I am in the middle of a bathroom remodeling job and have run into an issue with sizing the hot water heater for the proposed Grohe shower system. When I calculate the GPM required by the new showerhead / body sprays etc., I come up with a worst case scenario of 10-12 GPM. The existing 32 Gallon oil fired water heater will run out of steam in a hurry. The problem is that the existing water heater is only a couple of years old and replacing it is proving to be an unpopular option.
I am thinking about adding a Bosch Aquaster 250SX in series with the existing water heater so that it is AFTER the oil – fired unit. My thinking is that the Bosch will only be called into service during periods of peak demand and that the oil fired unit will give the Bosch slightly warmer water than comes in from the street. This should give the Bosch a head start on keeping up with demand.
Does anyone have an opinion on this? Are there other options that I should consider? Thanks
Replies
The Bosch will only let about 6 GPM through - if you need 12 GPM, there are going to be some pretty cold showers in the winter.
Different shower head and body sprays?
What size water lines does your house have that will give you 12 GPM to begin with?
The house is fed by a 1 inch line with 85-90PSI pressure. I step the pressure down to 55PSI with a reducer to prevent unnecessary wear on washing machine hoses etc.
You can get tankless, gas-fired units that will heat 8 GPM. Two of them in parallel should do the trick. Don't forget to run a new gas line that can handle the 500K BTU/hr, and that dinky gas meter outside will have to go too.
Isn't it funny how these conspicuous consumption toys always end up more complicated, expensive, and over the top than we planned?
I don't know if your worst case was planning was with wife or girlfriend but either was you are going to have to get water heaters with a minimum of 1" inlet and outlet if you hope to get 12 GPM out of a hot water supply. Then to add 4-8 on the cold side you are pushing a 1" suppy line at it's limits if you have any bends at all even at 90 PSI.
The next calculation you'd better check out is what kind of drain you have that can handle 15+ GPM. A normal 2" trapped shower drain won't. I'd do 3 or 4 if I had that kind of water flow heading down the drain. Even with 3 I'd limit the shower to only bald folks, a few hairs will slow the flow quickly.
Are you sure that this shower isn't a recirculated system? I looked into those prior to my remodel and found that they are really stand up baths. I ended up putting in two sets of shower valves, each running one shower head and two body sprays. 50 gallon water heater on a well at 70psi. Everything going at once will get about 20min maximum. Stand in there all day with just one set going. 2" drain, no problem. Best of luck.
John
That's hard to believe. Are you saying there's a plumbing code that allows recirculated waste water in a shower? Imagine, a $25K shower that washes people with the same efficiency as a feather stripper in a chicken packing plant. What will they think of next?
I guess when you shower with one of those units, you'd better make sure you start at the top and work your way down!
http://www.keidel.com/design/select/showers-carwash.htm
Check out this link. When I researched the top end systems the water requirements were out of sight. Most standard water services and heaters couldn't support them. A plumbing supplier clued me into the sales pitch. When the homeowner was sold on the big fancy shower concept, they come back and say 'to support your system's water requirements you'll need all these upgrades, we can save you all that money by going with the carwash style system'. Now you have what's essentially a stand up bath. The wife and I stopped considering those systems at that point and designed a shower around our home's capacities.
John
A couple of things.
10 to 12 gpm is screamin you must have at least 3/4" pipe. 1/2" pipe at 12 gpm = 9.44 ft per sec & that will tear up your pipe real quick.
3/4" = 5.66 ft per sec & that is the max you want to be.
That tankless has a max flow of 6.35 gpm----- now at 12 gpm you're probably pullin about 8gpm hot & 4 gpm cold give or take a bit.
Two of the tankless in parallel would work but would be really hard to recoup the up front cost of purchase.
Another option is to get an insulated storage tank put on a circ system--- so if you got a forty gal tank then you would have 72 gal capacity--- Pullin 8gpm of you get a 9 min shower----- worst case like you said.
You could turn up the temp on the heater a bit & that would reduce the gpm from the water heater
Just some thing to ponder
What model grohe you lookin at 12 gpm seems pretty high to me