electric water heater for hydronic backup

[barnartist]

It's becoming clear I'll be out of wood late this winter. I also have some away from home time ahead. My family will still be home and I am the sole wood stoker.

What should I look for. Polaris I have heard of. Then how would I need to plumb it in. Thanks!

 

[in hot water]

What supply temperatures do you need? Condensing boiler, or condensing WHs like the Polaris, are most efficient with return temperatures below 130F. If you need 160F or high they may not be worth the extra expense, being a part time heat source.

What are your fuel option electric, gas, oil, LP? Then check the cost per each, including the hidden fees like meter cost, delivery and taxes.

It is not often that you find electricity to be the least expensive, but heat pumps can offset that a bit with high COP. Front end cost of any heat pump will be quite a bit more than and electric boiler.

An electric heat source will be the least expensive to install if you have enough electrical capacity to drive it. In some cases you can get a regular off the shelf water heater, 50 gallon, and replace the elements with higher wattage. Two 6KW elements running together = 40,000 BTU/hr. But it would require two 30 amp circuits.

Maybe on of those heat pump water heaters or the add on heat pump packages may work, watch the output numbers, however.

In some areas cost per KWH drops considerably in the evening, with some storage you could do the same as you do with wood.

There are a bunch of fuel cost calculators online to compare operating cost. Regular gas, oil, LP boilers figure low 80% efficiency, condensing upper 80's maybe 90 if you have a low temperature distribution like radiant floors.

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[DaveBP]

If you're talking about temporarily replacing a 60KW boiler with an electric boiler that will be a project involving some very large wire.

I'm guessing that you won't need to replace the entire max output of the boiler; but estimating how much heat you will need is the first step.

The conventional wisdom that I have been given is that you don't want your backup to heat the storage tank but it might be a good way to run an electric backup. If your tank is in a place that you need to heat anyway, any heat loss from it is put to good use. So using an electric heater to heat your storage tank might allow it to store heat during times of low load and not get overwhelmed during the night. That might allow you to use a smaller electric boiler than what would be required to keep up with the max load on its own.

Just occurred to me that you might be talking about a regular 'ol 40 gallon water heater . That would be a lot cheaper to install but aren't those only rated about 4 or 5 KW tops? They are certainly only about 1/10 the output of your EKO 60 at best. Would that be enough?

 

[barnartist]

I would only need 140 at most supply temps. I only would want to use it during the shoulder seasons, at least most of the time. I dont think I need to heat 1000 gallons of storage for any reason, and I dont think my electric supplier has cut rates at night but I will certainly check. I do have the ability to shut off one of my tanks to only have 500 in storage.
The heater would have to be located next to my storage tanks located 80' from heated area. So as my zones cycle on, they would probably send quite a lot of cold to the heater upon start up. Not sure this is a problem just an observation.

I have the ability to heat my house currently without wood heat by using forced air propane. This would be a move for comfort and what seems to be a more efficient way to heat my home as I am now 85% radiant, but the costs may not really pay off. Id like to learn what it would take.

 

[in hot water]

If you already have the backup furnace, and it is mainly a shoulder season backup, it might make more sense to stick with that. i guess it depends on how much $$ you want to spend for another system and tie in for the additional comfort that hydronics offers? If you have access to the parts you need and have your own labor to add, why not. it will take some more control logic to connect it in, etc.

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