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DArndt
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| Joined: | Wed Mar 26th, 2008 |
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Posted: Wed Mar 26th, 2008 09:48 pm |
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I'd like a reaction to how small a water heater would work ?
Two people, 60+
There is a dish washer, clothes washer, shower.
Input is well water.
Only one item in use at a time, allowing for recovery before next use is ok. but must satisfy a single use.
Now I expect most people aren't going to answer the question, but instead ask me why, so here goes.
I have a summer house, (system drained in winter) we use for two weeks, then gone for two weeks. Currently, 50 gal, electric HW heater in basement, apx 60 degrees, well water (cold). Every time I leave, I turn off the HW, when we get back, it's cold and has to be reheated. Meaning, I lose 50 gal of hot water each trip. What I'd like to do is add a small heater after the big one, and leave the big one off. However, when there are more than just the two of us, then I'd turn on the big tank.
So, would a 10, a 15, a 20, work in this situation ?
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Ej
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Posted: Thu Mar 27th, 2008 01:34 am |
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| Quick rule of thumb, you will only get 2/3rds of a heater's capacity before it starts to drop 15-20 degrees. With your 60 degree well water I would say this would be even less. The smaller tank sizes you list are normally for single use purposes. A 30 gallon heater would be the smallest I would even consider. Check your gallons per minute usage on shower heads, washers ect. and see what your needs require.
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DArndt
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Posted: Thu Mar 27th, 2008 03:48 pm |
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I forgot to mention, the shower has a low-flow head.
Since we can easly control the functions (don't take a shower if either washer is running, and don't run both washers at the same time) this really comes down to "single use" mode.
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energyexpert
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Posted: Tue Apr 1st, 2008 11:30 pm |
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What is the hot water flow requirement over time? A 2 gpm shower head uses 20 gallons in 10 minutes. A washing machine typically draws 5+ gpm.
Recovery is the next issue. 4500 watts will heat 20 gph 90 F rise. (or 30 gph 60 F rise. 50 F inlet and 60 F rise yields 110 F which is OK for a shower)
But if you empty a 30, can you wait 40 to 45 minutes for recovery? If not you need larger storage or more output. If you can get a separate circuit to the WH, you can change out the lower thermostat for another upper thermostat and wire the lower element independent of the upper. This gives you twice the recovery.
David
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DArndt
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Posted: Wed Apr 2nd, 2008 04:49 pm |
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Tankless heaters have a "flow" rating, ie, they can maintain x temp at y gph. Now if we had a similar value for a "tanked" heater we'd get somewhere.
Assume a shower is 2 gph, however, that's not 100% hot water, so the hot component is less. Also, recovery figures assume a "batch" function ... empty tank, replace with cold water, turn on heat. But, actual use doesn't work that way, water starts out hot, draw some out at a specific rate, and cold water enters, cooling the remaining water until the low temp value is reached, then the heat turns on. so at this point we have cold water coming in, and heating element applying heat while we continue to draw "hot" water out. That's where I refer to the "flow" rating, at what gph draw would the tank "balance" ? (of course, water temps in&out are needed) or if not balance, at least what would the temp drop rate be. So, a shower at 2 gph, is using less than that rate due to cold water being added, as the temp drops, you keep reducinging the cold until you're 100% hot, that's about the total length of time you really have. as from that point on, it's just going to get cooler.
The real trouble is, the smaller tanks also have slower recovery rates too. Don't know why we can't have the same heaters in a 50 gal tank, in a 20 gal one. Sigh
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Ej
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Posted: Thu Apr 3rd, 2008 02:19 am |
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| It sounds like you should perform a test with a 2 gallon bucket, a thermometer, and a kitchen sink faucet. This should answer some of your questions.
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eleent
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Posted: Thu Apr 3rd, 2008 05:43 am |
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Hello: Looking at my Rheem book, I see that from 30 to 80 gallons all their heaters have the same 21 gallons per hour recovery with a 90 degree rise. All the heaters use a 4500 watt element. It might be worth a call to Rheem to see if you could put a 6000 watt element in a 30 gallon heater to speed up recovery.
Yours, Larry
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RKG
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Posted: Sun Apr 13th, 2008 03:16 am |
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For what it is worth:
On my boat, we have a 110VAC 1800W hot water heater, which is used only when operating on shore power. The heater is made by Atwood and holds a nominal 6 gallons.
This probably qualifies as pretty small.
We have no trouble taking two back-to-back showers (bearing in mind that these are "Navy showers").
I have no doubt the heater would handle a dishwasher load.
I have no idea whether it would handle a clothes washer load.
Last edited on Sun Apr 13th, 2008 03:16 am by RKG
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