# Opinions on heat pump backup



## That's Right (Mar 25, 2014)

In need of a new heat pump for house. 2800sqft 2 story house built in 96 in central PA.  HP is 10years old and got a workout this winter. Question is to replace with electric resistance backup or propane?  Have resistance now and electric bills were $500mo during cold spells. Usually during those months it is $300-350. 

Option to go with propane as backup,  but would have to either rent/buy tank.  Would have to go with 2 100lb tanks that I would probably buy. Burying a large one would probably be too expensive. 

Would have HP set to work down to 25 or so. 

Both quoted about the same price through buddy/hookup. 

The p61 heats the basement. 

Thanks for the opinions


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## velvetfoot (Mar 25, 2014)

You could plug your fuel costs into this spreadsheet:  www.eia.gov/neic/experts/heatcalc.xls

Around here, last I checked, propane is more expensive than oil and resistance electric is just a little less than propane.  Maybe go whole hog on the most efficient heat pump you can get so the backup doesn't come on that much, and get a pellet stove, or something, upstairs.


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## rkusek (Mar 26, 2014)

That's Right said:


> In need of a new heat pump for house. 2800sqft 2 story house built in 96 in central PA.  HP is 10years old and got a workout this winter. Question is to replace with electric resistance backup or propane?  Have resistance now and electric bills were $500mo during cold spells. Usually during those months it is $300-350.
> 
> Option to go with propane as backup,  but would have to either rent/buy tank.  Would have to go with 2 100lb tanks that I would probably buy. Burying a large one would probably be too expensive.
> 
> ...


What's your electric rate in winter?  I would think twice about  a propane backup.  Propane prices change so much and the propane backup changes completely to gas at the cut off temp.  Electric backup will work together with the HP to attempt to maintain the home temp.  When I'm not running my wood boiler, the HP is still operating down at zero with shots of electric resistance occasionally.  Maybe your attic insulation has settled making it less effective.  Check your end joist bays on a very cold day.  My 2009 home just has batts there and they were wet and frosty on our coldest days this winter.  Going to add pink foam behind the batts sealed with great stuff or get a spray foam kit this summer.  My 5 ton HP has a 5kw and a 10kw strip I believe.  It would be better if they were staged and the blower was variable speed but my system is pretty basic.  I think propane backup which my dad has would actually cost you more every month.


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## velvetfoot (Mar 26, 2014)

rkusek, still, it gets pretty cold where you live,  and your new home got built with a heat pump, which is interesting to me.


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## flyingcow (Mar 26, 2014)

Very new to me, I;ve been running a Mitsu 18k btu air sourced heat pump most of the winter. Seems to work well, haven't seen $50 or $60 increase in electric, BUT still running wood boiler for a small area of radiant floor in my kitchen, upstairs zone and DHW. When it gets below zero, it will still throw pretty good heat, but I shut it off and heat with the wood boiler. The BB does a better job on those sub zero nights keeping perimeter of house warm.


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## potentialburner (Mar 29, 2014)

I would second velvetfoot's recommendation to work the eia spreadsheet.  I have a HP with propane backup and as mentioned it turns into pure propane heat at the cutoff temp.  To put that in real world terms I paid $850 for one month worth of propane during the polar vortex....and I had a discount contract that I signed in the summer,  so my propane was $3/gal while others in the area were paying $5. 

Anyway take the spreadsheet and play with it using your local kWh price to see at what point propane becomes competitive with a HP, or any other fuel for that matter. I did it for my area and the results were surprising.  I blogged it here, table near the end shows what propane has to be to be competitive with various fuels:  

http://unjustifiedprecision.blogspot.com/2014/03/propane-heat-is-for-suckers-and-yes.html

Propane backup heat was clearly a mistake.  But at the time, with much cheaper propane, it made sense.


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## flyingcow (Mar 29, 2014)

potentialburner said:


> I would second velvetfoot's recommendation to work the eia spreadsheet.  I have a HP with propane backup and as mentioned it turns into pure propane heat at the cutoff temp.  To put that in real world terms I paid $850 for one month worth of propane during the polar vortex....and I had a discount contract that I signed in the summer,  so my propane was $3/gal while others in the area were paying $5.
> 
> Anyway take the spreadsheet and play with it using your local kWh price to see at what point propane becomes competitive with a HP, or any other fuel for that matter. I did it for my area and the results were surprising.  I blogged it here, table near the end shows what propane has to be to be competitive with various fuels:
> 
> ...



Just curious, you're in NC? Why do you need a back up for a HP? Just thinking and learning.


