How to size water heater(s) in new home.

[NoSpam99989]

I will be building a 100' long home with water usage at the two ends of the house.

At one end will be a mostly over the garage apartment for my daughter with kitchen, bath, laundry. Also there will be a bath with on the first floor with our kitchen and also laundry and utility tubs in the laundry and garage.

In the middle will be a 2nd floor guest bath.

On the other end will be a first floor master bath with shower and 72" jetted tub (Venus II).

A priority is not to have to wait "forever" for hot water to reach a spigot, especially at the kitchen & lavatory sinks and utility tubs.

I am planning to have a hot water heater in the garage and another under the master bath (crawl space here will be about 6 feet high due to land slope).

How large should I make each water heater. Should I have a separate additional heater for that huge tub and only turn it on when needed?

Many thanks for any knowledgeable help!

[Charles Spitzer]

some sort of return loop would be easier, and cheaper to run than 2 heaters.

regards, charlie

[PipeDown]

A recirculating loop with large primary tank is certainly a good way to do it (lower up front cost) but if the hot pipes are not very well insulated, the recirculating line will cause a lot of heat loss and wasted energy (higher long term cost). An on demand recirculating pump activated when you push a button as opposed to a pump on a timer or thermostat is more energy efficient in my opinion (though not as transparent or instant)

Two tanks is acceptable, I would consider plumbing the second tank in series with the first if located like you say as opposed to two parallel hot systems aside one cold. The series tank will allow quick delivery of hot water to distant fixtures and once the hot water from the primary tank started filling the second one, it would not need to heat as much water making the system more efficient. You would also effectively have the full volume of both tanks available to fill a big tub. Hot water branches can extend from the output of either tank. This configuration may also buffer the tub/shower supply from other uses like laundry (connected between the tanks)

A single on demand heater positioned more centrally in the house or two smaller units plumbed in parallel are also options.

My Guess: A 50gal primary tank and a 30 gal secondary sound like it might suit your needs. Of course you can go larger but it will effect your energy bill. The secondary tank only needs to be somewhat larger than the volume of water in the hot pipe between the two tanks (which isn't much) to work (prevent any cold water surges at the far end of the house) plus any additional volume of water you think the attached fixtures need before the tanks have time to reheat.

There are pros and cons to each configuration. Choose based on price and performance you feel comfortable with

[Joseph Meehan]

I would also go with the single HW heater and a return loop. Get the pipes well insulated or an on demand system.

As for sizing the HW heaters, maybe some more information would be in order.

How many people how many bath rooms. Dish washer?

How about schedules. Will everyone be using the hot water at the same time as also running the clothes and dish washers? Any big spas?

[Doug Boulter]

[e-mail] wrote on 09 Feb 2006:

You've left out some of the most critical data.

1) Gas or electric heaters? Gas will recover much more rapidly and can often be sized smaller. 2) How many in the family, and who are they? Small family, smaller size. Large family with teenage boys, bigger is better.

[m Ransley]

Running a circulator no matter how well insulated the piping will waist alot of energy. Look into 2 Ng tankless Takagi or Rinnai. Water heaters tanks only have a Energy Factor in the 60s, tankless go into the 90s.

[Michael Keefe]

If you're going to heat water with electricity, I would consider an on-demand type tankless heater. I think they cost around $500 and you'd be saving some labor on running a lot of extra line and insulation.

[NoSpam99989]

Someone rightly pointed out that I had left our critical info. Occupants: Wife & myself Daughter (in apt.) Water Heaters Either Elec or Propane Elec is much cheaper purchase & Install Propane expensive too Propane = Quicker recovery, possible tankless Apartment (upstairs): Bath: Tub/shower combo, lavatory, toilet Kitchen: Sink, D/W Laundry: Washer/Dryer Kitchen - pasrtly under apt Sink, D/W Small range side Sink Laundry: Util sink Washer/dryer Garage: Util sink ==== All above at one end of 100' long house ====== Guest bath (upstairs in middle) Lavatory, tub/shower combo, use mostly by guests Master Bed (at far end from the other stuff) 2 Lavatories 72" Jetted Tub Seperate shower A priority is not to have to wait "forever" for hot water to reach a spigot, especially at the kitchen & lavatory sinks and utility tubs.

I am planning to have a hot water heater in the garage and another under the master bath (crawl space here will be about 6 feet high due to land slope).

Options: 2 elec water heaters - one at each end - How big should they be? 3 elec water heaters - Separate one for jetted tub - on when needed 2 Tankless propane heaters Recirculating - rejected 200+ feet of pipe to loose heat from. plus cost to run pump, etc. Others?

How large should I make each water heater. Should I have a separate additional heater for that huge tub and only turn it on when needed?

Many thanks for any knowledgeable help!

[buffalobill]

who/what/where/when/why/how: good except your where = climate = recovery rate. there are other options for using hvac systems waste heat and an architect gives you a better answer. but from cold water 33 degrees in buffalo ny to 150 degrees of hot water is faster than yours will be on our big 75 gallon natural gas tank. you'd get two big electric tanks with as many timers as you can to run the two tank elements in each. and the circulators. electric hot water has slow recovery, so now that we see you have cheap electric available you get the largest residential tanks and you don't run out. you can run the electric recirculator pump on a start time of day like 15 to 30 minutes before morning shower time. adjust the tank temperature high enough so you can run as many of the devices as possible. see:

at: cooling calculator at:

[IBM5081]

My house is 90 feet wide. Two full baths on a 40 gallon on the west side of the house. Master bath, laundry equipment and kitchen on a 50 gallon on the east side of the house. Both natural gas fueled. The only time we ran out of hot water was on the west side when older son stayed in the shower forever. When it turned cold, he got out. Has not repeated since he left home. The dishwasher and kitchen sink are farthest from the water heater and take some time to get hot water coming out.