Cold Climate Heat Pumps

[OVERKILL]

How big of a space are you trying to heat?

3,200 square feet approximately, but it's a century home with no exterior insulation behind the double brick and some, though I'm not sure what the R value is, in the attic. We also need to do new windows, they are period correct at the moment, lol.

 

[CDX825]

Here’s a question I could not not find the answer to on the net. At what outside temperature is a 60,000 BTU per hour ( 5 ton) unit rated at. We all know about COP’s but what’s the assumption on the outside temp for the nameplate output?

Heat pumps are rated at 47 degrees for heating output.

 

[mattd]

3,200 square feet approximately, but it's a century home with no exterior insulation behind the double brick and some, though I'm not sure what the R value is, in the attic. We also need to do new windows, they are period correct at the moment, lol.

That’s a big space for 2.5 tons. Especially with poor insulation. I assume this isn’t an inverter style unit?

 

[OVERKILL]

That’s a big space for 2.5 tons. Especially with poor insulation. I assume this isn’t an inverter style unit?

Yes, it's an inverter style unit, it's a Carrier. I was somewhat limited by my panel (100A) but the setup is hybrid, so the goal wasn't to completely replace my gas furnace, just greatly reduce its use, which it seems to be doing. The unit is more than capable of keeping the house cool in the summer, so that's good.

 

[Snagglefoot]

Back to my original - Last night it was 30F here . I didn't turn the upstairs HWBB on yet. Bosch T-stat was reading 64F which was the set point on heat. It would turn on and off randomly. Downstairs HWBB T-stat set on 65F. According to my IR temperature gun I was getting 84-87F out of the registers so about a 20F rise in temperature. I'm not sure how that would perform overall at that 4F rating.

Helped to try and diagnose wife's friends heat pump setup. They were only getting about 68 degrees from vents and it was 45F outside. They had it "charged " over the summer as AC wasn't working. I don't have the equipment or certifications etc for freon or deeper stuff. They called another HVAC guy that came by after work. He checked and said Schrader valve is leaking and not sure if other. He said he'd be back Monday/Tuesday when it's warmer out to evacuate/change valve/recharge/check for other leaks and get correct pressures. He also went through the system to find previous owner had stuff wired wrong so his Electric heating coils were not working. He got that corrected so they had heat at least. So far they paid $250 which is actually really good as he was there almost 4 hours.

May I suggest you use a normal contact thermometer to check the temp. I’ll bet it’s higher.

 

[Slick3914]

Nope! The bottom line is that it is possible to make a heat pump perform well in relatively cold weather through a few mechanical "tricks". There is more to it than simply speeding up the compressor, but that's the majority of it.

But we must remember, a COP of 2.0 only means it is 2x more effective than electric resistance heat. The COP will drop to below 2, as we trend beyond the below zero point.

Sooooo, burning natural gas, at 97% efficiency is still considerably more efficient from a fuel use standpoint than a COP of 2.0. As the grid is 33% efficient.

Put another way, at a COP of 2.0, the power plant is using more energy than simply burning gas in your home.


Yes, I know it may not matter to the homeowner's bottom line as energy costs vary, but it is good to understand that the efficiency is not over unity in cold climates.

My home has a dual fuel system, gas burner takes over at less than 35F for this very reason. Heat pumps keep getting better and better so I would imagine the cross over point could be at a lower temp with a newer unit.

 

[Snagglefoot]

My home has a dual fuel system, gas burner takes over at less than 35F for this very reason. Heat pumps keep getting better and better so I would imagine the cross over point could be at a lower temp with a newer unit.

My neighbor’s new Daiken is set to 0 F, and I made it a point to go over last winter to check if it was functioning well. It was.

 

[Sequoiasoon]

May I suggest you use a normal contact thermometer to check the temp. I’ll bet it’s higher.

And what would I contact it with? I do have 2 of these Taylor Wired Thermometer versions. I use them on my boiler to check the output and return temps randomly. I guess I can move one of those next 30 degree night that I'm home and stick it up in a vent.

I'm not too concerned, overall my oil usage is down and my annual electric usage/costs are down. Totally related to the more efficient heat pump as compared to old AC only because nothing else has changed to reduce. If anything demand has gone up since my sons fiancé is living with us (showers/laundry etc)

 

[Snagglefoot]

And what would I contact it with? I do have 2 of these Taylor Wired Thermometer versions. I use them on my boiler to check the output and return temps randomly. I guess I can move one of those next 30 degree night that I'm home and stick it up in a vent.

I'm not too concerned, overall my oil usage is down and my annual electric usage/costs are down. Totally related to the more efficient heat pump as compared to old AC only because nothing else has changed to reduce. If anything demand has gone up since my sons fiancé is living with us (showers/laundry etc)

Yes, that would be better. I posted earlier that my infrared gun said something like 75 but my normal thermometer read 104. I believe it was due to my gun being focused on a shiny piece of metal. Later, you can check your steaks.

 

[wpod]

For sure! At 43 F (6 C) we consider putting on a t-shirt.

Below 60*f is close to freezing for me.

