Newer Heat pump question

[Richard Cranium]

We had a new heat pump put in and was told that the new ones were so much more efficient then the old one. My question is at what temp am I better off and just let the Eletric furnace do the heating? Thank you in advance. Rich

 

[larry4406]

Usually the installer sets the temp per the MFR as to when the resistance elements kick in.

 

[PoorUB]

We had a new heat pump put in and was told that the new ones were so much more efficient then the old one. My question is at what temp am I better off and just let the Eletric furnace do the heating? Thank you in advance. Rich

We would need more information to give you an answer, make and model to start. Some heat pumps stop being efficient to heat around 10F to 20F. Others will run to well below zero.

I would say with typically is out there about 20F it starts getting close to change over, but again, not knowing specifics it is just a guess.

 

[pattenp]

My strips kick in when the HP doesn't keep up or make headway. There is no set outside temp. Depends on if house is losing heat quicker than the HP can produce it.

 

[rebelranger]

Read the tech data. Most heat pumps lose efficiency at 47f and bottom out at 17f. Higher end, hyper heat, models heat to -22.

I have cheap mini split heat pumps that barely give off heat at 17f and I have a top of line 4ton heat pump that works fine at 0.

Short story read the tech data on your device to see its heat to temperature graph.

 

[mike93lx]

RTFM.

Mine is set to cutover at 20F

 

[Richard Cranium]

Thank you very much, it is 18 deg. and it seems like it is working very hard.

 

[mepstein]

I have propane backup and I set it to turn on at 25. Mostly because the temp of the heat pump is still warm but feels cool when the air hits you. The app for my nest thermostat lets you adjust it in seconds from your phone.

 

[HoosierMark]

I have a bunch of them in my apartments and just let the factory settings work. If they cannot pull enough heat from the outside air, they automatically kick on the electric strips. My tenants do not need to do anything. Only issue I usually hear about is the air out of the registers is not hot. Then I explain that they move a large volume of air at a lower temp while furnaces move less air at a higher temp.

 

[Magnum440d100]

I had an all new American standard put in, in 2019.

When it got down into the negatives last night, it ran absolutely non stop. I thought it was going to burn out.

Now that it’s above 0 (12°F) it’s a bit more comfortable in here. I think the strips came on a couple times during the night, and kept it at 70°F in here, but now it feels like a warmer 70°F if that makes sense lol

 

[mike93lx]

I had an all new American standard put in, in 2019.

When it got down into the negatives last night, it ran absolutely non stop. I thought it was going to burn out.

Now that it’s above 0 (12°F) it’s a bit more comfortable in here. I think the strips came on a couple times during the night, and kept it at 70°F in here, but now it feels like a warmer 70°F if that makes sense lol

If it can keep the temp you want, running non stop is perfect on the coldest day. Means it's sized right

 

[Wiz02]

@rebelranger, @mike93lx I have a similar setup, heat pump with propane backup. HVAC installer has the thermostat set to factory default which is 40 deg F. What am I looking for when I RTFM, is it an efficiency curve, is there some magic HVAC acronym that I am looking for?

 

[mike93lx]

@rebelranger, @mike93lx I have a similar setup, heat pump with propane backup. HVAC installer has the thermostat set to factory default which is 40 deg F. What am I looking for when I RTFM, is it an efficiency curve, is there some magic HVAC acronym that I am looking for?

Efficiency curve. To get really accurate you would need to calculate the cost per btu output at each temp with each fuel and find the balance point. I just have mine set at where efficiency starts to drop off as I wanted to try and prioritize the heat pump

 

[Wiz02]

Efficiency curve. To get really accurate you would need to calculate the cost per btu output at each temp with each fuel and find the balance point. I just have mine set at where efficiency starts to drop off as I wanted to try and prioritize the heat pump

Thanks, I will start with where the efficiency drops off and see about doing the cost calculations, but I am not touching the hvac until the cold snap ends.

