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  • Radiant/Domestic Heating

    Hey guys,

    New to posting in the forum but have been reading quite a bit. I know that this question has been asked before and everyone has different answers but would like some guidance for my particular situation.

    I have in slab heat piped in my basement and currently just have a 32,000BTU 40 Gal heater for domestic. I am looking to replace the current water heater and get my slab heat up and running. I have had two plumbers come out to price an install for an upgrade to my water heating situation. One guy wants to install a 75,000BTU 50GAL State water heater for both domestic and floor heat. The floor heat would just circulate through the water heater and domestic would also draw off of this. I do not like the idea of fall start-up when the slab is cool, or every start-up for that matter, getting luke warm water at the taps!

    The second guy would like to install a water heater, direct vent, and an 80,000BTU cast iron boiler for the floor. I like the idea of having the two separate and having the reserve for domestic.

    I was originally wanting to have a instant water heater for both, but I know with the cold inlet water (canada) and sometimes minor silt coming from the well, that a heater like this can be troublesome.

    I think a 40,000BTU 40GAL water heater is plenty for domestic (we have limited flow from well anyways) but what would be a good boiler/heater for the floor. Or do you guys have any other ideas that would outperform both scenarios.

    Thanks in advance as I appreciate ANY questions or comments!

  • #2
    Re: Radiant/Domestic Heating

    You can't be this for the affordability and versatility.
    This is expandable for solar or wood stove exchangers,too.


    • #3
      Re: Radiant/Domestic Heating

      So the slab does not currently have a heat source? How do you heat the rest of the house? Probably need more info to help you out.

      Did one plumber quote you for something like this?
      Water heater with built in heat exchanger

      Another option is this:
      A boiler with a built in tankless heater


      • #4
        Re: Radiant/Domestic Heating

        Thanks for the reply's.

        This is the exact model that the first guy is recommending.

        Which is similar to the product you mentioned p-crack but it doesn't have an exchanger, which most likely reduces cost. I am worried that having an internal exchanger is not a good idea, possibly issues in the future, and should use an external bronze plate???

        Currently we have a furnace upstairs providing heat. The basement is very cold during the winter but above freezing with furnace heat. The idea is that the basement slab will provide primary heat for the house and the furnace will make up any necessary heat for cold weather


        • #5
          Re: Radiant/Domestic Heating

          Also p-crack with the bradford white type of internal exchanger I am worried about exchanger loop BTU output.

          If you look at the last page of this manual it says the BTU ratings for the exchanger loop, but at 180 degree tank temperature!!!!!!! Can you say burnt baby

          Wonder what it would really put out at 100-110 tank temp.

          What are your thoughts on this???


          • #6
            Re: Radiant/Domestic Heating

            the water comes out of the heater at or near 180 degrees and immediately meets a tempering valve to reduce it to your desired potable water temp, it really is a great system.
            No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.


            • #7
              Re: Radiant/Domestic Heating

              So with that being said what is the best value on the market in your opinion, can you get a water heater with exchanger for $1500 that will last a long time?? Also, just thinking that it might be worth the extra money for a modulating unit. Doesn't make complete sense to me for a 75BTU unit to have a 40BTU heat exchanger when it cannot modulate down, it would be cycling continuously when the floor is being heated, wouldn't it???

              Last edited by bradal; 10-18-2009, 11:52 AM. Reason: More Info


              • #8
                Re: Radiant/Domestic Heating

                There is no shortage of products on the market for what you want to do. You just need to find the right one that fits your needs.

                The Combi2 like MoJourneyman said has a tempering valve so no worries with scalding. I would lean towards that as the best option unless you need more than 38,000 btus for your primary heat source.

                The State heater the plumber quoted is a very nice high efficiency heater and if you were in the US would qualify you for a substantial Federal Tax Credit to offset the cost of installation. I would NOT use it for space heating only because it doesn't have a separate space heating heat exchanger. Issues with disposal of condensation and venting restrictions are another drawback.

                And no, you won't get a water heater with heat exchanger that modulates for $1,500. Dream on......
                Last edited by plumberscrack; 10-18-2009, 11:59 AM.


                • #9
                  Re: Radiant/Domestic Heating

                  Just so I can get an idea of price difference, would these prices be about right for average unit in each class, or even the ratios

                  Mid/High Efficiency Water Heater 75,000BTU 50GAL -$1000
                  Same water heater with exchanger-$1750
                  Modulating 30-100BTU water heater with Exchanger-$3000

                  Also same topic different equipment :P I am looking for a t-stat with some sort of outdoor reset to use with my slab. I know Tekmar has a few offerings but ones with outdoor reset have alot of unnecessary controls for this sort of set-up (one circ pump, no boiler).

                  Any suggestions. Sorry for all of the questions just looking to have a good discussion with the plumber on Monday.

                  Last edited by bradal; 10-18-2009, 01:15 PM.


                  • #10
                    Re: Radiant/Domestic Heating

                    Others may disagree but forget about using an outdoor reset control with radiant heat. The lag times are too great to make it efficient. Get your slab up to temp and keep it there using a standard thermostat. Keep it simple, just use a Honeywell 832A circulator relay and a 24 volt thermostat.


                    • #11
                      Re: Radiant/Domestic Heating

                      I appreciate the reply Plumberscrack. So do you recommend maintaining a temp in the slab with a reg. thermostat or trying to maintain a room temp, or a combination of the two?? I was thinking that with a heat exchanger in the hot water tank you could have a variable 4-way mixing valve that modulates to maintain a slab temp of say 75 with the recirc pump in the secondary piping. Does this make sense or would that be complicating things?


                      • #12
                        Re: Radiant/Domestic Heating

                        Originally posted by plumberscrack View Post
                        Others may disagree but forget about using an outdoor reset control with radiant heat. The lag times are too great to make it efficient. Get your slab up to temp and keep it there using a standard thermostat. Keep it simple, just use a Honeywell 832A circulator relay and a 24 volt thermostat.

                        Why not a TACO SR501???? And a Simple comfort 1800????