It's been cold here lately and when it gets real cold are you seeing this from your heat pump?
Does it look like an ice cube?
A heat pump is essentially an air conditioner that can work backwards!
In winter months many heat pumps will have to put themselves through what is called a "defrost cycle."
During the heating season, a heat pump will compress heat from outside and transfer it indoors.
When the air outside is very cold, it will freeze on the heat exchanger when the fan is blowing air over it. The purpose of the defrost cycle is that when the unit recognizes that the ice is forming the unit will work to eliminate it.
When ice builds up on the outdoor unit, air cannot flow through it. This can reduce efficiency dramatically and can even damage the unit. The defrost cycle should eliminate icing before it has a chance to build up.
How often the unit goes through the defrost cycle depends on many things - outdoor temperature and humidity, the condition of the system and the amount of indoor heat it is expected to provide.
UNITS HAVE TO BE SIZED PROPERLY FOR THE VOLUME OF AIR THEY ARE TO TREAT. IT SHOULD BE JUST RIGHT - NOT TOO LARGE AND NOT TOO SMALL. SOME HOUSES NEED MORE THAN ONE SYSTEM.
There are sensors on the outdoor compressor unit that tell it when it's temperature has risen enough to turn off the defrost cycle. This can take a while, even 30 minutes or so. Also, if the cycle is not stopped by these sensors defrosting will continue for about 10 minutes.
If your heat pump is not providing adequate heat it can be because:
- it was not installed correctly,
- or is undersized for the load it is expected to carry,
- or maybe the filter needs to be changed
- or the unit is surrounded by bushes or plants and not getting adequate air flow.
If ice build up is sudden you may be in need of a service call, or other maintenance.
During periods of frequent use, do you know how often once a month you should replace your furnace filter?
Yes! About once a month!
My recommendation: regular maintenance may reduce the frequency and longevity of the defrost cycle. Reducing the load the unit is expected to handle, like not raising indoor thermostat temps really high, or adding extra insulation into the attic space, will go a long way toward saving money and increasing the life span of the system. Good windows and doors, and good window shades and curtains, will also help reduce the heating requirement the system is expected to handle. Bottom line: maintain your system and use it properly.
Jay Markanich Real Estate Inspections, LLC 
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560
Never had or used a heat pump. My question to you is I hear it is more energy efficent than the standard heating/cooling units. Is tht true?
Think I'll check my furnace filter today.
Good morning, Jay.... I can remember 20 years ago, condo units being built and heat pump installed...new england is not a good place for heat pumps.... they are very expensive to run and not efficient....they usually can't maintain an interior temp of 70 degrees with our blistering cold weather.... single digits out today.
Jay - Unfortunately, I have seen quite a few of these icebergs when going through communities... it's just another example of home owners not paying attention to the proper operation of their home.
Knowing the capacity is HUGE ....and you can learn as you point out..it may not be HUGE enough !
Jay - living in New York not had much experience with heat pumps. But the point you made about replacing filters is very important. I do it all the time in the summer so I do understand freezing up. It is so easy to forget to change that filter.
Heat pumps are likely the most standard heating/cooling units in your area James. They are cheaper than electric baseboard or resistance. But not cheaper than gas.
That's the ticket Lenn.
Barbara - heat pumps today are entirely different than the units 20 years ago. But in your area they would have a hard time. It was 6F here this morning.
AJ - you are probably right. Seeing so many is unusual.
S&D - sizing units is a very complex calculation, so your HVAC guy has to know what he's doing.
Grant - I don't know exactly the line where the heat pump becomes less recommended. But in New York I would think they are not the best way to go.
Hi Jay,
Many home owners let alone new home buyers for the first time don't have a clue as to how often to change the furnace filter.
I am having a post tomorrow about this subject.
Have a good day in Bristow.
Best, Clint McKie
Clint - I tease people every inspection with the line I used in the post about monthly replacement. I have furnace filter posts about once a year. It is very important.
you bring up a good point that is a big issue down here in Florida, Sizing. When the unit is too big yes it will cool down the house fast but it will not have time to remove the humidity.
For that reason it is better to size an AC unit slightly too small Chuck.
