We have a Mitsubishi hyper heat as our only real heat source. It was working hard Friday evening but our house was still warm. Sometime Friday night it stopped running. The unit is rated down to -25C/-13F and it got colder than that. It ended coming back on Sunday when temps got up to 0C/32F.

We've had the unit for 6 years and are still happy with it. Since our house is very well insulated (HERS score in the 20s), even with no heat for a day and a half, we ran a small ventless propane heater in the basement and a couple space heaters in the rest of the house which kept everything around 13C/55F.

If the house were not as well insulated, I'd be more hesitant to have the heat pump as our only heat source.

We're not sure what caused the shutdown (some internal protection switch or something froze). A tech was able to make it out on Saturday but couldn't find any issue. I'm fairly certain we've had a cold night like that before, but IIRC we ended up turning off the heat overnight so it didn't need to struggle and let the house drop 10 degrees or so. In the morning the heat started right up when we turned it on.

I have an LG mini split system as my only source of heat. Outdoor temps went down to -18 with wind chill of -39 here and I had no problems at all. This is the second winter with these and last year also went down to -15 at least once and it was fine. These units are rated to -13F. When it gets down below zero they work harder but they still provide full heat. I turned them up to 74 on Friday and by Saturday morning I noticed the bigger unit, that had a much bigger area to heat, only kept it up to around 70, but that’s more than enough. I assume the larger indoor unit shut off occasionally as the outside unit probably couldn’t produce enough heat to keep sending hot air in and the inside unit shut off to avoid pumping in cold air, but I don’t know anything about them really and that’s only a theory. In any case, 70 degrees indoors when the wind chill was -39 outdoors isn’t bad at all I’d say.

Mitsubishi hyper heat was blowing hot air the entire time. About as efficient as a regular electric resistive space heater at those temps though.

Had a new Fujitsu Xtra Low Heating mini split single zone installed back in August that said is capable of heating to -15F. Outdoor thermometer was showing -12f at its lowest and its still was blowing warm enough air. Don't think my boiler ever kicked on (Have that set to around 60f).

It's designed to do that below operating temps. Bottom of page 10 in your manual.

This was the first time I've hit the limits on mine, but still see them as the best investment I've made in our house by a lot and really don't regret going hyper heat at all.

Our house still has legacy heating, so we were fine this weekend, but anyone concerned with this kind of setup exclusively could cover these edge cases with a space heater or two as a temp setup.

The rating I was referring to was the "guaranteed operating range" of -25c to 21c on that page.

We dropped below that on Friday. The tech that came out said he was getting a bunch of calls with the same problem.

It wasn't all of them, but does seem to confirm that the -25C threshold is when the probability of failure increases.

Not sole source of heat, but my Bosch BOVA operated down to -12F (its rated to -4F).

Cooper and hunter newly installed, had no issues Friday into Saturday.

Are small mini split type heat pumps really more cost effective given electricity cost vs. other fuel types (oil/propane/gas)??

Right now natural gas can be tough to beat with a heat pump, especially when it's really cold out. OTOH, heat pumps are usually cheaper to run than oil or propane, even with today's higher electricity costs.

This website shows how much it costs to heat your house with various fuels given current prices (Look at $/MBTU for comparison)

https://www.energy.nh.gov/energy-information/nh-fuel-prices

The key is to know the heat pump's coefficient of performance (COP) at various temps. COP tells you how much more efficient a heat pump is compared to using a resistive heating element. A heat pump running at a COP of 2.00 costs half as much to run as a heating element. A heat pump running at a COP of 3.0 can heat your house for a third as much as using resistive heat.

Here's a data sheet that shows real numbers for capacity (btus/hr) and for efficiency (COP) for a modern low temperature heat pump at different temperatures (see table on right):https://ashp.neep.org/#!/product/34469/7/25000///0

Did you notice a big capacity drop off below 0?

We had a Bosch BOVA system installed this year and are very happy with it. But as expected, it had some trouble keeping up once the temp got down to 5 or 10 degrees. (it still was putting out lots of heat but apparently not quite enough).

I had the thermostat set up to switch over to oil at 5 degrees, so I don't know how low it could have run or how much heat it could put out below zero.

Again though. This is about what I expected. The Bosch Specs say our unit goes from around 38k btus of heating at 47 degrees, to 28k at 17, down to just 23k btus at 5 degrees.

https://ashp.neep.org/#!/product/66146/7/25000///0

Can you have a heat pump installed and have natural gas burner at your house? Kind of like play which ever one is cheaper or functioning based weather outside? My house is 25 years old. Not sure how well insulated it is. Would be nice to be able to rely on whichever source happen to be cheaper at the time as well as switches to the other if Temps dip into the negatives.

