 degrees.

                              Why do you insist on saying you would have twice the failure rate??? Thats just not the case. The more stable the tanks temperture stays and the lower the tanks temp the longer the life of the tank all else equal. Dual water heaters can achieve this better than over taxing a smaller heater by increasing the temp.
                              Last edited by TheMaster; 04-24-2011, 06:07 PM.

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                              • #60
                                Re: Electric Hot Water Heater vs Natural Gas Hot Water Heater

                                Here the more electricity you buy the cheaper it gets. Same with gas. I hafta have electricity and we do not have much of a winter most years so heating the home is not much of an issue. I cnt use gas to cool my home so again electricity is a must. Gas is not.

                                Thats why an electric water heater is cheaper for me. By having a gas water heater I would pay the highest rate because I would not be buying very much per month and it would in turn cause my rates to increase on my power bill because I wouldn't be using quite enough power to throw me into a cheaper rate.

                                My dual electrics would have almost zero standby loss over a 24 hr period. Not so with a 50 gas standing pilot with a flue that cant be insulated. having to keep the 50 gas at a higher temp to deliver the demand will also cost you more and wrecks the energy guide comparison your trying to make.

                                Dual 40's would provide enough hot water and a great recovery rate and a more reliable hot water source than one 50 gal tank. lower temp=langer life for the electrics. Dual water heaters have a synergy effect making them work better than one tank of the same capacity.

                                ANDYM......if filling a bathtub with water over 104 degrees was a big liability for the contactor...then why does Rinnai allow a water temp of up to 120 degrees for their bath fill feature? I'll be waiting for your answer on that one.
                                Last edited by TheMaster; 04-24-2011, 07:26 PM.

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