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## chken (Mar 29, 2014)

I've been using that Heatcalc spreadsheet recently, so I pulled it up. Adjusting for an HSPF in Eastern PA, of 7.7, and using 15 cent electric and $209 pellets and $3.60 heating oil, and modern efficiencies, I get the following:
$14.30 for a million BTUs using $209/ton pellets
$30 for a million BTUs using $3.60 oil at 86% boiler efficiency
$44 for a million BTUs using electric resistance at 100% efficiency
$19.50 for a million BTUs using an air-source HP using a HSPF of 7.7 for eastern PA.

For propane to match the HP, it'd have to cost about $1.4 a gallon at 78% efficiency.

What surprised me is that for your area, a HP is not that far off using pellets, okay, 30% more ,but that's a lot close than oil or electric resistance.


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## brant2000 (Mar 29, 2014)

Maybe it's just my unit, but I'm very skeptical about the HSPF vs. "real world" efficiencies.  I only went a few months with our newly installed HP until I decided we needed to burn wood instead.  Our first cold month had an electric bill of more than 6,000 kWh .  Although it almost never runs any more, I have nightmares of listening to the thing kicking into defrost mode every 20 minutes or so.


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## chken (Mar 29, 2014)

brant2000 said:


> Maybe it's just my unit, but I'm very skeptical about the HSPF vs. "real world" efficiencies.  I only went a few months with our newly installed HP until I decided we needed to burn wood instead.  Our first cold month had an electric bill of more than 6,000 kWh .  Although it almost never runs any more, I have nightmares of listening to the thing kicking into defrost mode every 20 minutes or so.


Holy cow! 6000 kWh? That sounds more like what I would have expected for electric resistance heat.


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## _CY_ (Mar 29, 2014)

IMHO the most efficient combo is .. inverter driven ductless mini split combined with a high efficiency Cat wood stove.
ductless mini splits have been used successfully in Denver Colo winter conditions.

main heat would be provided by Buck 91 cat ..  ductless mini split would take care of fill-in heat during winter and cooling in summer. a duct less mini split is really an inverter driven heat pump .. inverter allows compressor to run at variable speeds for Maxim efficiency.


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## flyingcow (Mar 29, 2014)

brant2000 said:


> Maybe it's just my unit, but I'm very skeptical about the HSPF vs. "real world" efficiencies.  I only went a few months with our newly installed HP until I decided we needed to burn wood instead.  Our first cold month had an electric bill of more than 6,000 kWh .  Although it almost never runs any more, I have nightmares of listening to the thing kicking into defrost mode every 20 minutes or so.




Doesn't make sense.


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## flyingcow (Mar 29, 2014)

_CY_ said:


> IMHO the most efficient combo is .. inverter driven ductless mini split combined with a high efficiency Cat wood stove.
> ductless mini splits have been used successfully in Denver Colo winter conditions.
> 
> main heat would be provided by Buck 91 cat ..  ductless mini split would take care of fill-in heat during winter and cooling in summer. a duct less mini split is really an inverter driven heat pump .. inverter allows compressor to run at variable speeds for Maxim efficiency.




This basically is my thought. If I ever rebuild a new house, R-40 walls and R-60 ceilings. Quite possibly a HP with a central wood stove. The main area will be an open format, wood stove for them cold nights.


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## moey (Mar 29, 2014)

I could be wrong on this but you may want to ask your contractor about it hopefully they can give you a exact answer. 

With electric backup the heat pump will still be running when the electric backup is engaged. For instance if its 20 F outside and your heat pump is only putting out 60% of its rating its still doing so cheaper then a propane only system. The heat pump will not run in conjunction with a propane furnace. It will have a temperature at which it shuts off at and the propane system takes over. The propane system will not supplement the heat pump. 

Doing a fuel cost comparison will not give you a accurate representation of operational costs because it does not include the fact that using a electric backup still allows the heat pump to run albeit even if the COP is only 2x.


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## potentialburner (Mar 29, 2014)

flyingcow said:


> Just curious, you're in NC? Why do you need a back up for a HP? Just thinking and learning.



NC has a true four season climate, we have multiple days with lows in the 20s and even the occasional teen. 30s are pretty typical otherwise in winter.  That's too cold for a heat pump. 

Most heat pumps here have electric strip heater backup. But gas packs are also popular.  They are more economical than electric strip heat backup when you have natural gas. Before propane ran up in price it was about equivalent.  

But another advantage of a gas pack is that you can run the gas furnace on generator power and still have juice left over for the fridge, lights, etc since all you have to power to get heat is the blower motor.  That was important to me because I'm in a rural area where ice storm and hurricane caused power outages can drag on for a long time.


