Defrost cycle occurs most often when outdoor temp above freezing & humid???

[Dave_PA]

I would appreciate confirmation of something I was told from a knowledgeable source since it is a little counter-intuitive (at least to me). It is that the defrost cycle occurs most often when outdoor temp is above freezing & there is moisture in the air, particularly on inverter units such as the Carrier 38MBRB/40MBAA. I am considering this unit due to increased 17F btuh output versus non-inverter heat pumps, and was asking how often the defrost cycle may occur overnight at about 20F. The unit uses condenser pipe differential temperature to determine when to defrost. If indeed it will defrost more at higher temp than lower temp (since colder air holds less humidity), it will not have a large impact when trying to get as many btuh's out of the unit as possible on cold evenings.

Thank you

[vstech]

It is all about runtime, and moisture in the air.
If the ambient is above freezing, but has a lot of moisture in the air… as in, it’s raining, or foggy. IF the heat is running long runtimes, it will need to defrost more often. If however, the heat doesn’t run long runtimes, the warm ambient, and moisture can prevent defrost… it’s all about how tight and well insulated the home and ductwork is.

[JayMan7]

If conditions are right, and the coil is developing ice, you can expect about 1 5min. defrost cycle per hour.

[VTP99]

You need to look at the COP (coefficiency of performance)

[BaldLoonie]

And look for a heat pump with demand defrost. Timers should be outlawed.

[JayMan7]

And look for a heat pump with demand defrost. Timers should be outlawed.

Yes they should!

I think the one he’s looking at would be…any higher end unit/good name brand should be

[R600a]

And look for a heat pump with demand defrost. Timers should be outlawed.

We are looking at you payne / bryant / carrier.