I have a 5 ton Bosch air to air heat pump, just installed last fall. I built a small timber framed cover to protect it from snow. One thing I was hoping to also do was to cover the sides of the small building in the winter to block the wind and snow from entering the area, but leaving the front open for air movement ( the back is against the house). It is about 2 feet from the house sitting on a couple 6 inch stand offs.

Would covering the sides to protect from the elements decrease airflow too much?

I am hoping to get the most out of this thing this winter and I think this could help a lot.

  • The manufacturer's installation instructions should prescribe acceptable airflow restrictions. Have you already looked at the installation docs?
    – popham
    Commented Oct 11, 2023 at 17:23
  • Wouldn't wind hitting it increase the efficiency? That's just free heat you're not paying to actively capture. Air-temp water contains 900x more heat than air, so it's even better. Seems misguided, but you can easily test it yourself this winter with a removable barrier; see if the furnace runs more with or without your restriction.
    – dandavis
    Commented Oct 11, 2023 at 21:27
  • @dandavis In heat mode, it's chilling the outside coils to below water freezing temp, so water getting directly on the coils will coat them with ice. That will necessitate a defrost cycle. Commented Oct 11, 2023 at 22:22
  • @Harper-ReinstateMonica Heavy rain would melt accumulation, but there's a band of time/temp curve where freeze-over could be hard to avoid. Would inverter models be able to throttle back to just before freeze-over to prevent that? I've heard they need less frequent defrost, maybe that's why?
    – dandavis
    Commented Oct 11, 2023 at 23:01
  • @dandavis the problem is if it's anywhere near 32F outdoors, the coils have to be significantly colder than 32F to transfer heat at any reasonable rate. Commented Oct 12, 2023 at 8:20

1 Answer 1


The wind is the same air you're pulling heat from anyway. A "small" structure seems likely to impede air-flow if it's got sides.

Keeping the snow from falling on it with the roof might have some benefit. Might cost you some efficiency when it rains, though.

Protecting it from the "cold wind" only works if you have a handy source of warmer air - otherwise the job of the heat pump is to make that air even colder, which is how you get heat. Wind chill only affects things that are warm, like your skin. To a heat pump, it's all the more air it can make colder, to make heat.

If you get enough snow to make a roof and your installer only mounted it 6" off the ground, I can't respect them much. My installer used 18" legs... which are usually enough to keep from having to shovel around them.

  • Wind chill affects things that are wet, same with heat index. That's why it's not the same for cats and dogs as us; they don't perspire; they have to pant.
    – dandavis
    Commented Oct 11, 2023 at 21:25
  • We usually get a few feet of snow for the year, last year I had a pile all the way around the unit with a 2 foot gap. It was very hard to keep up with the snow fall. Part of the reason for this structure is to protect the unit and the lines going into the house, having hundreds of pounds of snow fall on either of them sounds like a bad idea
    – Markpelly
    Commented Oct 11, 2023 at 22:00
  • If it's near the wall and the wall has eaves above, also bad placement. Hundreds of pounds of snow falling from the sky as flakes is no big deal. Putting a compressor unit where the snow & ice dumps off a roof in large chunks is a big error, IMHO. Near a gable end is fine.
    – Ecnerwal
    Commented Oct 11, 2023 at 22:05
  • Yeah this is placed just under an eve over hang. This replaced a unit that was there for 40 years (AC only before) and it seemed fine. It is a pain that I need to be careful of roof raking on this unit but we are limited to where the unit was placed anyways. I appreciate the useful feedback!
    – Markpelly
    Commented Oct 15, 2023 at 14:58

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