multiple water-heater instalation

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by rrich4814, Apr 19, 2008.

  1. rrich4814

    rrich4814 New Member

    I'm needing to install multiple water-heater system for more gallon avaliablity for a 4-shower 4-sink restroom. Tanks are electric 80 gallon. I thought about piping them in series but what would be your suggestion as I need lots of gallon and the quickest recovery. The senerio is 40 potiential people using this room at any given time.
  2. Basement_Lurker

    Basement_Lurker One who lurks

    Victoria, BC
    Hmm I don't think electrics would quite cut it for that much usage.
  3. probably wont work

    you might be beter off to pipe two showers to one 80 gallon electric and two to the other electric heater and set the temps up a little higher......

    if you have 40 people wanting to take showers all at the same time that is a rather crowded bathroom....

    the only way you even have a chance to keep up with the demand is to put in some shower heads with very tight water restrictors in them

    Also get Delta 1700 pressure balanced shower faucets where you can set the inernal heat on only lukewarm to med ...
  4. Cass

    Cass Plumber

    If your water is soft you could try using an electric tankless heater in conjunction with the 2 heaters, depending on the SFR for the heaters it might work, but you will need more power.

    You might use 2-3 electric tankless heaters. You must have soft water and lots of power.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    Series would give the most reliable maximum capacity, but your demand would be limited by the 3/4" inlets and outlets. Pressure balanced shower valves would minimize the impact, but when all the showers and sinks are being used simultaneously the flow for all of them might be reduced. It might be better to use each heater for a specific shower, or showers, and not try to get all the heaters to feed all the showers.
  6. Bob NH

    Bob NH In the Trades

    New Hampshire
    Figure out a schedule for shower usage. You will have 4 showers. If 40 people are using them, how many showers in the peak hour? What fraction of the time is the water running?

    EXAMPLE (You must do your own)
    Assume that each shower takes 5 minutes, and 5 minutes to clear before the next guy turns on the water; so you have 50% water-on cycle.

    If each shower takes 10 minutes you can get everyone through in 100 minutes.

    Each shower uses 2.5 GPM when running and you are using 12.5 gallons per shower, so you will use 500 gallons of hot water. Add 1 gallon per person at the sinks to give you 540 gallons.

    Feed water temperature (winter wells) is 55 degrees F, and shower temperature is 120 F, for a 65 F temperature rise.

    Two 80-gallon heaters at 150F settings will produce 234 gallons of 120 F water, so you need to add 300 gallons of recovery in 100 minutes.

    300 gallons x 65 F temperature rise x 8.34 # per gallon / 100 minutes = 1626.3 BTU per minute = 97,600 BTU per hour. That is a bit more than 28 kilowatts, or about 120 Amps. Too much for MOST instant water heaters.

    That may not be enough because the heaters won't come on and run continuously. To be safe you should have a recovery rate equal to the peak demand. At 5 GPM which would result from a 50% duty cycle on 4 showers, you would need 163,000 BTUs per hour.

    You could do it with a couple of 80 gallon propane-fired high-recovery gas heaters.

    Do your own numbers. If you have a system where people get out of the shower area quickly so there is only a minute or two between turning the water off and the next one turning it on, then you will need a higher recovery rate.

    Series connection is easy to control but may not work for you because you will want all of the firing to be working when demand is high. Therefore, you will probably want to figure out how to get them all working at the same time when necessary. Some kind of temperature control system, or one very high rate institutional heater, might be the best solution.

    The heater at the link would probably work but I don't know the pipe sizes. And they are not cheap.

    Someone on the forum might be able to suggest a more economical solution.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    In a series configuration ALL the heaters will be working at anytime the temperature in all the tanks has been reduced. Under minimal flow only the initial ones will have to be activated to restore the total temperature to the system. There are lavatories involved, and setting the heaters to 150 degrees will be a good way to land up with a lawsuit when someone burns themselves, at the sink, or even in a shower, (they can get scalded or trip and fall because of thermal shock), before they can turn on more cold water when the maximum hot arrives at the faucet.
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