I can’t seem to edit my post to add: I tried to call my installing company but they have no one to talk to unless it’s an emergency. I suspect many of them cannot even get to work right now. thanks!

It shouldn't harm it to turn it off but it won't be running very efficiently at those outside temperatures. You have two choices: 1. run it and it will undoubtedly use the auxiliary heat; 2. turn it to emergency heat and run the backup heat strips only.

Thanks, I don't have any of those things, I don't believe (maybe emergency heat, which I don't need, as I have a woodstove). The unit itself is a mini-split and has no auxiliary heat. I installed it mostly for the air conditioning aspect, which I only use rarely. I don't need to run it for heat during the cold snap, I just didn't want the unit to freeze out there if it's not turned on.
I did check to make sure it wasn't covered in snow or ice, and it's not.

Are you talking about a mini split (with a separate exterior condenser unit) with an interior piece that's floor mounted? Is there an outside part of it that looks like this?

Your operating manual should tell the safe outdoor temperature range for operations. If it's a minisplit, some can continue to produce heat at surprisingly low outdoor temperatures.

Few things are hurt by being turned off.

I’ve never had a problem with turning mine off. I turn mine off when the temperature drops below their efficiency point. I was warned when mine were installed, however, to make sure the fans were cleared of snow after a big storm so they wouldn’t be trying to move air when blocked by snow or ice.

Thanks,pds, that is helpful. I figured it probably was ok, but hadn't been able to confirm that. If it's a problem, it's probably too late because it's been off for 2 days. I did make sure there was no snow or ice in it and will do that again when the temps rise and I might want to use it again.

Typically shutting things off, not using them isn't going to damage them any more than via use.

However, they are still connected to the electrical grid. Nasty weather can pose all sorts of trouble to the electric grid in which they are attached. Power outages, brown outs, electrical surges are all part of that. I've never once said you're unit is dead because it froze to death last winter. ha-ha. --- so it's not the cold that does it if you catch my drift. Maybe indirectly if your unit contains a bunch of plastic. Like plastic fan blades and such... the cold / hot / cold / hot will make plastic brittle over time. Mini splits are known for plastic parts, and there you go.

If it just sits there for 5 years with no use at all, that doesn't mean necessarily that it gain an additional 5 years in use because it just sat there and wasn't used. Can't tell you how many times I went to homes in which the house had more than 1 system, the owners says "how can that other system be broken? we never use it..."

It was a million to one shot doc, a million to one...

Thank you, Austin Air, lol. I was worried about it freezing to death - exactly! I don't know if there are fluids or what that make it work and was worried if they didn't circulate or something, they'd freeze!
I don't know if the Mitsubishi has plastic parts on the exterior unit? Hopefully, it's new enough to not be brittle or deteriorated. It doesn't get direct sun. I seldom use it; just installed it when the PNW started having such devastating air quality from forest fires in the summer and I could no longer open my windows on summer eves to cool my upstairs bedroom. I'm right on the saltwater, so get a nice cool breeze even on the hottest (well, our old hottest nights, not last summer's 110 plus) nights. But if the air is so smoky you can't breathe, cool air is the least of our worries. So now with the mini split and an air purifier, it's bearable. I had it serviced the first year and will again before summer, but he said it got so little use I could skip annual service and go for every 2 years.
I appreciate your expert response; I'll quit worrying. It's slowly warming up to the low 30's so I will use it again soon.

Olychick,

Yeah they have coolant but these are chemicals that don't freeze inside the system they simply change state from gas to liquid. The freezing often noted is exterior ice usually due to freon leaks or lack of maintenance type issues when it comes to cooling or AC mode. If it's a heat pump and you see ice on the outside coils that is a normal function of a heat pump running in heat pump mode that hasn't entered defrost yet. Due to the nature of a mini split and the plethora of controls on these units it's not likely to ever see any ice on them from running in AC mode.

Living near saltwater that will likely kill your system faster than the cold. Saltwater is corrosive in nature, typically it will eat the exterior coils of the unit and if it finds a way indoor, the indoor coil as well.

You can minimize that saltwater problem with regular maintenance cleanings of the equipment. It's in your best interest to hire professional HVAC service for that. That said, saltwater corrosion takes time. It's not an effect that happens over night.

Thanks so much for additional info! I'm on a small bay of Puget Sound and the saltwater corrosion is minimal in this area. Not like on the ocean...and I am far enough away that there is never any mist coming close to me at all. Nothing has ever been affected by salt air here.

