Wintertime Minisplit use article

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peakbagger

Minister of Fire
Jul 11, 2008
8,845
Northern NH
https://www.centralmaine.com/2018/10/28/hot-and-cold-on-heat-pumps-in-maine/

Interesting article I will look forward to the study conclusions. I am somewhere in between and my normal choice of fuel is electric or wood with oil as backup if all else fails. I just have one minisplit on my main floor and need to heat my office in the second floor by convection up a stairwell. I find it works well down to about 30 F but unless the sun is out the heat coming up the stairs just doesn't offset the heat loss. Its not a great setup but hard to justify switching my older office cooling only mini split until it dies. I also run the minisplit off of banked "free" solar power so I don't want to burn my surplus up to early in the season.

I do agree that the way to go in cold conditions with a mini split is set it and forget it. Its definitely takes several hours to warm up a cold house when I am out of town on business for few days. My normal approach is heat up the wood boiler storage before I head out and set back the thermostats to 60 F and then set the minisplit to 64F. That will carry the house for several days unless its really cold (below zero). When I get home I crank up the boiler to reheat the house as the minisplit may take 12 plus hours.

The other issue is if its damp or snowing in cold conditions the coils frost up quicker and that means more defrost cycles which are noisy. Mine is situated on the downwind side of the house well off the ground with roof over it to deflect snow but it its blowing snow it can get frosted up.

I did a recent posting that a family friend that does vented kerosene heaters is getting a lot of calls from folks with minisplits to get their old Monitors repaired or new ones installed for cold weather heating. A minisplit just doesn't put out very warm air in cold conditions and along with the fan running full bore it can get drafty. A Monitor puts out a lot warmer air and can put out more of it when needed.
 
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Interesting article. It makes some good points. They are not the ultimate heating panacea for all situations. Maine is a pretty extreme case. Contrast this to use in mid-Atlantic or Pac NW states where temps are more moderate and the results are much more positive. I visited a neighbor on a rare 14º day. They had a Fujitsu 12000 btu heat pump in their old, small farmhouse. It was doing a remarkably good job at keeping the area in which it was installed at a comfortable temperature.
 
begreen said:
Interesting article. It makes some good points. They are not the ultimate heating panacea for all situations. Maine is a pretty extreme case. Contrast this to use in mid-Atlantic or Pac NW states where temps are more moderate and the results are much more positive. I visited a neighbor on a rare 14º day. They had a Fujitsu 12000 btu heat pump in their old, small farmhouse. It was doing a remarkably good job at keeping the area in which it was installed at a comfortable temperature.
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I have one upstairs and downstairs ( Fujitsu RLS 2- 12k ). If you are used to a wood stove.. it's cool ( Norther Ma). The only toasty place is at the kitchen table directly below the heat pump exhaust. That said.. it is never below 66F downstairs, and though cool, it is not freezing. I used to, sometimes, wake up to frozen pipes

With the old smoke dragon, I had propane for backup, but the unit had all the stealth of a 747 at take off, so I'd turn off the propane for sleep, the fire in the smoke dragon would die out,and the pipes would begin to freeze. The heat pump beat is as quiet as can be

Ah well.. the progress hybrid is still useful for deep warming the bones
 
Just no substitute for good old radiant heat. I have been sitting out in front of a bonfire at -10 F and been hot from the radiant heat and cold at 65 degrees with just convective heat. Most hunting cabins have little or no insulation but crank up the wood stove and it will be warm from the radiant heat.

Maine was pushing minisplits for older folks with not very energy efficient homes. The concept was give them one room that they could heat up with the minisplit during waking hours and keep the rest of the house cold. I expect the thermostats are cranked right up on the mini splits
 
peakbagger said:
Just no substitute for good old radiant heat. I have been sitting out in front of a bonfire at -10 F and been hot from the radiant heat and cold at 65 degrees with just convective heat. Most hunting cabins have little or no insulation but crank up the wood stove and it will be warm from the radiant heat.