Jay, Great post and an outstanding explanation of heat pumps. I have re-blogged it for some northern transplants who do not know much about their heating systems. IMHO as natural gas becomes more available here in the south, we will see the slow demise of the heat pump. It is warmer and cheaper. If I had gas available I would use it.
Thanks Tom. You might also appreciate this post:
http://activerain.com/blogsview/4193187/-so-which-is-cheaper-gas-or-electric-
Good morning Jay,
We do not see many heat pumps in this area.
Make yourself a great day.
Thank you!
With good reason Raymond. They work better when they are not covered with snow...
You are very welcome Drick.
Jay, haven't had any problems this year with the compressor freezing over. Of course heat pump efficiency is out the window with the cold weather we've been have the last couple of days.
Once a month? Geez, I better get to the hardware store today Jay. Probably should get some extras too, so they are handy in 30 days.
Everyone to Jays house this weekend 10-2 and bring a picture of your pump
It is Mike, but pay attention to the filter too.
Tom - I use the washable filters from Allergold. There are two philosophies on filters, but I prefer to keep my unit clean. You have to be really dilligent about washing them. I have had the same filters in my house for 15 years, at a cost of 3 cents per month.
'Mon over Richie! We might get some football in too. I have gas furnaces, by the way.
Jay, thanks for your explanation. Just about every home we show here in the Nashville area has a heat pump, as do we. The very cold weather we've been experiencing really makes for problems and very expensive use. As I understand it, when the outside air temp is this cold, as in the teens or less, the unit has a backup heater type element to assist getting to the desired temperature. Our heating costs really jump when it's this cold. Unfortunately, natural gas is not available where we live.
No natural gas where we are, either, but thank goodness for a wood burning stove (i.e., buck stove fireplace insert) - it heats the entire house! Heat pumps in this cold just cannot keep up.
That is the perfect climate for them Tom. My brother lives in Old Hickory. A resistance furnace inside automatically comes on to aid the compressor when it can no longer derive heat from outdoors.
Susan - that is a great way to go if wood is cheaply available! It's comfy heat!
I can immagine there would be times of very low temperatures and high humidity where it might be quite difficult for the unit to keep itself free of frost.
This caked ice means it isn't working properly to defrost once ice begins Charlie. The day of that photo it was 35F, not really cold.
It somehow looked like an Ousite unit for a centralized AC with all the ice and color now. Many people would still prefer a fireplace and wood. but HVACs can really be useful.
I had a fireplace and wood post just a couple of days ago Michael!
Jay, Thanks for the link. I have re-posted that one also. I want my friends and neighbors who think we do not need natural gas here to read it.
Tom - without even discovering more, or improving technology to get more out of where we have already harvested gas, we have enough for 120 years worldwide. In that time frame other methods of energy will be developed. At the turn of the last century, did anyone imagine nuclear? Or even natural gas furnaces?
Excellent post Jay, a few of my clients have heat pumps and I know nothing about them and want to understand them...are they really a huge improvement?
I don't have to worry about this issue, no heat pump for me.
Just because it's outside doesn't mean you don't need to do maintenance.
Thanks for explaining how heat pumps work. I see this in some listings and I had no idea how they work.
We have a heat pump but fortunately not had it ice up.
I have a heat pump. During the last few days I went out to look to see if that was happening. It was just too dang cold to stand there and look.
I have a heat pump. During the last few days I went out to look to see if that was happening. It was just too dang cold to stand there and look.
Good morning, Jay. I have a dual fuel package unit and I hear going through its defrost cycle several times during the day.
I dont' know what you mean by improvement Ginny, but as to the heat pump systems, yes there have been huge improvements over the years.
Suzanne - no matter what you have, it needs maintenance!
Joan - sometimes people think they have heat pumps and they don't!
Evelyn - that means you are doing well with your filters and the unit is operating properly.
You could tell from the inside Bill, if it wasn't heating properly. Defrost cycles are necessary - icing is not.
Michael - there is a different sound. It can last from 10 - 30 minutes.
I always felt that heat pumps up north did not work very well heating homes in the winter esp when it got very cold...
And you were right Edward! They are not as effective. Where very cold heating would be very expensive.
Interesting. I never thought about that. I am going to look at my unit tomorrow to see if there is ice on it. Thanks for sharing.
You would have to catch it during the defrost cycle Lisa. And your temps and humidity might not be such that ice can develop. But check your filter!