[NA] Heat pump frost

[Let'sgoflying!]

33°F 70%RH

I noticed the outdoor unit making an odd fan-noise this morning - the coils were solid frost and not permitting any air.
The house remained warm and I did not smell the heat strips.
I ran the A/C a few minutes; frost can right off, I let it go another 15 mins for the moisture to dissipate.

An hour later, more frost and time, in sections.

Ignore?
Prepare to replace?
Some preventive intervention?

 

[Larry in TN]

I copied your post into Microsoft's AI tool. Here's it's output.


It sounds like your heat pump might be experiencing a defrost cycle issue or restricted airflow. Here are a few things to consider:

1. Defrost Cycle: Heat pumps have a defrost cycle to prevent ice buildup on the outdoor coils. If the defrost cycle isn't working properly, ice can accumulate and cause the fan to make odd noises1. You might need to check the defrost control board, temperature sensor, or reversing valve.
2. Restricted Airflow: If there's restricted airflow due to a dirty air filter or debris around the outdoor unit, the coils can freeze up. Make sure the air filter is clean and there's no debris blocking the airflow1.
3. Low Refrigerant Levels: Low refrigerant levels can also cause the coils to freeze. This is something that should be checked by a licensed HVAC technician1.
4. Moisture Dissipation: Running the A/C to defrost the coils and letting it run for a while to dissipate moisture is a good step. However, if the issue persists, it might be a sign of a more significant problem.

Given the recurring frost and noises, it might be best to contact a professional HVAC technician to diagnose and fix the issue. They can ensure that your heat pump is functioning correctly and safely.

 

[AKiss20]

Any heat pump should have some form of defrost logic to run a defrost cycle which puts the outdoor unit in cooling mode but doesn’t run the OU fan (pumps heat from the house directly into the fins). Some are just every X minutes when the temperature is less than Y degrees and some are more advanced but it should have it. If you aren’t seeing defrost cycles at these temperatures every 60-90 minutes of run time, there is likely something wrong. I would reach out to your HVAC company.

That being said, that level of frost is normal to build up in between defrost cycles. So if it is running defrost cycles normally I wouldn’t be concerned. My heat pump gets frostier than that and still works fine (granted it is a cold weather heat pump that theoretically gives full output down to -5F) so if you’re getting actually zero heat at that level of frost (as in 0-2F rise across the indoor coil, not like 15F-30F which is a typical temp rise across a heat pump coil in the winter) then something else is likely wrong. Again reach out to your HVAC company.

 

[Capt. Geoffrey Thorpe]

They frost up regularly, and the defrost cycle sounds "odd".

 

[sourdough44]

A little ‘old school’ here. I like it in the mid 70’s, or higher.

 

[Shepherd]

-9° here this AM. My pellet stove is running full tilt boogie and my neighbors are
sitting in my living room because their heat pump crapped out.
This is the coldest day we've had since they installed it last summer.
I hope this isn't normal. I have no heat pump knowledge at all.

 

[Larry in TN]

-9° here this AM. My pellet stove is running full tilt boogie and my neighbors are
sitting in my living room because their heat pump crapped out.
This is the coldest day we've had since they installed it last summer.
I hope this isn't normal. I have no heat pump knowledge at all.

Heat pumps weren't normal in NY until recently, were they? I know now they have heat pumps designed for very cold conditions.

A quick search finds that conventional heat pump's efficiency starts dropping rapidly below 40°. Cold-climate heat pumps extend that down to around -4°. -9° is going to be a challenge for all of them.

Is their heat pump failed, or just overwhelmed with the low temps?

I have gas heat downstairs and a conventional heat pump upstairs. The heat pump is running the AUX heat almost continuously at our temps this week dipping in the teens and single digits. It won't be a fun electric bill next month. Luckily, this only happens for brief stretches each winter in Tennessee.

 

[Bill]

The aux heat ran for about an hour last night, otherwise the heat pumps seemed to do the job. Low was 9*F. Still, power bill will be large this month.

 

[MauleSkinner]

I have no heat pump knowledge at all.

Heat pumps suck when it’s cold.

 

[Larry in TN]

The aux heat ran for about an hour last night, otherwise the heat pumps seemed to do the job. Low was 9*F. Still, power bill will be large this month.

That's pretty good. Do you know if it's a conventional or cold-weather heat pump?

