Heat Pumps and Electric Heating - bang

What causes a geat pump to 'bang' only when it is very cold out?

Is this a continual noise or only when it starts or stops?

This bang is normal. It is caused when the hot gas recycles in the
compresor, no ned to worry if unit dosnot ice up in very cold weather..............

This bang is normal. It is caused when the hot gas recycles in the
compresor, no need to worry if unit doesnot ice up in very cold weather..............

This bang is normal. It is caused when the hot gas recycles in the
compresor, no need to worry if unit doesnot ice up in very cold weather..............
Could you explain this for those of us who dont understand?

This bang is normal. It is caused when the hot gas recycles in the
compresor, no ned to worry if unit dosnot ice up in very cold weather..............


>>Thanx alot for the info Buck. It is very loud so we thought something was wrong. We checkrd for loose ducts and tin panel that could bang with a change of air flow but all is tight. Apreciate it.

For clairification, please define "very cold". To some, it could mean 40º & to others -20º or colder. Also, as I asked before, is it just a one time bang or does in continue during the cycle.

For clairification, please define "very cold". To some, it could mean 40º & to others -20º or colder. Also, as I asked before, is it just a one time bang or does in continue during the cycle.


>>It 'seems' to occur occasionally when it is below 30 but never in the forties. It doesn't do it often either, maybe three or four times a week in the winter(Maryland-as far north as a heat pump will do much). There is no pattern. The service man stopped and started it and the blower but could not cause the bang. The unit is about 20+ years old and the blower has a single speed. I asked the question because it really is loud like if you kicked the side of the heat pump. I thought it was a wobbly duct but after riveting some steel strips on any wobbly ducts or panels(I forgot the name of them), there are no loose places. I suspect we will be replacing it soon but who knows. It is 15 degrees this a.m. and 70 in the house-no noise so far at this temp.

For clairification, please define "very cold". To some, it could mean 40º & to others -20º or colder. Also, as I asked before, is it just a one time bang or does in continue during the cycle.


>>It 'seems' to occur occasionally when it is below 30 but never in the forties. It doesn't do it often either, maybe three or four times a week in the winter(Maryland-as far north as a heat pump will do much). There is no pattern. The service man stopped and started it and the blower but could not cause the bang. The unit is about 20+ years old and the blower has a single speed. I asked the question because it really is loud like if you kicked the side of the heat pump. I thought it was a wobbly duct but after riveting some steel strips on any wobbly ducts or panels(I forgot the name of them), there are no loose places. I suspect we will be replacing it soon but who knows. It is 15 degrees this a.m. and 70 in the house-no noise so far at this temp. It only bangs once.

From what you write, I get the impression the noise is from the air handler or ductwork rather than from the outdoor unit. If this is the case, the source of such noises can be really hard to find. If the ducts are in an unconditioned space, it could be simple expansion/contraction due to the temperature difference between the duct & the air coming thru it. If you have changed to one of the pleated filters from a fiberglass one the extra restriction can also cause problems.

From what you write, I get the impression the noise is from the air handler or ductwork rather than from the outdoor unit. If this is the case, the source of such noises can be really hard to find. If the ducts are in an unconditioned space, it could be simple expansion/contraction due to the temperature difference between the duct & the air coming thru it. If you have changed to one of the pleated filters from a fiberglass one the extra restriction can also cause problems.

>>When I moved in, there was a 25x20x1 pleated filter in the unit so I've been using the same ever since. When I was in Fl. a tech told me not to use the ?plastic filters that you wash in my ac unit. Is that what you are referring to? Should I be using a special filter for an air pump?

By a fiberglass filter, I mean the cheap ones (3 or 4 for $2 at home centers). The pleated ones come in different MERV ratings & the higher the MERV rating, the better job of filtration they do but also the more restriction to air flow they create.

I use a Home Depot Pkg of three which has a merv rating of 8.
Thanx for the help.

I don't think the filter is your problem. I think it has to do with the temperature of the duct versus the temperature of the air going thru it. Does any of the duct work go thru an unheated space such as the attic or a crawl space?

No, all the ducts are in a heated area.

Noises, particularly duct noise can be real tough to track down. I don't know where to tell you to start other than watch the duct for any obvious flexing. You can go along the main duct & push gently to feel for flimsy spots.

Well, if it is only a flimsy duct that is good news b/c the noise happemns only occasionally when it is in the twenties. If it is a bigger problem I guesss it will let us know. It is an old timer like me and has to say ouch sometimes. Thank you.