Maine was pushing minisplits for older folks with not very energy efficient homes. The concept was give them one room that they could heat up with the minisplit during waking hours and keep the rest of the house cold. I expect the thermostats are cranked right up on the mini splits
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I can believe it at -10. I've had the same feeling sitting in a room away from the wood stove when it's only 20F outside. With just regular R13 insulation the walls are colder and it feels like the warmth is being sucked out of your body.
 
We just (FINALLY) got some splits installed yesterday. Two 12k Daikins. Been wanting these for a long time. I reset my energy monitor, now to see what all the hipe is about. :)
 
Look forward to hearing about your experience with them in Nova Scotia. I ran mine most of this week in place of running my boiler. I cranked up the boiler this morning as the forecast is for colder week coming up plus I needed to charge up my hot water tank as my solar hot water system is at the point where it wont give me consistently warm enough water.
 
Huh yeah, I just lit a fire again this morning because storage temps were down & the splits don't cover the end of the house that only sees use now when kids are home from university. Which they are this weekend.

But that's OK. I should hopefully be looking at fires maybe every 3-4 days until winter really hits, instead of every 1-2 days. It's only been one night, but impressed so far with how far they can actually send the heat out. I was kind of leery about that part. Our house is pretty chopped up so kind of behind an 8 ball there, but it's 21°c in my office which is across the room through a hall and around a couple corners from where one of the splits is. It is 2c, windy with ice pellets & rain outside right now. And most of the night.

My father, just down the hill from us on same driveway, also got one put in at the same time but they ran out of time yesterday to get his up & running. One 15k unit. Really looking forward to what that does more than ours. He uses oil in shoulder season, last month I think it was around $10/day. From poor at times memory. The oil fill pipe is like 15' from the outside unit - imagine the oil man won't appreciate seeing that there next time he fills up lol.
 
peakbagger said:
Look forward to hearing about your experience with them in Nova Scotia. I ran mine most of this week in place of running my boiler. I cranked up the boiler this morning as the forecast is for colder week coming up plus I needed to charge up my hot water tank as my solar hot water system is at the point where it wont give me consistently warm enough water.
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Daikin has been making mini-splits for a long time. I can recall wanting one in 2006, but there were no WA state dealers at the time. Many years back we had someone I think that was from Nova Scotia report on his experience with Daikins. He seemed pretty pleased with it.

Before purchase discussions
https://www.hearth.com/talk/threads/ductless-heat-pump-which-is-a-better-unit.54710/
After installation report. This was a particularly cold winter for them.
https://www.hearth.com/talk/threads/impressed-with-the-daikin-ductless-heat-pump.60963
 
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It has only been a week, and I don't know how accurate this Effergy thing really is, but our two units seem to be usually using somewhere around 8kwh/day total, so far.

The upstairs unit is a floor mount (actually on the wall a couple inches above the baseboard), and I am really impressed with it. It sends heat out the bottom and the top, if you want it to. So some of it actually hits the floor right where wifey steps out of bed in the morning. Seems to run quieter and more evenly/consistently that the downstairs wall mount. It is sending heat across our bedroom, a hallway, and down another one to the other end of the upstairs. So doing the whole upper half of the house. Now, if the kids were home, I would no doubt need to be sending some hot water heat to their bedrooms at times - but they're not, until the holiday season hits. Downstairs unit sends it farther than I was expecting also, but still need some hot water now & again in the far end of the kitchen. Where prevailing winds hit 10 windows and a door all in a row. My office is nip & tuck on colder days - I could maybe use a through wall fan in a strategic location to get the air to go in a full circle through it. So thinking about that.

I would ordinarily be burning every day now. That is down to every 2 or 3. Some of those burns are from wanting to charge everything up with heat (house & storage) in the face of an impending storm - been a darn stormy fall here. One power outage a few days ago, only lasted a couple hours though. One a couple weeks ago lasted a full 24 hours. Had a heavy snowfall warning for yesterday, but it fizzled a bit - thank you very much.
 
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So - what has everyone settled on for their situation, for a 'low cut off' temp, where they will shut the splits down & use something else?