Yes. You can definitely do this. Gas heating costs can be tough to beat at lower temps, but above 25 or 30 the mini split is likely a slam dunk and that covers a lot of winter hours. The only trouble is that heat pumps can be kind of expensive and the cost might be tough to justify if you only use it a little.

OTOH, with the new heat pump rebates in the Inflation Reduction Act (IRA), I think it might always make financial sense to go with a high efficiency mini-split heat pump over of a plain mini-split AC. The heat pump rebate should more than cover the additional cost of the upgrade.

The numbers quoted "feel" right for capacity. I'd say below 17F is where I start to see a noticeable drop in capacity. Anything above that and it has no issues covering the load. Fortunately, the heat pump is the upstairs zone and the downstairs is still forced hot water (oil) and a pellet stove so the coldest days I overheat the downstairs zone to makeup for the dip in capacity.

The lowest COP you will get out of Mitsubishi hyper heat unit is still 1.8x better than resistant...

Wow. I didn't realize they could get that good of a COP at such low temps. This tech continues to amaze me.

It's way more efficient to move heat than create it...:P

Mini Split (2) mitshubishi hyper heat. Both felt warm to the touch firday night, but around midnight bascially stopped blowing air. They kept looking and sounded like they would begin blowing strong but didn't most of the night.

For anyone who was happy with their install, would you mind sharing who you used? I’m located in the concord area and would appreciate any recommendations. Thanks in advance.

Ask again when they get their bill.

Ive got a Mitsubishi and turned it on for like an hour just out of curiosity once we hit -20. Worked like a champ. I've got a wood stove that works great fortunately so I didn't run it too crazy.

I have a multi head daiken ran just fine.

We had a hybrid system from a company in Nashua. It would automatically switch from heat pump to oil at a predetermined temperature. I think temp was in the teens a few years ago. Very happy with it.

The good news, it can only run a hundred percent of the time. Hopefully you make it back the other 98% of the time.

I have a Fujitsu. It was operating fine for the cold weekend- except there was a small instance right when it hit around a -35 (windchill) I saw a red light blink for a few minutes on the wall mount then it went away. I have no idea what it meant, but my home stayed warm. Kept it at 72 from Thursday to Sunday. I haven’t seen the red light since. I do have baseboard as a back up, but I use my mini split only. Anyone know what Fujitsu is temp rates at? It’s an older model (at least 4 years old) is all I know about it

Mine shutoff around 0 degrees. Noticed temperatures were too high. Not used for my main living area. Just used for… basement activities…

I’m glad it worked out for you but I don’t think I’d be brave enough to not have a oil, propane or wood backup to a heat pump system.

I’d look at alternatives regardless of if you decide to go the heat pump route or not

Personal experience: bought my house ~2 years ago and used a little under three tanks of oil for a heating season. Installed a pellet stove this past spring, which I mainly use for heating the home, and haven’t hit half a tank used yet

The pellet stove is paying for itself way earlier than I anticipated. I’m sure people who converted to heat pumps/stoves can say similar things

I thought they switched to resistance heating if it gets cold enough. Compared to normal operations, that's running way above 100% in terms of electric costs.

Yes, I have the "Kumo Station" on my Mitsubishi hyper heat system. It can control up to 4 zones of backup heat. You set which heat pump zones are backed by which backup zones. Then you set two temps. Above temp A, the backup never runs. Between A and B, heat pump runs first. If it fails to hit set point for the configured delay time, it adds the backup heat. Below temp B, it goes straight to backup heat.

The system works great. I first installed it in my Massachusetts house, because you got huge rebate. It went from $400/ton to $1600/ton by adding the integrated control system. Rebate change more than paid for it. The heat companies charge a bunch for it and some of them don't understand it. When we put the mini-splits in the NH house, I just bought the kumo station and installed it myself.

Heat pumps beat oil pretty well in the shoulder seasons. When it's like 45-50F outside, and they run at low load, they're crazy efficient.

Most heat pumps on the market today will beat oil at temps much much lower than 40 degrees. That 40 degree cutover number is from heat pump technology over 5 years old. The industry has really improved low temp efficiency a ton in the last 5 years.

My Bosch unit (installed in 2022) runs with a COP of 2.4 at 5 degrees. With that COP it's still cheaper than oil to run. As temps go above 5 degrees into the 10s and 20s and 30s, it becomes significantly cheaper than oil (as much as 1/2 the cost at higher temps).

Most current Mitsubishi mini-split models, even the non-hyper heat ones, maintain a COP around 2.2 down to 0 degrees or so. At temps above 10-15 F, they're often closer to a 3.0 COP and some make it close to a 4.0 COP in the upper 20s and 30s.

Yeah, they beat oil at the lower temps, but they absolutely wipe the floor with it at the higher ones. COP at 47F on some of the newer LG systems is pushing 6! It's better at 10-15 than I realized though, thanks!