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## potentialburner (Mar 29, 2014)

moey said:


> Doing a fuel cost comparison will not give you a accurate representation of operational costs because it does not include the fact that using a electric backup still allows the heat pump to run albeit even if the COP is only 2x.



The EIA heatcalc spreadsheet includes a section to adjust your heat pump's HSPF based on location.  The colder your local climate, the lower it adjusts. I assumed that accounted for the need to run the strip heater backup.  

Now a gas pack doesn't calculate in that spreadsheet very easily I agree.  However comparing propane furnace cost to electric baseboard heat cost probably gives a rough approximation of the cost comparison for emergency mode.


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## rkusek (Mar 30, 2014)

chken said:


> I've been using that Heatcalc spreadsheet recently, so I pulled it up. Adjusting for an HSPF in Eastern PA, of 7.7, and using 15 cent electric and $209 pellets and $3.60 heating oil, and modern efficiencies, I get the following:
> $14.30 for a million BTUs using $209/ton pellets
> $30 for a million BTUs using $3.60 oil at 86% boiler efficiency
> $44 for a million BTUs using electric resistance at 100% efficiency
> ...


15 cent electricity is about double our winter rates which usually half the summer rates once you exceed a minimum threshold.


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## jebatty (Mar 30, 2014)

> NC has a true four season climate, we have multiple days with lows in the 20s and even the occasional teen. 30s are pretty typical otherwise in winter. That's too cold for a heat pump.


Agreed, with true four season climate it's too cold for a HP: multiple days with lows in the -20'sF and even the occasional -40'sF. +0F pretty typical. I think MN gets all the cold produced by HP's operating in winter in the rest of the US. Oops, it was that cold before HP's were invented.


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## flyingcow (Mar 30, 2014)

_*NC has a true four season climate, we have multiple days with lows in the 20s and even the occasional teen. 30s are pretty typical otherwise in winter. That's too cold for a heat pump. *_

I'm new to the HP's, but I've been using my HP most of the winter. 20's and 30's it  works very well. I haven't put a watt hour meter on it, but at 17f outside it suppose to use 2600 watts in the heating mode.


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## flyingcow (Mar 30, 2014)

Now i think for a minute, you must have central air in your house. The unit i have is a wall unit. I think there is talk of designing a central unit to work efficiently in cold weather.


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## _CY_ (Mar 30, 2014)

potentialburner said:


> NC has a true four season climate, we have multiple days with lows in the 20s and even the occasional teen. 30s are pretty typical otherwise in winter.  That's too cold for a heat pump.
> 
> Most heat pumps here have electric strip heater backup. But gas packs are also popular.  They are more economical than electric strip heat backup when you have natural gas. Before propane ran up in price it was about equivalent.
> 
> But another advantage of a gas pack is that you can run the gas furnace on generator power and still have juice left over for the fridge, lights, etc since all you have to power to get heat is the blower motor.  That was important to me because I'm in a rural area where ice storm and hurricane caused power outages can drag on for a long time.



that's no longer true for inverter driven ductless mini splits ... some  *Operates down to -15°F outdoor temperatures* with 27 seer efficiencies. 

technologies marches on .. that's why I stated early that IMHO the most efficient setup is with a ductless mini split and Cat stove like Buck 91 combo. 
Buck 91 (substantially less $$) or Blaze King model King would supply main heat with ductless mini split doing fill in duties. 

again a ductless mini split is really an inverter driven heat pump with ability to run compressor at veritable speeds.


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## potentialburner (Mar 30, 2014)

_CY_ said:


> that's no longer true for inverter driven ductless mini splits ... some  *Operates down to -15°F outdoor temperatures* with 27 seer efficiencies.
> 
> technologies marches on .. that's why I stated early that IMHO the most efficient setup is with a ductless mini split and Cat stove like Buck 91 combo.
> Buck 91 (substantially less $$) or Blaze King model King would supply main heat with ductless mini split doing fill in duties.
> ...



I've been intrigued with ductless mini splits before because of my house design... one large open space but with a separate master suite wing.  I've thought about a ductless mini split for the master suite wing as a cheaper alternative to a dual zone central system,   but haven't pulled the trigger because my current single zone central heat pump system with propane backup is still working well enough, though more expensive now that propane has gone up.  Also as I mentioned before I think it's important to keep propane heat capability for those long power outages.  

But I like to think ahead so I can make a good decision when replacement time comes (my system is coming up on 15 years old). 

Would a ductless mini split be suitable for bedroom use? What kind of power requirements do they have (i.e.,can one be run on standard portable generator with leftover juice for the fridge and lights?)  Also I'm wondering about noise as the location would be right over the head of the bed in my application.   Finally,  I read online manuals for some and they seem a little more maintenance intensive than my central system (need to clean the filters pretty often as opposed to simply replace with standard ones from the home improvement store).  