I am adding this just for others who may run across this thread. It's part of what I posted on another thread about ductless mini-splits and I'm sure is old news to the pros and experts here, but might be helpful for other homeowners.

"I saw things that said below 40f heat pumps aren't really energy efficient and recommended using auxiliary heat sources. Some nice people here answered my questions and allayed my fears about damage to the unit from extreme cold - even if I didn't use it.

But today when I talked to the Mitsubishi rep, he said that the mini-splits are (at least these models - which he termed Hyper Heat) designed for more extreme cold than regular heat pumps and are efficient down to about 5f."

which he termed Hyper Heat) designed for more extreme cold than regular heat pumps and are efficient down to about 5f."

Yeah some machines even go negative a bit. I've seen some go down as low as -5F. These are inverter machines (Inverter Heat Pumps) , which are the stallions of the HVAC industry. It's where everything is going and for good reason.

Hyper Heat term was designated by Mitsubishi, because heat pumps of old got a bad name as the temps drop outside. That term cuts to the heart of trying to explain what it is.

I have a Bosch Inverter heat pump at my house but it is traditional split ducted, not a mini split. It cranks out the heat -- (so hyper heat is a good term to describe these if on electric heat), but more importantly for me it cools like a beast too.

The Bosch Inverter is still in very tight supply, but I managed to install one a few days ago for a customer of mine.

Inverter essentially means many different speeds the system can run in. Where as HVAC systems before would be either on or off.

He did write that they were 100% efficient down to 5f, so I assume that even below that temp, they will still provide heat but just less efficiently.

yeah I think so, it never gets cold enough here for me to test that theory. ;-)

I have read about heat pump inefficiency in frigid temps so turned it off and am using other heat.

What is your other heat source? The efficiency (electric power per unit of BTU) of a heat pump decreases as the temperature drops. But it may still be more economical to use than other heating fuels.

Good point mike. I have a friend that recently installed a heat pump central system in her 1,000 sf home; new ductwork, electrical panel, the whole works. Previously she'd heated with a couple of propane space heaters and/or a wood stove. Air conditioned with 2 window units. A $25k upgrade in total, I believe she said.

She said the installer told her to turn it off and use her propane heater "when the red light came on". (electric strips)

I told her she'd need to compare kwh cost to propane btu $ to make that determination.

It got down to 20 degrees here last night. I'm interested to learn if the red light came on or not.

If they can make ductless heat pump systems that are 100% efficient down to 5F, why can't/don't they make ducted central systems that are? Or do they and they are just more expensive or what?

If they can make ductless heat pump systems that are 100% efficient down to 5F, why can't/don't they make ducted central systems that are? Or do they and they are just more expensive or what?

They do, but they are inverter. (same as ductless) Inverter is a technology that allows the compressor of the heat pump to run at many different speeds. My Bosch has more than 50 speeds.

If it's not inverter then it's >> traditional heat pump single speed or 2 speed and those will lose performance in heating mode once the temps start falling below 35F, once below 30F outside a traditional heat pump performance goes down hill rather quickly as temps drop.

Not all equipment is created equal, is about the easiest way I can say it. If you live in a warmer climate a traditional HP may be fine. But an Inverter HP in AC mode works better there too.

People and money, money and people. Inverter's cost more, but pay you back over time thru reduced utility bills. Even with that, some people still choose the el cheapo vs the Lamborghini

To me, it doesn't matter. As long as you buy something ;-), I don't care it's your choice not mine. I work on all of them. They all break. That being said, I know you'll be happier with the Lamborghini. Every month the electrical bill comes, smiles.

Thank you so much for the education! I'm old enough that I won't ever have a need to put it to use, but I'm sure others finding this thread will appreciate your response.

If they can make ductless heat pump systems that are 100% efficient down to 5F, why can't/don't they make ducted central systems that are?

I am not sure what you mean by "100% efficient". Heat pumps are air conditioners running in a reverse cycle. They extract the outdoor heat and push it indoors. There is less heat outdoors as the temperature drops. The question then becomes which heat pump is efficient (electric cost per BTU of heat) in extracting the heat from the outdoors.

