Tankless water heater, Electric vs natural gas

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powersro

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Hi,

I'm building a summer home in the northeast. I have natural gas available but I'm wondering if an electric tankless water heater is efficient enough to overcome the added cost of an exhaust system for a gas tankless. As an added benefit the electric could be put about 15 feet closer to the sinks. etc. allowing for a quicker access to hot water. Again the home would be May to September so if I go with electric how many KW's would be recommended for twp people in a two bedroom, one bath house?

Any opinions would be appreciated.

Bob
 

Jadnashua

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One Kw=3412BTU.

One BTU can raise one pound of water 1-degree F.

Say your incoming water was 50-degrees and you wanted it 120, that's 70-degree rise. Say you wanted 4gpm, that's 240gph*8.4#=2016 pounds of water to be heated and that *70 degrees =141120BTU or 41.36Kw. At 240vac input, P/V=Amps or 41360/240=172 Amps. Do you really want an electric tankless? A good sized NG tankless is in the order of 200K BTU, would maybe require an upgraded NG supply line or meter or both, but would handle your needs.

The least expensive option would be just a stand alone tank system. There would be more to drain in the winter, but it wouldn't need maybe annual services like a tankless system would to remove the mineral deposits. With the newest versions, they're pretty well insulated, and don't have a lot of standby losses.

If you would be happy with a really low-flow shower head of say 1gpm, and forever to fill a tub or washing machine, yes, you could live with an electric tankless. Most people are too spoiled to accept that.
 

Jadziedzic

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If by "Northeast" you mean somewhere in New England, keep in mind the cost of electricity up here is pretty high - $0.176 per kWh in New Hampshire - and probably destined to increase. Liberty Utilities has some decent rebates for condensing or tankless water heaters ($500 and $800 respectively) which would help with the cost differential. You should also check into the Energy Star program Web site section on "new homes" - there are significant rebates and incentives shown there.
 

Dgeist

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If you're happy with using NG, then check out the condensing models available. Many do not require anything more exotic than solid-core PVC for venting. Also, you'll have to have a gas line that can deliver a lot of volume fairly fast (probably not an issue if this is new construction, but something to think about). I've been very pleased with my unit which is a southeast-asian manufactured marketed by one of the larger american conglomerates under several brand labels. It's vented (intake and exhaust) with 3" PVC to an existing "foundation vent" for which I made a blocking plate and installed simple bird screens on the outside terminations.

Now, the eco-purist will say that the raw energy conversion is more efficient with electric, but as mentioned, gas does heat faster. I also like that fact that with a small battery back-up on a gas-fired system, I can still use hot water in a power outage (also a plus for a tank system, actually, although I generally don't like tanks for other reasons).

15 feet won't make much difference if you insulate your pipes well except for perhaps the first time hot water is used in the AM (a few seconds longer wait).

Dan
 

Craigpump

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For what it's worth, I've got a customer with an electric tankless water heater, he said if he had to do it again he'd go with propane.
 
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