I let our two new ones go all day yesterday, in steady -14c temps, to see what would happen. Unusually cold here for November. They put out good heat all day (a full 24 hours from midnight to midnight), but my monitor is telling me they used an extra 10kwh for the day. Or thereabouts. That's only an extra $1.80 at our rates - but still I don't think I will let them go that low if I can help it, and will build a fire instead. Certainly still beats the cost of oil or our backup electric boiler though. And maybe even wood too if buying it or time is tight.

Also, even with putting out that good heat all day, it wasn't reaching the far end of our kitchen good enough for the heat loss, so I needed to use storage to keep that up. So that means still burning, every other day. We would need one more unit out there to totally cover us with splits.
 
It's very cold back east right now. Heating well at -14ºC is very respectable. Thanks for the update.
 
I find that anything below 20 F overnight I am don't want to put up with the defrost cycles. Sure it will put out heat but the efficiency and output drops. I can run lower but I would rather run the wood boiler. If I leave for a few days I will leave it on down to -5F.
 
Fwiw, making a rough conversion of btus from electricity to btus from wood may aid in determining how low to go with the mini, and also comparing when to use generally. For example, that extra 10kwh for the day equates to about 6 lbs of wood in available btu content. 3412 * 10 / 6050 = 5.6 lbs, or 168 lbs for a month, which is about 5% of a cord of white birch.
 
First post here, but we're having two mini-splits installed in January and I'm curious about the mechanics of what's being suggested by Efficiency Maine in the article in the OP.

My understanding is that the mini-splits start to really lose efficiency in extreme cold at least in part due to their need to defrost. If its cold enough outside that the interior temperature drops to 10 degrees below what the heat pumps are set to (the delta at which Efficiency Maine is suggesting to set your furnace to kick in), why would I want to allow the mini-splits to continue to run, using energy to defrost themselves but no longer contributing to heating the house? And all to have my home 10 degrees colder than I want it?

I am honestly confused and feel like I must be missing something.
 
'For backup'. The implication I read, is if the temp dropped by 10 (or whatever you use), it is because the splits stopped running for some reason.
 
rowan_cb said:
First post here, but we're having two mini-splits installed in January and I'm curious about the mechanics of what's being suggested by Efficiency Maine in the article in the OP.

My understanding is that the mini-splits start to really lose efficiency in extreme cold at least in part due to their need to defrost. If its cold enough outside that the interior temperature drops to 10 degrees below what the heat pumps are set to (the delta at which Efficiency Maine is suggesting to set your furnace to kick in), why would I want to allow the mini-splits to continue to run, using energy to defrost themselves but no longer contributing to heating the house? And all to have my home 10 degrees colder than I want it?

I am honestly confused and feel like I must be missing something.
Click to expand...

Its not really that the defrost cycle is eating up a lot of power as much as there is less available energy in the outside air that can be moved indoors as the temps drop. As the outdoor temps drop you need more heat to keep the interior of the house warm and conversely as the temp drops there is less heat available from the heat pump. At some point the heat required to heat the house exceeds the capacity of the heat pump and the interior house temps start to drop.

I agree with Efficiency Maine to set the heat pump and forget it with two big conditions. If the house has an automatic backup heating system and if the outdoor temps exceed 10F. I have intentionally tired to run my house on a mini split down to -10deg F and its not worth the power and the drafts caused by the fan actually makes me want to increase the temperature setting.
 
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peakbagger said:
Its not really that the defrost cycle is eating up a lot of power as much as there is less available energy in the outside air that can be moved indoors as the temps drop. As the outdoor temps drop you need more heat to keep the interior of the house warm and conversely as the temp drops there is less heat available from the heat pump. At some point the heat required to heat the house exceeds the capacity of the heat pump and the interior house temps start to drop.

I agree with Efficiency Maine to set the heat pump and forget it with two big conditions. If the house has an automatic backup heating system and if the outdoor temps exceed 10F. I have intentionally tired to run my house on a mini split down to -10deg F and its not worth the power and the drafts caused by the fan actually makes me want to increase the temperature setting.
Click to expand...