If you are comparing the performance of heat pumps, you need to look at how much heat they will produce at low temperatures. Most manufacturers report the heat performance at a high outdoor temperature and a low outdoor temperature. The low outdoor temperature is the key indicator of performance in my opinion. You will be surprised heat pumps which are advertised as highly efficient will have a significant drop off at low outdoor temperatures. You also have to remember the heat loss of a house increases as the outdoor temperature drops. Heat pump manufacturers will claim their heat pump will produce heat down to a low temperature, But unless the heat pump is oversized by a large amount, the heat produced will not be enough to maintain a comfortable indoor temperature. At low temperature supplemental heat is needed which is electric resistance heat in most cases.

Heat pumps operating in heating mode essentially are air conditioning / cooling the outdoors. Air conditioners, in definition of a system that cools the inside of the house but doesn't heat it, are heat pumps that cool the indoors and heat the outdoors, they're just not traditionally called heat pumps.

I am not sure what you mean by "100% efficient".

Not needing emergency heat. Most of the time in my experience it's those costly electric resistance heat strips. That's more than 100% efficient... closer to 300%, you know if you start comparing operational costs of the two. The kiss method of explaining it.

I've never seen my Bosch go into defrost, I disabled electric strip heat a year ago. Now that's efficient. (you have to understand, there's two different kinds of "efficient" -- there's the kind that saves you money, the other is just a twist on words with no benefit to run costs.)

Could you do what I did regardless of location? I don't think so. But I live where I live, you live where you live. I deal with problems in my location, not yours. Welcome to the internet.

These comments are trying to explain things simply without going to far into the weeds. We'll see where the board decides to go next...

choose the blue pill and we leave everything as it's laid out thus far.

Take the red pill and we'll start chasing rabbits down rabbit holes. Once you take the red pill, there's no turning back. LOL.

I effectively disabled the strips on my old system by locking-out the auxiliary to 25°F ambient, which rarely occurs here (did in the Feb 2021 freeze). Of course they still functioned during defrost. Most of the time I had one of the breakers for the air handler/strips turned off so one of the two strips couldn't energize. It kept up fine.

The new system is 2-stage, or effectively 3-stage heat if considering low compressor, high compressor, and auxiliary (the thermostat configuration refers to it as a 3H/2C heat pump with auxiliary). No thermostat lock-out control for the auxiliary. :-( This morn 31°F ambient, set at 69°F, running at 1st stage best as I can tell. Sometimes running for reasonably long cycles but it is cycling and holding the target temp. Noticed in one instance this morning that the blower was running at a higher speed for several minutes so presumably that was 2nd stage ... or maybe the auxiliary did energize for a bit. One of the two breakers is off.

I think that a further explanation is required here regarding damage to HP if turned ‘OFF’. The answer is a possible YES.

If your heat pump has a ‘Crankcase Heater’ and the power is disconnected from this circuit in cold weather, particularly in extreme cold weather. When power is turned ‘ON’ again, the HP should NOT be used again for about 4 to 6 hours (consult your technical installation or service manual). The reason for this is that the refrigerant contains lubricants for the compressor that might become very viscous and therefore not optimally effective to lubricate the compressor on cold turn-on. Therefore it would be better to wait until the crankcase heater has had sufficient time to properly heat the lubricants before initializing the HP otherwise there might not be an optimal oil return to the compressor to keep it from undue wear and a shortened life-cycle.

BTW: I live in an extreme cold climate where temperatures have recently been close to -40˚C/F. This is my first hand experience.

IMPO

SR

Yes, but turning it Off at the thermostat shouldn't have that effect. The OP isn't clear on what degree of off-ness is the aim.

I agree with Charles Ross' comment. The efficiency of the heat pump is measured independently of any auxiliary heating. Heat pumps are sized for their cooling load. Therefore in the southern states where summers are hot and winters are mild the heat pump is able to produce enough heat without electric heating back up.

"If your heat pump has a ‘Crankcase Heater’ and the power is disconnected from this circuit in cold weather, particularly in extreme cold weather."

The OP said turning it off, not disconnecting it. To me, that suggests a thermostat setting below where it would kick on. Do they mean or do the same thing?

Sorry I was unclear - I had no idea there were different degrees of offness! I just meant turning it off with the remote.

Does this mean if the power is off for several days when i’s below freezing that I shouldn’t turn on the heat when it’s restored until the unit has had a chance to reacclimate?

The efficiency of the heat pump is measured independently of any auxiliary heating. Heat pumps are sized for their cooling load.

auxilliary heat when electric heat strips are used is 100% efficient. For every btu you burn you get 1 btu in return. But that doesn't do anything for you when the electric bill comes.

