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Community and Q&A

Retrofit drain pan heater

Jay Thomas | Posted in General Questions on

I have a Pioneer/Midea heat pump with no drain pan heater. Seems to work well enough in my climate zone but when we have a sub feezing week I do have some ice build up.

Last time I used a heating pad to clear it and it was effective. (And raised COP quite a bit) I think an engine block heating pad may work better. Anyone try something like that? I could put it on a thermostat and gfci outlet without a lot of work.

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  1. Expert Member
    Zephyr7 | | #1

    Depending on the size of the pan, the engine block heater is probably too big. You need only enough heat to stay in the happy range for your equipment. Engine block heaters usually try to maintain somewhere between 80 and 120 degrees F which is much higher than you need for your application, so you end up wasting energy. You might have better luck with a short section of self regulating heat tape (raychem makes a good one).

    Another option, if you have electronics skills, is to use a “metal clad” resistor of suitable value as a heater. These resistors can be mounted with two screws and are designed so the flat mounting surface acts as a heatsink. I’d recommend using a transformer (like a 24v bell transformer) to run the resistor on low voltage for safety. A 25 ohm resistor running on 24v will give about 24 watts of heat, continuously, so use a 100w resistor to make sure you get long life. I’ve done things like this before and just use a thermostat to turn the system on and off based on outdoor temperature. Simple and reliable.


  2. Jay Thomas | | #2

    Thanks! Great ideas. 50-100 watts seems like enough to avoid frost for a few extra degrees which makes a big difference in performance

  3. Alan Afsari | | #3

    For Fujitsu, I was comparing three different outdoor units, all are 9k btu units (each paired to different indoor units- wall (-15deg F), floor (-15deg F), and ducted (-5deg F). The cold weather models have move holes - I assume to drain easier.

    I don’t know what goes into designing these, but I would think that from a supply chain stand point- they would design one regular and one cold weather 9k outdoor unit that can mate with any of the indoor 9k units...

    Do you think trying to either order a cold weather pan to install as an aftermarket change or drilling more holes in the regular pan would help? (Or void the warranty?)


  4. Jay Thomas | | #4

    Probably a good idea but I didn't see where to get one for Midea. Plenty of generic ones out there... they just look like 75-100 watt heating wires inside the frame.

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