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Question DetailsAsked on 2/9/2018

My Lennox heat pump(the outside unit) is covered in ice! Is that normal?

My Lennox heat pump(the outside unit) is covered in ice. I just got my electric bill and is doubled from the same time period last year (it has been about 5 degrees colder the January). Is this normal or just I have it looked at?

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2 Answers


Assuming this is not from accumulated snow or ice/water from the roof, sounds like the defroster coil or its controller board or sensor has gone out, or possibly your unit has a refrigerant fluid leak.

During heating use the outside coil can freeze up just like the indoor coil does in summer A/C use. The indoor coil they just let defrost naturally from indoor heat between cooling cycles, but the outdoor coil running in the winter cannot melt off in air temps significantly below freezing, so it has to be melted by a heating coil (or with a very few units reversing the operation to A/C for a short time to heat the coil with warm fluid). Because a good portion of the heat pump heating (aside from the auxiliary heating coil to add more heat in cold weather) is taken up from the outside air through the outside coil - which if frozen up cannot let air through it, so the heat pump does not collect the energy from the air it should.

This means the auxiliary electric heating element in the air handler will then be making up the difference in heating demand by providing most of the heat (the rest from friction in the compressor), so instead of an operating efficiency of maybe 2-4 with the heat pump operating (down to maybe 10-20 degrees anyway), the heat strip heating will be operating anytime heat is called for, with an efficiency of about 1.0. So you can get roughly a doubling to quadrupling of electric operating cost for the heat pump in heating mode - or commonly about 100-300% higher total electric bills for your house if your heat pump is not properly generating heat. Ditto if the outside temp drops the effective operating temp of the heat pump unit - as high as around 35 with some units, more commonly round 15-20 with many units, you can get at least minimal heat pump heating as low as around zero with a very few units. Generally, below about freezing outside temp, at least a third to half the heat from the system is being generated by the electric heating strips (or auxiliary gas heating unit or furnace if you have that) instead of the heat pump.

Another factor - the efficiency of the heat pump in pulling energy from the outside drops from a factor of maybe around 4 (so it is "stealing" energy from the outside air at a rate of about 4 times as much energy as the unit is using in electricity to do that) at say 50 degrees or so ambient temperature, down to typically less than 2 below freezing, and to near zero around 0-10 degrees or so - so if your 5 degrees colder than last year means yuou are getting into the low teens or especially single digits, most or almost all your heat may be coming from the heat srips.

Of course, if (because the heat pump was not putting out enough heat) you turned the thermostat to emergency heat, then the efficiency is about 1 - so the electric heat strip would be taking maybe double or more the energy as usual.

Heating and A/C is of course the Search the List category to find well-rated and reviewed companies to send out a tech to check out your system and figure out wht is happening.

Should the problem turn out to be a coil failure or leak in a coil, be prepared to consider the value of repair versus replace, especially if this unit is older (meaning maybe over 8-10 years for a heat pump, which have normal life of maybe 10-15 years if you are lucky).

You can find a lot of previous questions with answers addressing the repair versus replacement issue, and the additional cost effect if your unit is an older R-22 (Freon) unit, in the Home > HVAC link, under Browse Projects,at lower left.

Answered 2 years ago by LCD


Bad defrost board...

Answered 2 years ago by CAC1819274

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