Do I need to worry about defrost settings if I can set the balance point below freezing?

 

[CombatNinja]

They all drop off below freezing, it just depends to what extent. I live in southern N. Carolina and it is freaking freezing here. My mid-priced 16 SEER unit doesn't stand a ghost of a chance in this weather. It has said "AUX HEAT" just about every time I've walked past it today. Cranking the propane fireplace tonight to help it out. This weather is ridiculous.

 

[Wiz02]

Mid Atlantic Temps can't compare to areas that are really cold, but we haven't seen 9 degrees F in a very long time in Southeastern PA. My propane furnace isn't quite running flat out, and it isn't struggling to maintain the SWBO required temp of 72, but it's running 45 minutes or more out of an hour at that temperature. I'm going to need another job to pay the propane bill!

 

[mike93lx]

Do I need to worry about defrost settings if I can set the balance point below freezing?

I'm no expert, but my units are running fine at a 20 degree setpoint so far this season.

 

[walta]

They all drop off below freezing, it just depends to what extent. I live in southern N. Carolina and it is freaking freezing here. My mid-priced 16 SEER unit doesn't stand a ghost of a chance in this weather. It has said "AUX HEAT" just about every time I've walked past it today. Cranking the propane fireplace tonight to help it out. This weather is ridiculous.

Ninja your statement is wrong about my heat pump and many others!

I set my 17 SEER heat pump to lock out the auxiliary heat when the outdoor temp is above +5°F. I have a posted a link showing my HP has a COP over 2 at -5°F

The way I see it my 4 ton unit produces 34200 BTUs at +5°F that is 70%.

https://ashp.neep.org/#!/product/56474/7/25000///0



Walta

 

[firebirdparts]

Efficiency curve. To get really accurate you would need to calculate the cost per btu output at each temp with each fuel and find the balance point. I just have mine set at where efficiency starts to drop off as I wanted to try and prioritize the heat pump

This is the real answer. The other answers are just Gibberish. When the COP gets to one, it's equally cheap to go to emergency heat. You're not getting anywhere near that at a reasonable temperature. Back in the 8 SEER days, the rule of thumb for an outside temperature switch was 20F, but those switches weren't intended to cut the compressor off. They weren't saying COP was 1 at that temperature. But the main issue is those days were 40 years ago.

 

[walta]

We had a new heat pump put in and was told that the new ones were so much more efficient then the old one. My question is at what temp am I better off and just let the Eletric furnace do the heating? Thank you in advance. Rich

Richard, try entering the make and model of your heat pump in this data base and see if it has been tested. My heat pump has a COP of 2.08 at -5°. What that means is my heat pump will produce BTUs for less than half the cost of the back up electric heat so it is never cheaper to switch over.

Understand as the temperature drops heat pumps do lose capacity in that they are not able to produce as many BTUs at the same time as it gets colder every house requires more BTUs. Every house has it's balance point a outdoor temp at which this house requires the same number of BTUs as its system can produce at that temp to keep that indoor set point. The only real way to find that balance is to lock out the back up heat and wait for it to get so cold the system can’t maintain the set indoor temp. For my house that is below +5°F yours will be different.

The way I see it the important setting is the lock out for the electric heat to keep it off when the outdoor temp is above your balance point temp and not the setting you are asking about outdoor temp at which the heat pump gets locked out below.

ASHP

ashp.neep.org

Walta

 

[buzzworth]

My office/garage building has an older air/air heat pump and it's holding 55* while the outside is 9*, but just barely. When we went any lower it would give it a shot of strips.
In the house we run geothermal and has been cycling normally (well, a bit more than usual due to the frigidness). But I have found many air infiltrations in the envelope of the SIPS panels that enclose this timber frame structure. I've been trying to seal them where I can get a foam nozzle.
I hope everyone is bearing with this cold. It's good to see you west coasters getting rain and snow in the mountains, keep it up.