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Mini-Split & Generator vs Wood Stove

Hi,

I'm about to build a house about 8 miles outside of Brockport, NY (near Rochester). The lot has electricity but no gas. I would like to heat my house off mini-splits, and I'm currently having a Manual J done to determine feasibility. The footprint of the house almost guarantees that I will need more than one small mini-split rather than one central unit. I plan on having a backup generator.

Here's the question: Should I put in a wood stove for backup heat, or simply put a small minisplit on the generator?

I have several motivations for avoiding the stove: I currently have no combustion appliances inside the house, and I like that. I don't have a good place for the stove, thought I could make one. The stove puts a big hole in my thermal envelope and requires makeup air. And for the price of installing a stove, I can upgrade my generator.

However, I understand that running a mini-split off a generator is not the most efficient proposition. As it's just for backup power, it seems like an okay tradeoff.

Thanks for your help.

--John

Asked by John Ranson
Posted Feb 17, 2017 10:48 AM ET

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8 Answers

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1.

I should add that the lot has 25 acres of woods, so getting wood is a non-issue.

--John

Answered by John Ranson
Posted Feb 17, 2017 11:07 AM ET

2.

If you're planning on a backup generator anyways and aren't enthusiastic about a wood stove, I don't see any reason to explore the wood stove route. To keep the system simple, what about just having a small plugin space heater (or two) stored away for emergency heat? In a high performance home, a space heater or two will easily keep a house comfortable and be a more predictable load on a generator.

If you had extra money in the budget by ditching the stove, I'd also suggest putting that towards the building envelope versus a generator upgrade. Depending on the frequency/duration of power outages in your area, you may never (or rarely) need backup heat in a high performance home.

Answered by Brian P
Posted Feb 17, 2017 11:19 AM ET

3.

John. How reliable is the grid where you are planning to build? How long might a power outage last? Do you take extended trips during the winter months?

I'm not a fan of combustion appliances, but I think you have to consider the likelihood of a prolonged power outage and the consequences for a home in a remote location.

Answered by Steve Knapp CZ 3A Georgia
Posted Feb 17, 2017 11:24 AM ET

4.

Our neighbor who has lived there for 30ish years says the power is reliable. I have dogs, so I always get a house-sitter when I travel. I feel fairly comfortable with a generator based solution.

I already have a couple space heaters that I could use. Saving money on the generator sounds good to me. The building envelope is already pretty upgraded, so it's money that I get to keep in my pocket, maybe for future solar.

--John

Answered by John Ranson
Posted Feb 17, 2017 11:33 AM ET

5.

I grew up on a country road in Brockport (Town of Sweden); the sale of my childhood home closed earlier this week. My parents lived in that house for 49 years.

Agree with your neighbor's assessment on electricity reliability, in general. However the times the power did fail it went out for multiple days on end, for example during the ice storm of 1991. http://www.twcnews.com/nys/rochester/news/2016/03/3/cleaning-up-after-19...

I can't comment on mini-splits on generators. I am sure there are people on this forum with experience with that configuration. I can imagine there may be need to size for inrush currents etc.

I have been heating with wood for about 7 years now. Two years in the house we recently built in PA (using a masonry heater core from a company in Scottsville) and five years in the "cottage" we rented here beforehand. We too have plenty of wood reserve in our forest land, and I actually enjoy splitting wood for a spell each day; it's kind of zen like. However the day will come when I won't be able to do it any longer, and so we have a full heating system in the new house.

It is possible to install a wood burning appliance and maintain a tight envelope. Our last blower door number was .9 ACH50 and we know it is likely better than that as we didn't realize it was permissible to seal off the HRV inlet and exhaust penetrations during the test. I think what we did right there was to install a good damper on the output of the masonry heater and to also pay close attention to the air sealing around the flue pipe. We had a direct duct for the make-up air originally too, but the route was somewhat circuitous, so we ended up using our mechanical room as the plenum for that feed.

Oh and wood heat, inevitably dirty between cleaning up ashes to tromping into the house with firewood. Only moments ago my wife pointed out a t-shirt with soot stains from when I was vacuuming out the masonry heater.

Answered by Andrew Bater
Posted Feb 17, 2017 12:37 PM ET
Edited Feb 17, 2017 12:41 PM ET.

6.

I heat my house with 2 mini splits when needed...only one in the shoulder seasons...zone 6 ....I have a whole house generator and have had no issues the dozen or so times it has kicked on over the last year and a half...I have a gas direct vent propane fireplace which I use on the rare occasion ,mostly for ambience as it is more costly to use ...regards Bob

Answered by bob holodinsky
Posted Feb 17, 2017 12:52 PM ET

7.

We're in the Town of Sweden too. Just hazarding a guess, but I think we're about four miles from your family's old house.

I'll admit that I like wood heat. Radiant heat is really comfy. It's just not a great fit for our current house design. I think a couple oil-filled space heaters sound like a great option for backup heat, and they definitely don't break the budget.

--John

Answered by John Ranson
Posted Feb 17, 2017 12:53 PM ET

8.

John, I assume you know that your first money should be spent on building a very well insulated (OK, make that superinsulated) house, and very tight with mechanical ventilation, for energy efficiency and interior comfort, winter and summer. Given that, your winter heating load will be very low, and how you heat the house won't matter greatly. The system will be small, whatever it is. Moreover, the house will be essentially freeze-proof. You could go away for a week's vacation in January, have the heat fail just after you leave, and on your return the house probably won't be below 50 F inside. So you could heat with wood if you wish, but I imagine you'd want to rely mainly on some automatic system. Heat pumps may well be a good fit for such a house, and the power they use won't be too much for a backup generator.

For comparison, my house in central NH (CZ 6; roughly 4000 sqft conditioned space, final blower door test 0.8 ACH50) is superinsulated has a two-ton geothermal heating system that keeps the house at temperature in just first stage (best number is heat loss of 19 KBTU/hr at outside temp 0 F. I have a 14 KW standby generator, using propane (a Kohler unit). I haven't yet needed to have the heat pump run while the power went out and thus the standby generator was running, but the heat pump uses just 1.7 KW in second stage (less in first stage = normal), so it wouldn't be a big draw on the generator. I recently had a water valve failure on the heating system, so that for a couple of days I had to heat with electric strip backup heat (COP=1). But that's just a total of 6 KW of power, far less than generator capacity, so by managing power use carefully I certainly could get by in the really rare instance of simultaneous failure of heat pump, failure of external power, and outside temperature about as cold as normally is seen here. Then there is the very small woodstove in the lower level, which by itself can heat the whole house in winter, part time!

So my answer for you would be that a properly designed new house for your location certainly can be heated by mini-splits with standby generator providing backup heat if needed. If you like to feel and watch a woodstove at times, you certainly can install one, with directly connected outside combustion air supply, and not compromise the integrity of your thermal envelope.

Answered by Dick Russell
Posted Feb 17, 2017 8:23 PM ET

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