Remove 2 of the heads. And, creepy.

You put 4 shower heads in one shower so 4 people are showering in the same shower at the same time? How about you have different shower times? Your little kids will not be little kids for long and will not want to shower with mom and dad.

Can someone comment on the difference between one large tank versus two smaller tanks piped together in either series or parallel?

GPM per head x 4 x 15 minutes = gallons required.

If its 1.5 gpm heads x 4 x 15 then you need 90 gallons of mixed hot water. At 2.5 gpm you'll need 150 gallons of mixed hot water.

You could add a storage tank with a recirc loop.

hmmm, let me see... you removed the flow restrictors and put in 4 heads and now you don't have enough hot water.

Nope, not going to help you with that.

You are in the realm of a light commercial boiler. Not home production. You’d need 2-3 tankless in a cold climate. Larger systems like this require designing the support infrastructure from the municipality through the sewer with the output in mind. That includes the water main, to the water heating, to the drain sizes. As in, you require multiple 3” drains, even were you to manage the supply.

The Cook's Kitchen ,

You are not wrong - but one tankless can be borderline for residential gas supply -- 2-3 would definitely require upgraded gas service also.

Without the flow restrictors, nobody here knows what the flow rate is and so we can't calculate the needed water heating capacity if we wanted to. That's why Jeffrey R. Grenz, General Contractor's calculations are wrong.

The end user has to measure actual flow rates - and I'm not at all inclined to help him out.

I'm disappointed that a technical plumbing question has turned into value judgments from posters trying to out-snark each other rather than answers or suggestions for the problem I posted. If I wanted people to give opinions as to my decisions or lifestyle, I would have put this on Twitter. I was expecting a little more professionalism on this site.

The internet does not suffer fools kindly

Ben B,

So, let's be clear: To begin with "professionalism" kinda infers we are being compensated - we are not. We give our advice freely and we get to decide to whom and under what circumstances we give that. I have no problem calling people out for multiple shower heads and/or removing flow restrictors. You repeated the term I've used before to describe multiple shower heads -gluttonous - so I suspect you know where I come down on this already. If you don't like that - go pay someone to put up with your nonsense.

Second: You have actually been given very good advice. Not the advice that you want to hear - but good, solid advice that any "professional" would also tell you. I don't know in what part of the country you live, but the flow rates are code and we are not in the business of assisting people to circumvent that. Not only because of code/energy/water consumption issues but also because of what Cooks Kitchen said - This isn't an incremental change, this is a different class. It needs to be planned and not an after-thought. It would actually be unprofessional for us to help you along this path. I really question the professionalism of the plumber who participated in this remodel in the first place.

Third: As I pointed out, you have made it impossible for any of us to provide a technical solution even if we wanted to. We no longer know the flow rate of the shower heads. Without that information it would be unprofessional of us to offer guesses and conjecture - which is all we could do.

Jeff, I appreciate your attempt to help. I hadn't anticipated people on this site being as mean-spirited as they appear to be. I guess some of these guys think they're the plumbing police keeping the internet safe from fools like me!

They're doing our pan test right now so I can't get in there to measure the flow of the heads until the inspector comes, but if anyone is interested in helping with my original question, I'll try to measure tomorrow and see how much they're putting out.

There was a person on here a few months back with something similar to this. They had two 80-gallon tank, one with storage only and the other a commercial (200kbtu) unit. Also recirculation between the tanks.

Oh, and don't tell the inspector you pulled the restrictors out of the shower heads.

Thanks, Weedmeister. I won't mention it to him.

I've called 4 plumbers and gotten 4 different opinions. One wants to install 2 tankless heaters, one wants to do just one tankless, one guy thinks a brand new 75 gallon tank will be fine, the last one wants to do 2 50 gallon tanks. My head is spinning over here!

None will be enough supply. Not for 4 simultaneous restricterless heads. $$$$$ for what you want. Plus the fines. Plus the lawyer for the CPS charges.

Ben B.

I will give you a clue: If the inlet water temps are below 60 degrees, almost certainly all 4 of your plumbers are wrong - and most of them are very wrong.

Start with 2 of either and prepare to expand. Legal sized shower heads would be a better way to go and you could be looking at a red tag.

Had one client take restrictors out, preheating the shower while shaving emptied his water heater daily. I didn't offer to change it as the city (Davis) has a resale inspection.

The results of the tests are in. When all of them run, they pull 9 gpm in total. They don't fine in my city, but either way, it's under the 2.5 gpm per head limit. That's why it was pretty paltry flow with the restrictors in.

Can anyone who's generous with their knowledge help me with some math? Let's say we want to have a 15-min shower party where we all sit around and eat wet caviar and drink watered down champagne. 9 gpm x 15 = 135 gallons, but we're mixing our hot water with incoming cold water. Living in the Midwest, our ground water comes in cold in the winter, but cool in the summer. Assuming we accept we can't have shower parties in the dead of winter, how much do we need in the tank(s) to put out 135 of comfortably hot shower water in 15 minutes?