 

[Number_35]

Below 60*f is close to freezing for me.

We lived in NZ for a year, 20 years ago. The locals thought we were very hardy (or crazy) with our tolerance for the cold.

We met an older couple who had moved to NZ from Norway about 20 years before, and asked them whether they still found NZ's winters extremely mild. No, they said they'd lost their cold tolerance after about two years.

 

[fantastic]

I bought my first Heat Pump back in 2008 for my mobile home (14x70). Inside was a 15,000 watt electric furnace. Outside had the traditional looking A/C block that sat outside. It was 36k BTU A/C & 18k BTU Heat pump. Back then it was claimed that you couldn't run it below 40F but I did & the first December saved me $35 from prior year. I still remember that to this day b/c I was so excited about Heat Pump tech. I was sold on it once I heard an A/C in reverse, Heat from the cold outside air. I just let the Heat pump run & set the electric furnace out. I know this is not always possible depending on your set-up.

2017 Moved into the current house my grandparents bought in 1985. I've replaced all the windows, new roof, more insulation & installed a 12,000 btu Cooper & Hunter mini split (5 parts-7 compressor year warranty). Yes, this is a smaller unit but I'm really surprised at how well it works. It will dip down into the 20's & keep the house in the 60's. Our house is not huge though. If I can fit the inside unit in the existing space I'll get an 18k btu next time. I installed a 35k BTU Empire propane direct vent furnace as backup. I didn't use the furnace at all this fall & left the house on Nov, 17th. (I would've had to use the propane that week probably though).

35k btu empire propane heater below

 

[SubieRubyRoo]

Generally R40 used to be the standard for attics but R60 is now encouraged up here and is a standard in some locations.

When my buddy did his house a few years back, he used 2x8s on the walls, and did the walls at R47 and the attic at like R70. For 3400 square feet, and an electric micro boiler with radiant hydronic heat (house floor is all slab), his highest utility bill even in winter was $110 in the past 6 or 7 years. It’s amazing what 60 yards of concrete will do for you as a thermal mass…

 

[OVERKILL]

How big of a space are you trying to heat? Is yours a traditional heat pump or inverter communicating system?

~3,200sq-ft of century home with no exterior insulation and period-correct windows, lol.

It's an inverter unit.

 

[OVERKILL]

When my buddy did his house a few years back, he used 2x8s on the walls, and did the walls at R47 and the attic at like R70. For 3400 square feet, and an electric micro boiler with radiant hydronic heat (house floor is all slab), his highest utility bill even in winter was $110 in the past 6 or 7 years. It’s amazing what 60 yards of concrete will do for you as a thermal mass…

Yeah, I really have to get my butt in gear on new windows and improving insulation.

 

[92saturnsl2]

I have a 3 ton heat pump for my ~2000sf house, probably the cheapest thing money could buy, since I was renting the home at the time it was replaced in 2018. It's an International Comfort Products rebrand. It does just fine down to low teens, we keep our thermostat between 66 - 68 during the winter. A couple times a year when temps dip below that, it will switch over to the electric strip heat to supplement. At temps that low, even with the unit running nearly constantly (in and out of defrost cycles I might add), I'm still saving money over gas / traditional electric heat. Just because the units don't put out a lot of heat at temps that low, the efficiency value is still higher than creating heat. Remember that heat pumps just move heat energy from the outside to inside, they don't actually make heat.

My house is all electric and I've yet to see an electric bill over $250 a month in the dead of winter.

My 1500sf shop, I installed two 24K mini-split heat pumps. One is more efficient than the other, rated down to -5F. I keep them set on freeze protection (maintains temp at 46F), and crank them up to 68F when I'm working in there. They add about $30 a month if I use them heavily, but I haven't had them in use in the dead of winter yet.

 

[Snagglefoot]

Yeah, I really have to get my butt in gear on new windows and improving insulation.

We’re seeing retrofits done with closed cell foam (usually marked with a purple dye) which is R7 per inch. It’s done on small, old homes with 2 x 4 original studs that measure an actual 2x4 inches. They strip out the plaster and lath and wood shaving insulation and spray 3 inches of foam, good for R 21. The urea formaldehyde debacle in Canada still scares people but things are better now. I understand the old wood shavings were only good for R1 per inch.

 

[Sequoiasoon]

We’re seeing retrofits done with closed cell foam (usually marked with a purple dye) which is R7 per inch. It’s done on small, old homes with 2 x 4 original studs that measure an actual 2x4 inches. They strip out the plaster and lath and wood shaving insulation and spray 3 inches of foam, good for R 21. The urea formaldehyde debacle in Canada still scares people but things are better now. I understand the old wood shavings were only good for R1 per inch.

The spray foams also seal most of the gaps and cracks so that is an added factor for improvement.

 

[Finn]

I have two Mitsubishis heat pumps, one in the house and the other in garage.

No need to have the electric radiators on even in -20...25°C.

 

[Number_35]

The spray foams also seal most of the gaps and cracks so that is an added factor for improvement.

Yup, air infiltration is a real thing that is not measured by R-value.