Yes.

I also agree with set & forget, but I would use less than 10°dT between systems. I would close it up a lot, actually, maybe only a couple of degrees. So maybe more like 68°f oil stat (if you have oil), and 70°f splits. Once you get the right dT derived for your house & climate & systems, it should all be fully automatic - when the cold makes the heat loss greater than the splits can easily keep up with, the inside temp will drop those couple few small degrees, then your other system will kick in and help. Or take right over if it's really cold out & the heat loss really takes off. When the other system kicks in, it might keep the temp up above what the splits are set for & they might not kick on at all, until it warms back up again. A bit of a balancing act - individual stat differentials could also be adjusted. Or just shut the splits off or turn the oil stat up while it's real cold out if a balance can't be struck.

It's been a bit over a month for ours, and I think I am settling on somewhere between -5 and -10°c for when I get the wood fire going. But it varies, depending on who is here and the mood I'm in. Kids are home from school for the holidays, so wood fires are steadier - their end of the upstairs is the place least covered by the splits. If I didn't have wood and only had say oil, I would run them down a lot further. To -15c at least. And likely add a third unit. Still cheaper than oil at that point. Father put one in at his place at the same time, a 15k unit. It's been running steady since. His monthly oil bill dropped from $250 to $180 from 3 weeks (stormy & cold weeks) of split use in November. Electric bills haven't shown up yet.
 
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I am about to install one of these off brand Poineer units. I can buy 5 of these units for the price local companies want to charge to install name brand units in comparable size. My cousin is a hvac tech with all the proper tools such as vacuum pump, nitrogen, gauges, etc.

This $918 pioneer unit is rated to -13 and puts out its full heat down to 5 degrees. Has a HSPF of 11.2 which is pretty good. They get remarkably good reviews and the company selling them seems to honor the warranty and send out parts if needed.

Im just expecting it to last the 2 years parts and 5 year compressor warranty for the price. I could still buy 4 more units with the money I saved if it blows up. Reinstalling one of these would be simple since everything else would be in place such as pad, electrical, hole in the wall, etc.

Researching online these are really not hard to install with a good vacuum pump, micron gauge, and valve core removal tool.

https://www.pioneerminisplit.com/co...lit-air-conditioner-heat-pump-system-full-set
 
Installed cost here for the Daikins worked out to about $3500/unit. Canadian. That got peace of mind with a pro install and 12 year parts & labour warranty.

If I had an HVAC buddy with all the right tools who offered to do that work, I might consider a DIY. Aside from the refrigeration aspect, and a bit of electrical, it isn't all that bad a job. There is a technique to getting it to look right with all the proper shrouding components & that kind of thing. And proper stands. Miscellaneous stuff that is extra in a DIY case. But not having any or much warranty when all said & done would kind of bug me over time.
 
I am surprised that the 12000 btu unit is 120 volt. Most of the others of that size are 240 volt.

I agree that you are going in with eyes wide open and know someone that has the tools and the skills to swap out a unit that its a tempting proposition. I seriously doubt that the unit is serviceable if internal components fail.

I would suggest going to supplyhouse and buy the "gutter" system used to protect the line sets between the outdoor unit and the indoors.https://www.supplyhouse.com/Line-Set-Covers-17880000, Your choice on what brand.

I also suggest a surge suppressor on the circuit as I expect the electronics may not be very tolerant of surges.
 
Got our power bill yesterday.

It was for a 61 day period, our splits came on line on day 18 of that. Bill was around 500kwh more than would have been typical otherwise. At 0.18/kwh, I am estimating they cost us around $2/day. There were a few days they didn't run, but also a few where I ran them at colder temps than I am doing now.

We were away over Xmas, for 4 days. Will be on the next billing period. It was kind of cold while gone, -6c days (but sunny), -12 to -14c nights. The Effergy showed about 25 kwh/day more than typical. But not sure how accurate it is.

Sure as heck beats the electric backup boiler at like $25/day.
 
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