Want to add an electric water heater (on a timer) in series with my existing gas heater to add capacity during the winter months. Which would be better, gas first or electric? or does it matter?
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Assuming you go with an electric water heater you might want to save some money by not installing a timer. If the water heater is well insulated, an added jacket is cheap and can't hurt, the saving are not likely to save enough to pay for the timer in your lifetime. For vacations the breaker can be turned off.
Normel,
How about adding an "on demand/tankless" water heater downstream of your existing unit?
This would enable you to lower the temperature in the holding tank, using the tankless to just boost the temperature of the stored warm/hot water.
Jazzdogg
If you do two tanks, instead of the tankless, partially depends on price of gas and of electricity. But under most circumstances you'll get better bang for the buck with gas, and since the first tank is taking the temp from ~50's to maybe 110 while the second tank is just maintaining, I'd make the gas heater the workhorse. Focus on temp differential.
If the gas HWH is natural gas, definitely put it first. Natural gas is always cheaper per BTU then electricity. Use the electric as essentially a holding tank only (set its thermostat 10F lower). Those limited times when you overrun the gas HWH, the electric will come on to boost the water by 20 or so degrees (instead of 70-80F) and then for a small fraction of your hot water usage.
Those times when you expect A LOT of useage (house guests, teenagers, etc.), turn the electric's thermostat up a bit. Turn it down again when the guests leave and the kids go to college.
But it will work very well to keep you in a shower for a long time. If there are times now when you go through 40 gallons of hot water, there will be very few times that you go through 80-90 gallons of hot water. And it won't come in quite so cold (i.e not so sudden a temperature drop) because it is blended a bit more and you've got both a flame and an element heating the incoming water. It will, however, take longer to recover (be ready for a hot shower again) because you'll be waiting for the electric to catch up and that takes longer than for a gas HWH. Probably not a frequent issue at all. And if you've stayed in the shower that long, it was time to get out, anyway.
Those times when you expect A LOT of useage (house guests, teenagers, etc.), turn the electric's thermostat up a bit. Turn it down again when the guests leave and the kids go to college.
Just a bit though, safety experts recommend no more than 125 degrees, 120 if there are infants or elderly living there._______________________
"I may have said the same thing before... But my explanation, I am sure, will always be different." Oscar Wilde
Bob: Agreed. However, I always installing tempering valves so one can temporarily crank the HWH and still have 120F going to the faucets.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Just put in a bigger gas heater. Two heaters = 2x the chance of a leak, and 2x the space used up. The electric is lower in efficiency, plus you have to have adequate electrical capacity to run it as well as having to install the wiring to the heater. And how old is your gas unit? If its geting elderly, it may be less able to heat the water due to lime accumulations, at any rate it may be due for replacement.
Not all gas heaters have the same btu input either, so possibly you can get one with a larger btu heater, but a 80 gallon tank would be very large for a typical house, and should serve up all the hot water you need.
Unfortunately, replacing with larger heater is not an option due to height limitation for vent. Plenty of floor space for electric as well as capacity. Will set up electric as second heater as advised above,
Thanks everyone!
I just read through this thread again and offer this:
If using a timer and having the tanks piped in series, I think the gas unit should be closer to the fixtures. If it is maintaining, say 120 degrees, you get 120 degree water initially and the water temp will slowly decrease. When on the electric could start boosting the street water to something other than 50 degrees so the gas unit would not have as big a temperature differential to overcome. When you have the electric dormant the gas unit will perform as it has been, taking 50 degree street water to 120 degrees.
If the electric was closer to the fixtures the gas unit would heat the street water and the electric would be mixing and reheating that same water. When the electric was dormant the tank water temp would gradually decrease and the 120 degree water from the gas unit would have to mix with the dormant electric tank's water thus reducing its temp immediately. (Much like turning on the cold and hot water valve at the shower).
The gas unit should be second (closer to the fixtures) and use the electric to boost the incoming temp when the timer calls for it.
Bill
I had 4 teenage daughters plus wife, a son and myself, all going for showers Friday late afternoon and with me last. I was always with cold water since we had electric 40 US gallon.
Soon as I got the house into our name, in went a single 50 US gallon Natural Gas unit. Never had a cold shower after that day.
At my age, my fingers & knees arrive at work an hour after I do.