Thanks in advance for anyone who can solve my story problem!

The usual math (simple terms) is that you have the tank to cover immediate usage (say, within an hour), plus whatever new hot water is heated up within that hour. To do the estimate for how much you'd have for an hour you'd need to know the output of the gas part.

But in your case you effectively want the whole 135 gallons at once, minus whatever proportion of cold water is used in mixing (which will depend somewhat on time of year).

Simple answer: a storage tank of 50 gallons added to your 75 existing would probably be just enough for your extreme case (assuming not much losses, some cold water mixing, and you don't want to wash all your dishes immediately after). 75 gallon storage would give you a bit of extra margin (but not that much more). You can find calcs for how much additional hot water the gas will produce in an hour and decide whether that works.

Depends whether you want to occasionally run out or have a bit more buffer.

No moral judgment and no opinion on your code issues or whether tankless better.

Armoured, thank you very much. Nobody else had suggested keeping our existing tank and adding one to it. In what order should we pipe the two tanks?

If you're adding just a storage tank (with no heat of its own), it has to go after the one with the heat source. Speak to your plumber though - perhaps would make sense to install a simple electric (to avoid extra gas appliance and venting etc), if most of heating is being done by the gas one you have, electric heat would just be to keep water hot after being heated in other. You should also try to make sure both are well-insulated.

This may not be most efficient (equipment or operating cost), but it's possible and relatively simple. Look up the heat/recovery info for your existing hot water appliance (rough guide formulas out there on internet), i.e how much water will be heated by (##) BTU size.

Note, you haven't given any info on your existing set-up, I'm assuming a gas-fired water heater.

armoured,

The current one was installed by the prior homeowner in 2003, 55,000 BTU, natural gas, 75 gallon, it vents about 6 feet away out of the wall of the basement into a chimney. There are two other vent holes that were sealed from the furnaces when they were replaced in the early 2000s. Perhaps I could add a 50,000 BTU 50 gallon heater next to this one in series to add capacity now and then replace the 75 when it dies in a year or few?

Honestly, get some pros in to suggest solutions and look at your current tank. Lots of variables, including your specific needs. I think you've now got the basics - to cover your (somewhat unusual) demands, you need either a fair amount of storage (one very large or two large-ish tanks), a high output heater (possibly tankless), or some combination thereof. Then there's local utility rates and physical connections and up-front vs operating costs.

(And I'd include in considerations whether this is worth it to have four people showering at the same time)

Fair enough. Thanks!

I would be thinking in terms of an additional storage tank, non-fired or heated, in line with your current tank. Probably around 80 gallons. And a recirculation pump between them.

Going the tankless route, you'll need to know what your cold water temperature is. Units are rated at their temperature rise at a specific flow rate. 9gpm seems high to me for residential, but I don't really know. But if you have say 50* water coming in, you'll need to raise it 60* at 9gpm in order to run your shower. That seems fairly large to me.

BTW: The old thread I was talking about, the person had purchased a home that had something like two 120 gallon tanks, the first was storage only, the second was a commercial 200kbtu tank. The gas tank needed to be replaced and the plumber had quoted several thousand dollars to replace it. She opted to get a smaller residential tank and keep the storage tank in place, the difference being that the recovery time would be longer which was ok for her.

I mostly agree with weedmeister, I think the logical solution is most likely a storage tank/additional heating tank, and I didn't mean to be dismissive of the question.

There are always trade-offs, and the main one here is that the question/problem boils down to: what are the best options to provide commercial-level hot water service for 10-15 minutes a day?

After that, so many questions: what reliability? Is slightly worse (8 minutes?) okay during winter months? Same time every day, or randomly? Will needs change in a year? Budget constraints? Operating costs? Or is it 10-15 minutes at a time, 2, 3, 4, 5, 6 times a day? Etc.

In the classic "if it were me", I'd tell everyone to not shower at the same time, last person gets cold water (and I wouldn't be very popular, but then, I get up earlier than most in my household).

To meet the most simple parameters, I'd probably add a storage tank or additional hot water heater, perhaps put a timer on one or both of them to make sure hot water for all from 7-9 am (reducing costs the rest of the time). If location is relatively warm / high cost, I'd consider a heat pump water heater for the main (assuming gas/electric relative pricing works). If gas is cheap, perhaps run the existing gas boiler until it dies and consider options in future.

For anyone still interested...PROBLEM SOLVED. We consulted with a local plumbing supply house, who called their AO Smith rep. The solution was 2 75 gallon tanks piped in parallel. Four people can now shower at the same time and not run out of water. $3,000 was the total cost of tanks and installation.