 

[Bill]

That's pretty good. Do you know if it's a conventional or cold-weather heat pump?

Two year old Trane XV18 variable speed, don’t know of it’s specifically a cold weather model.

 

[Bill]

Two year old Trane XV18 variable speed, don’t know of it’s specifically a cold weather model.

It’s 28 outside now and it’s running at 43% to maintain 68 inside.

 

[Shepherd]

Heat pumps weren't normal in NY until recently, were they? I know now they have heat pumps designed for very cold conditions.

A quick search finds that conventional heat pump's efficiency starts dropping rapidly below 40°. Cold-climate heat pumps extend that down to around -4°. -9° is going to be a challenge for all of them.

Is their heat pump failed, or just overwhelmed with the low temps?

I have gas heat downstairs and a conventional heat pump upstairs. The heat pump is running the AUX heat almost continuously at our temps this week dipping in the teens and single digits. It won't be a fun electric bill next month. Luckily, this only happens for brief stretches each winter in Tennessee.

I think it's just overwhelmed by the cold.
Also, he was too cheap to upgrade their power panel when they installed the heat pump, so it popped the main circuit breaker when it started drawing more electricity.
Apparently it's a heat pump until it runs out of heat then becomes an electric heat system? The house was originally oil fire baseboard hot water.
He's over there with the people who installed it. She and the kids are here staying warm, and she is saying not nice things about the system, the people who installed it and her husband who decided to go "more green".

I'm just trying not to laugh out loud while my wife is trying to calm things down and giving me dirty looks because I keep snickering.
But their 2 kids and I are having great fun alternating between flying the indoor battle copters and having tank battle with the RC tanks.

Snow days are great.

 

[Bill]

I think it's just overwhelmed by the cold.
Also, he was too cheap to upgrade their power panel when they installed the heat pump, so it popped the main circuit breaker when it started drawing more electricity.
Apparently it's a heat pump until it runs out of heat then becomes an electric heat system?

Yes, when the heat pump alone is no longer sufficient, the system kicks in electric resistive heat strips. Those same heat strips normally also kick in when your heat pump goes into defrost mode as well.

It’s a good idea to have sufficient electrical service to operate the system.

 

[AKiss20]

Heat pumps suck when it’s cold.

Modern cold weather heat pumps can put out full heat well into the single digits F and some even below 0F.

My heat pump can produce the same heat output at -10F as it can at 45F. We run it down to 20F because at that point it’s substantially more economical to use our NG furnace.

 

[MauleSkinner]

Modern cold weather heat pumps can put out full heat well into the single digits F and some even below 0F.

My heat pump can produce the same heat output at -10F as it can at 45F. We run it down to 20F because at that point it’s substantially more economical to use our NG furnace.

I guess 8 years old isn’t “modern”, or else I don’t have a “cold weather” one.

 

[AKiss20]

I guess 8 years old isn’t “modern”, or else I don’t have a “cold weather” one.

Yes 8 years old is quite old in the HP world, things have improved rapidly. They still sell older models that struggle in colder temps but the norm is moving to these cold weather HPs.

 

[Larry in TN]

Apparently it's a heat pump until it runs out of heat then becomes an electric heat system? The house was originally oil fire baseboard hot water.

That's normal for a heat pump. It has electric resistance heating elements to supplement heating when the heat pump is unable to maintain the set temperature. It's called AUX heat. It is very inefficient, and will really run up your bill, but it provides heat when you need it. Those systems will also have an EMERGENCY heat mode that turns off the heat pump portion and only runs the AUX heat.

I think the cold-weather heat pumps cost more than the conventional ones so they aren't installed in climates that rarely need the extra capability unless the homeowner asks for it.

 

[Bob Noel]

bit of triva: not all heat pumps have the ability to supplement the output with electric heat.

 

[chartbundle]

bit of triva: not all heat pumps have the ability to supplement the output with electric heat.

This is why I didn't remove my electric wall heaters when I put in the mini-split. Although it's not been needed because it was too cold just when it fails one of the 37 electronic components and needs service.

 

[tspear]

I have gas heat downstairs and a conventional heat pump upstairs. The heat pump is running the AUX heat almost continuously at our temps this week dipping in the teens and single digits. It won't be a fun electric bill next month. Luckily, this only happens for brief stretches each winter in Tennessee.

Heat rises, turn up the temp downstairs, turn down the temp upstairs. That will help the bill....

Tim