That's not the "kind" of efficiency I was talking about now was it?

Welcome to Fantasy Island. (The Matrix if you prefer) Ha-ha.

"That's not the "kind" of efficiency I was talking about now was it?"

I still have no idea what "kind" of efficiency you were talking about, Ray. From what I gather, you've confused "efficiency" and "capacity." Here's how it went:

@mike_home: "I am not sure what you mean by "100% efficient".

@Austin Air Companie: "Not needing emergency heat."

Heat pumps--irrespective of their efficiency rating--are only able to meet the heating needs without supplemental heat when their heating capacity is greater than or equal to the balance point (the point at which the heat output is equal to the home's heating load requirements.) For conditions below the balance point, supplemental heat is needed. To be clear, that's about capacity, not efficiency.

The HVAC system designer needs to calculate the required heating and cooling loads and the ventilation requirements and design a system best suited to meet those requirements. For conditions where a heat pump is inadequate to meet the heating load and supplemental heat is needed, it could be provided by electric strip heaters or, in the case of a hybrid system, a gas furnace or the homeowner could turn it off, crank up the wood stove and wait for warmer weather.

For conditions where a heat pump is inadequate to meet the heating load and supplemental heat is needed.

Not all equipment is created equal in the heat pump realm. If you installed more than builder grade equipment Charles you'd know that.

Just spitting out buzz words like "efficiency" doesn't tell the whole story. Most people when they think efficiency they think less costly, that isn't always the case in HVAC. What I was explaining was directly related to how "most people think" -- cost of running it.

In terms of capacity, yes a traditional heat pump will lose heating capability as temps fall. But I wasn't talking of a traditional heat pump at my house now was I?

2 forms of heat? I use 1 to heat my home. 1 is less than 2. Don't make it harder than what it is Charles.

Does this mean if the power is off for several days when i’s below freezing that I shouldn’t turn on the heat when it’s restored until the unit has had a chance to reacclimate?

If you had a traditional 1 or 2 speed heat pump, then yes I would be a little hesitant to operate it for a few hours until after power is restored. Inverters are much better capable to combat this situation. I wouldn't give it much thought.

Primarily there are more controls on inverter machines that will prevent operation under dire conditions, where as a traditional heat pump will just continue to run itself into the ground.

Lamborghini vs Pinto -- the Lambo costs more for more reasons than just efficiency. ;-)

I think you've mixed up efficiency and capability again, Ray. The Lamborghini costs more than a Pinto did, even adjusting for inflation, but it's certainly not more efficient: the Pinto averaged 25 mpg. The 2021 Lamborghini Urus gets 12 mpg in the city and 17 mpg on the highway.

Charles you ever hear of tongue in cheek expression? (I meant what I said in more of an ironic way than anything else.) Clearly you do not. I said it once don't make it harder than what it is.

The inverter costs more, performs better. When refering to Lamborghini in this way I am referring to cost & performance, not gas mileage. You have to understand context. Clearly you don't Charles... and that's ok by me.

I know I am not going to pull you out of the builder grade world you reside in. That isn't my job. ;-)

Absolutely incredible!

Re: Charles Ross Homes

“Heat pumps--irrespective of their efficiency rating--are only able to meet the heating needs without supplemental heat when their heating capacity is greater than or equal to the balance point (the point at which the heat output is equal to the home's heating load requirements.) For conditions below the balance point, supplemental heat is needed. To be clear, that's about capacity, not efficiency.”

I understand what you’re saying and what you mean. Your statement is true but it’s not the whole story.

There is something missing from this discussion, that of back up auxiliary heat or supplemental heat being part of an efficiency calculation or at least a consideration of an air source heat pump. Such as type of defrost, timed (every 45min, 60min, 90min), on-demand defrost (when deemed necessary), the staging or non-staging of elements.

Defrost mode impacts efficiency. Only geothermal has no defrost cycles - ever !

This is important as the end user pays for everything - capital costs, energy, maintenance, and life-cycle replacement costs.

As always, I write this not only for this discussion today but for future readers that might come across this thread years from now.

IMPO

SR

As I said, my total oil heating fuel cost last year was $50.

Oil would have been used for just some hours of heating when outside temperature was under 30 degrees AND ANYTIME DEFROST WAS CALLED FOR.