It's interesting that the discussion on heat pumps has been more informative here than at hvactalk.com.  Keep the info coming!


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## flyingcow (Mar 30, 2014)

I do not have mini splits. I have a mitsu 18btu  unit(downstairs) and another mitsu 12k(up). Dont know the model numbers. But the new inverter style I believe.  Only run the down stairs in the winter. I think they're 20 amp draw ( 18k) and 15  amp(12k). Not big energy draw? 

They are able to run with an outside temp of 15 below. Usually gets that cold and I run my base board heating. Not sure if I posted before but at 17f it pulls 2600 watts to run. Pretty impressive I think.


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## brant2000 (Mar 30, 2014)

flyingcow said:


> I do not have mini splits. I have a mitsu 18btu  unit(downstairs) and another mitsu 12k(up).



I would think those are considered mini splits.  I think any units that typically have wall mounted or cassette fan units are considered mini splits.  I believe they may go up to as large as 24kbtu.  A "regular" split HP unit is the type that resembles a standard central AC unit.  Mine is a 4 ton unit with a total of 30 kw of strip heaters for backup/defrost.  The electric meter really spins when those things heat up.


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## flyingcow (Mar 30, 2014)

Mini's have two heads and one unit outside. At least that's what iv been told


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## brant2000 (Mar 30, 2014)

flyingcow said:


> Mini's have two heads and one unit outside. At least that's what iv been told



I believe those are mitsubishi's "city multi" units.  There may be others that use a similar arrangement, but these were the original.


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## That's Right (Mar 30, 2014)

Well I went with what I had as far as backup..electric coil. Now I've got a new 4ton 15 seer hp. I can't believe the difference in air temperature. The air is actually hot compared to the old unit.  
   Thanks for all of the help. 
   By the way it is snowing blowing like crazy here. Had the perfect storm/situation happen. B-day party for my 1yoa baby girl. Electricity goes out. P61 in the basement started to leak alittle smoke. Fired up generator and newly wired box. Everything worked like a champ. That's a non pure sine wave generator by the way. 

Again thanks for the help/replies. This Site is awesome


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## brant2000 (Mar 31, 2014)

Glad everything worked out and that your happy with the new HP.  Happy birthday to your daughter!


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## maple1 (Mar 31, 2014)

flyingcow said:


> Mini's have two heads and one unit outside. At least that's what iv been told


 
I'm quite sure that one head in & one unit out is also a mini-split.


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## heaterman (Apr 2, 2014)

flyingcow said:


> Mini's have two heads and one unit outside. At least that's what iv been told



You can get inverter style mini's with anywhere from a single to 3 or maybe 4 indoor units.


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## _CY_ (Apr 5, 2014)

difference between a ductless mini-split is lack of ducting ... each room/area has it's own refrigeration lines which goes to a self contained register with blower. outside main condenser are all different sizes to support larger number of circuits. each room/area has it's own circuit.

410A outside DC compressor is inverter driven at variable speeds depending on loads. inside registers are AC driven .. 27 seer is not uncommon. sensor driven compressor fan and other features bumps efficiency. one drawback is not that many refrigeration techs are up on service/installation for ductless mini-splits. they really are different ..


vs 13 seer for lowest rated HP .. up to 24 seer for max efficient conventional compressors with variable inside fan with solenoid operated liquid line controls, etc.

it needs to be pointed out again ... when burning a high efficient wood stove like Buck 91 Cat 24x7 ... your HP/natural gas heater only should run a few times a day.  doesn't what type backup heating system you've got. it's only when relying on HP or what ever as primary heat source .. operating costs becomes a factor.


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## DBoon (Apr 5, 2014)

brant2000 said:


> Maybe it's just my unit, but I'm very skeptical about the HSPF vs. "real world" efficiencies.



Yes, it is just your unit, and I was very skeptical as well before I read all of the glowing reviews about the mini-split performance in cold weather.  But they deliver.  When it was 0 degrees F outside this winter, the air coming out of my mini-split indoor cassette was very warm. 

Having grown-up in the "bogus" era of conventional ducted heat pumps, I was very skeptical of mini-split claims.  To me, heat pumps were inefficient ways to  blow ~75 degree heat around the house and watch the electric resistance heat run half the time (it seemed) anyways,.  I could also never get the wife trained to not turn the temperature up quickly when she was cold, so the electric resistance heat was running half the time anyways.  Mini-splits just pump out heat even when it is very cold, and never turn on electric resistance heat.  