Aaron the HandymanVancouver, Canada
"I think the gas unit should be closer to the fixtures" Nope. Electrons cost more than methane molecules. Set it up to use the gas unit almost all the time and very rarely the electric. e.g. use the electric essentially as a holding tank.
"electric would be mixing and reheating that same water" How? Mostly the hot water introduced to the electric would rise to the top. And the operation of an electric, unless it is mis-wired, is designed to maintain stratification of the water with the hot water on top. That ( and recharge ratings and limited amperage) are why the top element comes on first and the bottom element only comes on after the upper water is all hot. But this concern is more completely addressed by putting the electric downstream.
At the beginning of really long, hot and steamy session in the shower, both tanks are hot. With the gas upstrean, its larger heat input starts sooner. All the hot water from the gas unit (40-50 gallons) goes to the electric before it see any cold water. Its volume is still available (50-60 gallons) and its lower element comes on when the bottom half gets cooler. The top element comes on (to heat water that has already seen a gas flame and one electric element) when warm water gets to it.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
David,
This is what he said :"Want to add an electric water heater (on a timer) in series with my existing gas heater to add capacity during the winter months."
I agree that gas is cheaper than electricity, which is why the gas unit should be the primary heater. He want the secondary heater to be on a timer to add capacity during the winter months.
During the summer his intention is to not run the electric at all. If the gas unit is piped first and the electric units elements are off, the water in the "holding tank" is going to loose all the heat the gas unit added. A good bit of that cooler water would go down the drain waiting for the Hot water to get to the fixtures.
If a given amount of water requires a certain amount of heat to raise its temperature 1 degree (what is that measurement?.... a BTU?) it then takes the same amount of heat to raise 50 degree water to 60 degrees as it does to raise 90 degree water to 100. But it does take longer to bring 50 degree water to 100 degrees that it does to bring 80 degree water to 100 degrees. The whole issue he has with his current situation is because of the recovery time in the tank he has (during the winter). The electric would boost the incoming water temp to the gas unit so therefore the tank recovery time in the gas unit would be reduced allowing him to get his shower before dinner.
The system could be plumbed with a bypass to skip over the electric during the summer time but that creates a "stagnant" water situation in the electric which can cause all those nasty Legionnaire's disease issues.
Thoughts?
Bill
Bill: You're right that I've ignored what the poster thinks he wants to do and instead focused on solving the problem. Unless he can get time-of-use electric rates (actually, even if he could) or is required to have an electric unit on a timer (such as in some parts of Germany), I just don't see the advantage of adding the expense and bother of a timer. Just turn off the breaker in the summer, if desired. So rather than think about how to best use a timered electric unit, I've given my thoughts on how to maximize the available hot water while minimizing installation and operating costs.
I am passingly familiar with tanks in series having installed about 80 such set-ups, almost always with an electric unit downstream.
A cross-over pipe with valve would allow the electric to be bypassed easily, seasonally. Note that the electric MUST remain unvalved on one leg to allow for expansion/contraction of the water inside.
I know that Legionarie's has been documented within water pipes, although I haven't seen any authoritive data on Legionaires' in copper pipe (copper is a pretty good biocide). Nor have seen those reporting that Legionaires' has been found in closed piping systems report wether the water was from a chlorinated city water supply, a well system, or in a long-term, closed hydronic loop.
I let some of the loops in my own house go stagant for the 4 months of non-heating season without concern because 1) all the materials are food-grade stuff, it goes in chlorinated, and 3) I'm not introducing any biological active material into the loop. Now, swamp coolers in warm climates and/or ducting systems so poorly designed as to have pools in water in them? Combined with old folks? That would concern me.
Broadly, I'm proposing to give him so much hot water, almost entirely heated with cheaper gas, that he never has to worry about recovery time. Although recovery time would be greatly imroved, as well.David Thomas Overlooking Cook Inlet in Kenai, Alaska
David and BillH - Thanks for your informative posts (as yours usually are). I had originally planned on using a timer because I already have one, but after what I've read here and after giving it more thought, I think putting the electric downstream is the better solution as it will not have to work as hard (= cheaper) if used as a heat booster/maintainer. Whether I pipe in a bypass or not is still a question. I may just leave the thing active year-round and not have to worry about running out of hot water.
Thanks again.