The cost of defrosting my unit is peanuts... no matter if it is timed, on-demand, or any other scheme.

"Defrost mode impacts efficiency. Only geothermal has no defrost cycles - ever !

This is important as the end user pays for everything - capital costs, energy, maintenance, and life-cycle replacement costs.

As always, I write this not only for this discussion today but for future readers that might come across this thread years from now."

So if someone spends the extra $25K or more in one of the limited locations where a ground source system is possible and permitted, in how many years will the substantial additional cost be paid for from savings from not having to pay for defrost cycles?

My neighbor has a water heater loop on his geothermal.

As I said, my total oil heating fuel cost last year was $50.

Oil would have been used for just some hours of heating when outside temperature was under 30 degrees AND ANYTIME DEFROST WAS CALLED FOR.

The cost of defrosting my unit is peanuts... no matter if it is timed, on-demand, or any other scheme.

------------- This above is all possible, HOWEVER:

With this thought you are only thinking about the heating side of the equation. In a warmer climate... a climate that is typically better for needing HP's as well as air conditioning?

So the equation above is only looking at the costs of emergency heat because they can be separated because it's a different fuel than electric. It doesn't tell you what you are paying in electric utility costs to run the heat pump. It doesn't tell you how much the electric bill is for operating in AC mode.

The HP & AC mode: these aren't separate machines. It's all too common that people want to argue one side of the argument without considering the whole picture.

Did I only elect to put in an Inverter heat pump only to save $50, $100, $200 a year on heating costs? No. Would anyone else do that? I doubt it, unless they are listening to nonsense somewhere over the rainbow.

So for me if save $50 a year on emergency heating costs, I save $100 a month on AC use. Plus another $20-30 month on gained performance in heating mode. (inverter)

Tally all that up we're then talking in the range of $850 a year depending on utility price per KWH and a few other factors. This number is consistant for me. *Your mileage may be better or worse. So at $850 per year in savings how does it not pay you back?

Remember I know, vs what you know. I have videos that show my results comparing the former before my inverter. So the argument against the inverter is at best a cheap argument. People arguing things they clearly do not understand.

Typically what I see... an inverter AC in AC mode will cut your electric bill in half. The heating side for a warm climate is just gravy IMHO. AC mode is what I bought mine for. I would do it again, althought I would choose the Bosch 2.0 version as it's slightly more *efficient* in the right way as in what it will cost you to run it.

I service the Katy, Texas area.

Huh? lol

NIce to know I'm not the only one scratching my head on this. The OP's question is with regard to heating with a heat pump--not air conditioning with a heat pump. I don't think they intended a one-trick--HVAC-pony segue into a commercial for a Bosch inverter system.

The need for supplemental heating where a heat pump system is designed to provide both central air conditioning and heating is a function of the heating capacity of the particular heat pump vis a vis the climate zone, and the attributes of the particular home (e.g., size, insulation, air infiltration rate, glazing area, etc.)--not the efficiency rating of the heat pump. Stated otherwise, a properly sized, but low-efficiency heat pump may meet the heating demand and an undersized, high-efficiency heat pump may not. Whether the heat pump is a single-stage, a multi-stage or inverter heat pump matters not. Whether it was born in Germany or the U.S. matters not. It's about capacity--not efficiency or national origin.

In a heating climate zone, it's reasonable to expect there will be periods when supplemental heating is required for a heat pump system. In a hot-humid climate zone--like Katy, TX, (in Ray-speak, a "tropical-like" climate)-supplemental heating will rarely, if ever, be required (last year's Texas freeze being a notable exception. By the way, did you resort to burning the furniture, Ray?) The ability to do without supplemental heat is not a testimony to higher efficiency but rather a heat pump's heating capacity.

(last year's Texas freeze being a notable exception. By the way, did you resort to burning the furniture, Ray?)

The power went out, you don't run heat pumps without power. But that's like a one in 20 to 30 year event here. We can only hope ERCOT does their job here. No I didn't burn furniture, just pretended I was on a camping trip... not that difficult to figure out. Nearly everyone here was without power -- so there was no real choice in that matter. It was an experience I can tell you that much. Not many could handle Texas life, that's for sure.

Pretty boring this year compared to the rest of the nation.

PS: If you have a heat pump, you also have an air conditioner. It's the same machine. In the summer time it pumps the heat outside.

What Charles Ross said.