Portable Heat Pump Mod For Subfreezing Weather

Can a portable heat pump work in very cold or subfreezing weather (much below 40F)? I searched thoroughly and found that all portable heat pumps are rated to heat only when the outdoors temperature is around 40F or above. In my previous review of this Whynter ARC-1230WNH heat pump, a significant limitation was it would not heat if the outdoor temperature dropped below 37F (its manual specified 41F). This greatly limited its usefulness as a heater in New Jersey, where temperatures can drop to as low as 5F in winter and it frequently dips into the 20’s at night.

By contrast, most split system heat pumps (mini splits and regular ducted split heat pumps work to near or much below 0F.

I found this discussion online where Deizel_Dave discussed modifying his portable heat pump by relocating its outdoor air temperature sensor from the air intake path to indoors to prevent the unit from turning off heating, causing it to continue function in temperatures much below 40F. The only issue he observed was that the condensate output increased when running the portable heat pump at very low temperatures.

I wanted to give it a try. If it didn’t work, my plan was just to put the sensor back in its original location. I estimated that if the unit then would heat with outdoor temperatures down to 32F I’d be able to greatly extend its use as a heater.

My Unit(s)

Whynter NEX Inverter Portable Air Conditioner & Portable Heater ARC-1230WNH

Results

It Works! So far, I have tested it to an outdoor temperature of 10F, and it still heats! On a couple of nights when the outdoor temperature dipped to 25F, I used a Kilowatt meter to compare the energy draw of the heat pump with an electric space heater, and even with those low temperatures, the heat pump put out more heat and used less than half the energy compared with the electric space heater.

Like all heat pumps in heating mode, their efficiency decreases with decreasing outdoor temperatures. The colder it gets, the less heat it produces, but it still puts out a surprising amount of heat, even at 10F.

Convinced of its effectiveness, I bought a second portable heat pump for downstairs. The “portable” unit is very heavy and bulky. It is easy to wheel it from room to room but a beast to get up and down stairs (77lb, oddly shaped with thin, vulnerable outside cabinet components which could break if supported incorrectly while lifting or moving with a hand truck). This second purchase was prompted by the mini split heat pump in the house’s addition failing due to running low on refrigerant during a prolonged deep cold wave (several weeks). The portable heat pump enabled me to heat the addition to the 70s during a day in the low 40s, in order to run the mini split in A/C mode to recharge it.

Warning

• I expect doing this will void your warranty
• This will cause your unit to operate outside its intended parameters and possibly shorten its life or damage it. (Although I have not observed adverse effects yet)
• Although it has been working fine so far, there may be conditions or situations where this might cause problems I am unaware of.
• I am reporting what I did and what happened. If you do it, it is at your own risk.
• I have seen reports that my unit is a rebranded Midea unit. The tests I did are on this specific Whynter unit, and I have no way of knowing if you can extrapolate these results to other units.

How Much Condensate?

Our main ducted HVAC system results in a temperature difference of several degrees between the upstairs and downstairs. Also, the main systems thermostat has a nightly setback temperature to save energy. The first unit only gets light use. It is in an upstairs bedroom as a supplement to heating and cooling. Both the upper and lower drain hoses are directed to a 1 gallon Arizona Ice Tea plastic bottle. Under these conditions practically no condensate drains to the bottle.

The second unit used as the only heater in the addition, running continuously with daytime temperatures around 35 and nighttime temperatures around 23 produced about 1 quart (1 liter) of condensate in 3 days. The portable heat pump had no difficulty heating this 400 sq ft area.

How to Move the Outdoor Temperature Sensor