Conventional ~12 SEER heat pumps are no comparison to a good mini-split.


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## potentialburner (Apr 6, 2014)

DBoon said:


> Having grown-up in the "bogus" era of conventional ducted heat pumps, I was very skeptical of mini-split claims.  To me, heat pumps were inefficient ways to  blow ~75 degree heat around the house



Even the older "colder" heat pumps didn't blow air that cool. It was low 90s but felt cool because it was below body temperature.  Of course that fact didn't make them comfortable. 

I have one that's getting older (1999 install) and the air it blows is comfortably warm. It was top of the line then, probably at the lower end of performance by today's standards.



> Conventional ~12 SEER heat pumps are no comparison to a good mini-split.



I thought SEER was a measure of cooling, not heating, efficiency.


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## potentialburner (Apr 6, 2014)

BTW how much noise do mini splits make?  Would I be annoyed having one right over my bed?


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## flyingcow (Apr 7, 2014)

potentialburner said:


> BTW how much noise do mini splits make?  Would I be annoyed having one right over my bed?



I don't think they noisy at all. The fan is very quiet. If they've been shut off, a bit noisy upon start up trying to cool or heat room to temp. But thats just until it gets close to temp, it will ramp down the closer it gets to temp.


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## peakbagger (Apr 7, 2014)

My Mitsu mini split has three speeds. It is quite quiet on low but is noticeable when on medium. On high its noisy. Mine is mounted very close to where I sit to watch TV so it location is also an issue but I needed to put it there to get the outside unit in the best spot (Out of the prevailing winds and on a sunny wall) In normal operation running it on low is fine. If the unit has been set back and I need to heat the area up, medium is needed for an hour or two. I heat the second floor of my house with the unit on the first floor when possible and in cold condition, I need to run the fan on high. One thing to be aware of is the amount of heat the unit puts out drops as its gets colder while the amount of heat you need goes up. The unit still puts out heat at subzero temps but the btu/hr and the temp also drops. I found this winter that in cold temps, the unit really doesn't deal well with setting back the temp, just set it at one setting and leave it.

In cold damp or snowy conditions, they are somewhat noticeable when going through a defrost cycle. Its not that it loud as much as it sounds like someone is messing with the controls as it cycled through the defrost cycle. If its clear out, it doesnt happen often but in cold snowy conditions it may cycle every hour.


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## brant2000 (Apr 7, 2014)

DBoon said:


> Yes, it is just your unit, and I was very skeptical as well before I read all of the glowing reviews about the mini-split performance in cold weather.  But they deliver.


I also have heard great things about minisplits.  My comment was in regard to large, ducted split systems like mine.  Just like you mention in your post, mine blows slightly warmed air and runs constantly when it's cold out.  Aside from the expensive electric bill, the constant noise of my blower running 24x7 drove me nuts.


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## flyingcow (Apr 7, 2014)

_*In cold damp or snowy conditions, they are somewhat noticeable when going through a defrost cycle. Its not that it loud as much as it sounds like someone is messing with the controls as it cycled through the defrost cycle. If its clear out, it doesnt happen often but in cold snowy conditions it may cycle every hour.*_

Thanks for reminding me peakbagger. I should have mentioned this also.


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## heaterman (Apr 7, 2014)

peakbagger said:


> My Mitsu mini split has three speeds. It is quite quiet on low but is noticeable when on medium. On high its noisy. Mine is mounted very close to where I sit to watch TV so it location is also an issue but I needed to put it there to get the outside unit in the best spot (Out of the prevailing winds and on a sunny wall) In normal operation running it on low is fine. If the unit has been set back and I need to heat the area up, medium is needed for an hour or two. I heat the second floor of my house with the unit on the first floor when possible and in cold condition, I need to run the fan on high. One thing to be aware of is the amount of heat the unit puts out drops as its gets colder while the amount of heat you need goes up. The unit still puts out heat at subzero temps but the btu/hr and the temp also drops. I found this winter that in cold temps, the unit really doesn't deal well with setting back the temp, just set it at one setting and leave it.
> 
> In cold damp or snowy conditions, they are somewhat noticeable when going through a defrost cycle. Its not that it loud as much as it sounds like someone is messing with the controls as it cycled through the defrost cycle. If its clear out, it doesnt happen often but in cold snowy conditions it may cycle every hour.



How old is your Mits and is it an inverter type unit?


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## peakbagger (Apr 8, 2014)

My mitsu is a hyper heat inverter unit bought last year. I have strictly AC Mitsu seven years old in my office. The blower noise is just about the same. Barely noticeable at low, and noisy on high. I am considering replacing the office unit with new heat pump (another NH rebate).


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