Heat Pumps in a Top 10 All-time Snowstorm

We have about ~75 cold climate heat pumps deployed this year. Here's how they did.

What it looks like after 18 inches of snow in Acton

It’s official. After 20+ inches in parts of the Boston Metro area, the January 25th snowstorm of 2026 is a TOP 10 snowstorm in Boston history.

Courtesy of CBS News

I was here in college back in 2015. Walking around this week, I’m reminded of 2015. These days, however, we have cold-climate heat pumps. And every heat pump we install has a defrost mode, which reverses the refrigerant cycle to heat up the coil & defrost the ice.

We’ve reported on heat pumps in heat waves. So how’d they do in the winter?

Vast Majority of Heat Pumps Powered Through

Before & after defrost mode, in Arlington. This is normal.

Shortly after the storm started, I sent an email to nearly everyone who we did a heat pump installation for back in 2015. That accounts for about ~75, maybe 80 outdoor units out there, a mix of LG, Daikin, and Mitsubishi.

Out of those units, we had about 5 7 condensers that iced up to a point that standard defrost mode could not get out of. That’s about a 90% up rate in a top 10 historical snowstorm (followed by a week of bitter cold temps reaching 0°F), with Mitsubishi & Daikin having an edge over LG in terms of keeping things going¹.

Here are 2 units in Ashland (Daikin and LG, I should mention), with photo #3 of what it looks like pre-defrost, and #4 and #5 post-defrost for Daikin & LG, respectively:

LG had the advantage of a drain pan heater, but it seems like Daikins overall had fewer icing incidents

During massive snowstorms like this, it is highly advisable that you remove snow from underneath the stands. The stands exist for a reason, but if you’re out in Gloucester/Ipswich & ended up with like 25 inches (!!) of snow, it’s going to go past the stand. Obviously, defrost mode doesn’t work very well if your unit is buried in snow.

Here’s what defrost mode looks like in a video with a temperature gun:

And here are a few more outdoor units in the wild, all of which are fine:

Woburn, Arlington, and Somerville

What if my unit completely iced up?

In particularly icy conditions (or if your unit just happens to be directly underneath a roof that’s dripping freezing water), the entire back & sides of your heat pumps may be frozen. And that’s a situation where defrost may not be able to completely de-ice all by itself.

Here’s how that looks like:

Now, in a situation like that, what do you do?

• One option is to run the heat pump in reverse (AC mode), so the coils really heat up. This is a bit of a manual defrost option, if you will. However, this does require for you to at least have some airflow through the back of the condenser, which won’t happen if it’s completely frozen in the back.

• Another option is to use room-temperature water (not hot!!) to defrost the ice.

Now this is the part where I give the disclaimer

If you ever find yourself manually de-icing a condenser with water, do not use hot water because the temperature difference between the coils & the temperature may cause the coils to crack via. thermal stress.

In reality, you don’t even need warm water to do it. For science, here’s how standard tap water (~50 degrees or so) fares vs. a thin sheet of ice on the small, tiny fins².

Before:

During de-icing:

That video was filmed when it was about 10 degrees outside. The other 3 out of 4 outdoor units here for this building was completely fine via. standard defrost (i.e. no manual intervention on our part). Here’s how that looked:

How was the rest of winter?

Up until this snowstorm, all units except for 1 (which was under a slanted roof with no gutter, directly under runoff during a frozen rain day) had no issues with defrost.

Is there anything I can do to prevent snow?

Actually, yes - you can install a snow cover. Like this one:

Or like this one³:

While this won’t help if your outdoor unit is in a windy spot in an alley where snow gets whipped up on the regular, or from frost accumulating simply due to the humidity, it will help shield some of the snow from above.

How snowy is it out there in Cambridge?

I thought you’d never ask. But here:

Takeaways

If there is a potential Top 10 all-time snowstorm on the forecast, keep an eye on your heat pump as the snow builds up, and please shovel the snow from underneath the stands if it starts to pile up past 1 ft. After the defrost cycle, the melted snow/frost needs to drain down the bottom, and if it’s covered in snow, it can’t do that.

Alright, stay cozy out there, everyone. I’ll update this with a few more photos & videos as I get them.

The icy view from Logan airport

1. Or maybe there is a Mitsubishi or Daikin unit out there that’s struggling, and I just haven’t heard about it.

2. Coils vs. fins: coils are the big pipes, fins are the small metal things.

3. https://www.reddit.com/r/heatpumps/comments/1qr8kda/mitsu_just_chugs_along_at20c_without_issue/