There isn't near enough information.

What are the lowest cold water temps in the winter?
How much hot water do you reasonably expect to use at the same time - in gallons per minute?
What model (not just brand) of water heater is proposed.

That's what we need to know to answer the question.

Now- I know that you aren't asking me this, but I will say it anyway. This type of shower setup is extremely wasteful. When we are facing water shortages and sucking up a third of the world's energy - much of it imported from countries that don't like us very much -- I see this sort of nonsense as unpatriotic and gluttonous.

The sooner we start taxing carbon, the faster this sort of nonsense will stop. Why don't you just flush $20's down the toilet? It would be less offensive because it would only be hurting you.

Thanks Jake (and yeah, I wasn't asking ;) )

I don't know the model of Rianni yet. I will get it. As I understand it, the DTV II can pull 22 GPM if everything is turned on. I don't see happening all the time, however. The AMMA is a 65 gallon tub.

We live in Pittsburgh so winters can get pretty cold -- I don't know what that translates to for water temps.

You really need to do a reality check:

A standard shower is 2.5 gpm. This is about 10x that.

A 200k btu/h tankles (the largest unit most make- although Rianni does make a 237k unit) will produce ~5gpm at a 65 degree temp rise (from 40 to 105). Even two of these- pulling an incredible 400k btu hour wouldn't provide half of your load.

Looked at another way, it would empty an 80 gal water heater set at 140 degrees in less than five minutes.

Good luck with that.

So by that math I guess I need 4 Riannis in serial and probably another one for the rest of the house, eh? I suppose I can do that but it sounds cumbersome.

Anyone actually have a DTV II? While it says that it has a max 22 GPM, what do each of the heads produce?

Also, anyone know anything about Drainwater Heat Exchangers? -- could that possibly help?

Keep in mind the gas supply to the house. It will have to be up-sized to supply five heaters + any other uses.

For this use, drainwater heat exchangers will help a LOT. They get a good bit of pre-heat out of the drain water, especially in the winter with barely-above-freezing input water, and reducing that differential will dramatically decrease the load on the water heaters. 30 degrees of rise in inlet temperature in winter is a frequently quoted amount - at that point you would easily be able to step down to twinned units.

Also, how many heads do you plan to USE at the same time? Has the drain been sized appropriately? You're probably aware of this but these systems require more than a standard 2" shower drain.

If you get 30 degrees rise out of a recovery unit, you would still not meet 22 gpm with two units. Two units would produce 19 gpm max - and you would have to hit all of the other numbers because that's where the output starts falling off (35 degree rise).

A recovery unit is better than additional heaters, this is still ridiculous beyond belief.

Geez, Jake, give me a break.

We're not going to be taking 22 GPM showers everyday. Occasionally we will put it in the mode where it *may* use quite a bit of water, but generally we're just taking a single head shower. I am simply trying to figure out what it'll take to ensure that it can pump out all of the heads if I decided to "floor" it.

I also drive a car that can go 180 MPH, but I rarely do 140.

Are you REALLY living such a clean, unwasteful life that you continue to give me crap about occasionally taking an over-the-top hot shower?

Hey bud,

I'm not going to get into a "who's greener" pissing contest. However, I will tell you that my monthly gas bill for a home in central Indiana - with all gas appliances - is $33 a month - without any exceptional sacrifices.

This is a plumbing forum. Too many people are thinking it's cool to install a multi-head shower or a 80 gal tub and they have no clue what that really requires in terms of energy, water, water heaters and drains to make that happen. Evidently your builder is one of those people; he planned on running this setup on one tankless.

Just having the capacity to do it, even if you don't use it often, requires commercial sized water and gas supply, water heaters, etc.

We are going through a period where a lot of people have lost their homes, in part because nobody was willing to make value judgments. Nobody was willing to say that what was going on was completely unreasonable. It became "normal" for people to buy more house than they could afford and carry stupid amounts of consumer debt.

I am not one of those people. I'm not going to pretend that what you are doing is okay. What you are doing is completely unreasonable. It's wasteful, it's ugly, it's distasteful, it's gluttonous. The fact that you can afford it doesn't make any of the previous statements untrue. The fact that you drive a car that can go 180 mph doesn't impress me one bit - it just confirms a pattern of ugliness.

To be clear, you have your values, I have mine. But I contribute to this forum for free - and I reserve the right to make value judgments when needed. If you don't like that, you can take some of that money that you are throwing around and hire a competent builder to design your plumbing system - the one that you have doesn't have a clue.

You really should be consulting a commercial plumber. This is well beyond residential plumbing. You will have to upsize every single thing feeding your home from the gas piping to additional pressure tanks on up. This isn't a job for a novice. And almost undoable with residential water pressure and gas supplies. SOmeone who builds hotels or spas might have ideas to be able to accomplish this, but it will be extremely expensive. Extremely expensive. If you have to completely resize all of your utilities from the street to the home, plus engage commercial equipment to heat and supply your shower, you may be in the 100K shower territory.

Thanks all for your feedback. My original question was if it sufficient and it appears that it is not. I am bringing in another commercial plumber to check the first design.

And Jake, I don't know where to start. Your last rant was all over the place.

You are completely right -- this is a PLUMBING forum. I didn't expect to get crap for asking a question about plumbing.

I suppose we could all live in 400 sqft houses with only the bare necessities but I am not that noble. I have a big TV, a big kitchen, a fast car (and am looking for a big shower). That said, I certainly am not living above my means. I have ZERO debt and I did it by working very hard for a very long time. And while I feel for those who have lost their houses and such, I'm not sure how I am connected to the economy failing. I'm not a fat-cat banker.

Perhaps you just don't like folks that have more than you have. ...or perhaps you are just very noble and better than I am. I don't know.

Hmm. Looking closer at the specs for the DTV valve box, it says the box can flow up to 22 GPM. Actual GPM will be determined then by the heads you put on the system.. look up the rated flow on all the heads, add it up, and see what that is. You may well find that it's much lower.

mr_nim.

I'll try this one more time and then give it up.

No, I really am not jealous of people who have more than me. I personally find conspicuous consumption ugly and offensive. I like fine things too - but being overtly wasteful because you can afford to isn't attractive.

But the problem here is that this sort of waste becomes "normal". "Everybody is doing it" becomes the rational. That's the connection to the home and debt issue in the earlier post. Many people, just like you, don't understand what is really involved or the degree of waste in a shower with half a dozen heads, each moving 2gpm or better.

We are really are facing serious challenges with the supply of both water and energy. Unfortunately, there will always be people who take the attitude "I've got mine, I can afford it, screw everyone else". It seems we've lost any sense of shared sacrifice for common good that we saw with the WWII generation.

I do think part of the answer is to tax energy much more than we do. It's the only way that I see to get people to act in a way that is more rational and reduce some of the egregious waste... like 22gpm showers.

Wow, JTWD, even if Mr. Nim can't be dissuaded, you've impressed me, so thx for your info and constructive arguments. In addition to the practical point of view tho, I have to add that I've lived long enough to witness many times over, and have, therefore, come to strongly believe in -- karma. Whatever we can get away with when not doing the right thing, either bc we have money or power, or bc no one is looking, will bite us in the a@@ at some point in some way -- no doubt.