On Demand Water Heater

T bone

HO wants an "in-line" water heater, meaning one of those "on demand" types. We're installing a special shower for him that has multiple shower heads rated to flow up to 20gpm, tho I don't think he'd ever run it that heavy unless there's something I don't know about plumbing. (There is a LOT I don't know!).
I can't locate an electric on demand water heater that looks like it could keep up. Anyone have experience with these?

I'm a small home improvement outfit with a 4 man crew and subcontract any plumbing. I want to be able to talk smart with the HO so am trying to learn more about this.

John S

How about a gas one...?

__________________
John
www.ready4rent.ca

Ishmael

Definitely have to go gas, but I don't even think there's a gas unit that can keep up with 20gpm demand. They're generally good for (I think) 10-12gpm, and an electric one maybe half that. PLUS, I remember researching the electric units once for a HO that asked about them, and found that they draw over 100 amps by themselves!

mdshunk

For that sort of GPM, you're gonna have to do two or more units in series (or maybe parallel, I forget). There are kits from the on demand water heater manufacturer's for this purpose to interconnect the brain of each unit so they all know what's going on. Common for restaraunt dish rooms.

troubleseeker

I don't think you can even get close o that flow with a top of the line gas unit, much less electric. You may be able to meet that with a commercial unit, but talk to the customer's heart doctor before telling him the price of any high output commercial heater.

Two top end units, piped in parallel may work ok, but once again, that is a pricey option. In series would not increase the flow capacity, but would allow you to maintain maximum flow at maximum temp rise, even with very cold supply water, because the first unit would be acting as a preheater for the second unit in the series.

Am I the only one who sees the absurdity of this.....somebody who wants a 20gpm shower system, and thinks he wants to have an on demand heater to conserve?

mdshunk

Right.... those zillion body spray showers are normally supplied with a storage tank/circulator/domestic coil in a furnace arrangement. BIG piping to the shower too. Last one I saw had 1-1/4" copper to the shower area.

Ishmael

It's just like the master shower I installed in this 7 bath "summer cottage" I recently roughed: Sunflower head in the ceiling, four perimeter showerheads, and a handshower all run off two mixers (Waterworks) and 6 stop valves. I ran 1 1/4" to the master bathroom, and made the shower drain and trap 3". What a nightmare.

JamesNLA

Ok here's the deal. I have an idea of the set up they have and have done them before.

First, Just because the shower is rated for 20 GPM does not mean it will pass 20 GPM of ONLY HOT WATER. Figure 80/20 (80% hot - 20% cold)

Next you need to size the unit correctly, and in my personal opinion you don't have near the experience to pull this off correctly, but maybe you will get lucky with a plumber who actually knows what he is doing.

I almost always sell and install Noritz Tankless Heaters. Hands down they are the best. Some will disagree, and that's fine. I have been installing these units for a while now, and I know what I am talking about. If you don't want Noritz go with a Takagi they license out alot of Noritz technology in their units.

As for plumbing in series or parallel, may I suggest you not mention those words to your client....ever. If you don't know what they mean and fully understand exactly how that works, you may smell of BS and loose the job.

And FYI, if you go mulitple units it would be done in parallel.
Noritz units actually trade off the larger demand every 24 hrs, so there is equal wear and tear on them, and a host of other really cool things when connected together with a data cable, but I worked my a$$ of today and am pretty tired to type it all out.

As for which unit(s) to go with, you need to understand this is not just a simple thing to do correctly. It can and will get very expensive - very fast.

Starting out with the unit. You could go with 1 13.4 GPM unit that unit runs somewhere around 2500.00 and takes up to 345K BTU's of gas supply (get back to that later). If this was my gig, I would probably go with 2 8.4 GPM units (in 2 months there is a new 9.1GPM comming out)

So with that I would get at MAX 16.8 GPM of hot. Price is 1500 each.
They EACH take up to 235K BTU's
Also, these would be dedicated heaters, meaning they wouldn't supply the rest of the house......it just depends how custom this client wants it. That decision is subject to change depending on a few factors, like budget and customer needs/wants and the property layout. Really, a qualified plumber could make that call.

Next, GAS GAS and more GAS. Plan on a new meter and a new gas line directly to the heaters. Again, a plumber can properly size and install that....it ain't cheap.

Location of the heater, they can go outside in the attic or almost anywhere. Again a licensed plumber SHOULD be up to speed on local codes as well as the UPC, also following the manu's instructions for installation is very important......if only more people actually took the time to read things.....

There is one thing you may want to know about and that is about the graph for temp rise. If the heater has to do 40 degrees of heating that takes X amount of energy to do....there will be a GPM output from the heater with that temp rise. Average temp is 60 degrees temp comming in is 60 temp going out is 120...60 degree rise, so a 8.4 (RATED) GPM heater will NOT give you 8.4 gallons with a 60 degree temp rise. Make sense? This is important to know about because after your client has paid you something around 20 grand for all this you want it to work better than he expects. May I suggest you start reading your a$$ off if you care to know what you are talking about.

It's very easy to screw somthing like this up and experience far outweighs corporate graphs and ratings, however when done correctly it truley is something very cool to see working.

good luck

EDIT: Here is what they can/should look like in parallel, mind you this picture was taken about 90% complete, in an apartment building I did, it was pretty ghetto out there....

MSSI

I agree Noritz is the best.. highest priced, but best performance. A must for mid to large applications.

T bone

Thanks--ya'll are great & I learned enough to know I don't want to try this on my own. And much thanks JamesNLA. I think I can talk sense with the HO now--I know he doesn't want to spend that kind of money on hot water.

rservices

Speaking about in line heaters.

Is it possible to install a moble unit for powerwashing that run's on 110 volt.
It would have to be on the exit side of a powerwasher (pumps cant handle the heat)
Possibly 5 to 8 gpm

MSSI

not the ones we are talking about

rservices

Anything like that out there, To buy a hot water unit is anywhere from $2500 to $3000, I dont need one often, and to but one would take along time to make any money on.