Hot Water System

[Birddoggiest]

Im am doing a house with 4 showers, all with two heads a piece and one of them with seven heads plus a 72 x42 tub ect.... I need to size the hot water system to meet demand. I don't know if two 75 gal is enough. I thought about a hybrid system with a tankless inline but have never done it before. Rinnai reccommends 3 heaters and a 80 gal storage tank. Seems over kill especailly for a spec house, any ideas?

[PLUMBER RICK]

just guessing i would think that 2- 75 gal. heaters piped parallel with circ loop would be plenty.

if you really want to overkill, a 100 gal. 199,000 btu heater will do more than they can handle.

3 tankless and a 80 gal. tank is nuts. that's roughly 600,000 btu's and $4000. in equipment, not to mention piping cost.

rick.

remember this is a house, not a hotel.

[NHMaster3015]

Why not run the numbers? You should be able to get a pretty accurate sfu count and then size to the demand.

[FINER9998]

"sfu count"? what does this stand for?

[wrench spinner]

Supply Fiture Units as opposed to DFU's or Drainage Fixture units

[FINER9998]

and in a full bath with a toilet, bathrub and sink, would the sfu be 3 and the dfu also be 3?

[wrench spinner]

and in a full bath with a toilet, bathrub and sink, would the sfu be 3 and the dfu also be 3?

No.
SFU's
Water Closet with Flush Tank 2.5, Lavatory 1.0 and Shower, 2 SFU per head. Total SFU's would be 5.5 SFU.

DFU's
Water Closet 3 DFU, Lav. 1 DFU, and Shower 2 DFU Totaling 6 DFU's

I believe that these number are pretty much standard everywhere I got them out of the NYS Plumbing Code

[ridgidpipe]

If Its a Spec House you are doing I would think 2 75 gal would be sufficient but if it is for a builder I would just see how much he wants to spend first.

[JCsPlumbing]

Im am doing a house with 4 showers, all with two heads a piece and one of them with seven heads plus a 72 x42 tub ect.... I need to size the hot water system to meet demand. I don't know if two 75 gal is enough. I thought about a hybrid system with a tankless inline but have never done it before. Rinnai reccommends 3 heaters and a 80 gal storage tank. Seems over kill especailly for a spec house, any ideas?

Been here. Just a tip you probably though of but... watch your water volume & pressure calculations. If private, you have figure the pump correctly. If on municipal, sometimes you even have to request a larger meter.

J.C.

[NHMaster3015]

If you are calculating sfu's for hot water, you can eliminate the w\c and all the other colds.

[Birddoggiest]

just guessing i would think that 2- 75 gal. heaters piped parallel with circ loop would be plenty.

if you really want to overkill, a 100 gal. 199,000 btu heater will do more than they can handle.

3 tankless and a 80 gal. tank is nuts. that's roughly 600,000 btu's and $4000. in equipment, not to mention piping cost.

rick.

remember this is a house, not a hotel.

I talked to AO Smith rep and they reccommend the new 96% Vertex heater, 50 gal and 65 degree rise at 4 gpm. She also reccommended leaving provisions to add another if it doesn't meet demand.

[PLUMBER RICK]

I talked to AO Smith rep and they reccommend the new 96% Vertex heater, 50 gal and 65 degree rise at 4 gpm. She also reccommended leaving provisions to add another if it doesn't meet demand.

that will never fly. basically it's a hybrid type heater. high btu's and tank. 4 gpm is as low as some of the tankless units.

problem with most tankless is the gpm. not the gph. you need to figure the gpm demand. remember this is a spec. house. you don't know what type of family is going to buy the house. is it just 2 people or is 10 trying to all get ready and showered at the same time. it should be sized for all showers at the same time. but remember that showers are suppose to be 2.5gpm. removing the flow restrictors will turn those into 7-10gpm.

years ago a hotel next to universal studios, asked one of our plumbers to replace all the shower heads in a 200 unit building. they supplied the heads and requested them him to remove the restrictors. guess what. not enough hot water when the hotel was busy. he had to go back and reinstall all the restrictors.

rick.

[Birddoggiest]

that will never fly. basically it's a hybrid type heater. high btu's and tank. 4 gpm is as low as some of the tankless units.

problem with most tankless is the gpm. not the gph. you need to figure the gpm demand. remember this is a spec. house. you don't know what type of family is going to buy the house. is it just 2 people or is 10 trying to all get ready and showered at the same time. it should be sized for all showers at the same time. but remember that showers are suppose to be 2.5gpm. removing the flow restrictors will turn those into 7-10gpm.

years ago a hotel next to universal studios, asked one of our plumbers to replace all the shower heads in a 200 unit building. they supplied the heads and requested them him to remove the restrictors. guess what. not enough hot water when the hotel was busy. he had to go back and reinstall all the restrictors.

rick.

What is the general cost of a 100gal 200k btu? The Vertex is about 1900.00

[Plumbus]

"If you are calculating sfu's for hot water, you can eliminate the w\c and all the other colds."
But, don't forget the dishwasher. And it's wsfu (water supply fixture unit).
What kind of heating is proposed for the house? A combi system w/a condensing boiler and an indirect tank is a sweet setup. Because it supplies both heating and hot water, the high cost of the system can be more easily justified.