How much are mini-splits really affected by altitude?
I’m sizing a heat pump mini-split for my 20×20 garage, which has been pretty well air sealed and insulated with closed cell foam. I’ve had a series of installers out and the recommendations were all over the place, ranging from 12k to 18k BTU, and from $3k to $12k.
Two of the companies actually bothered to do a load calculation, and I tried it online as well – but those numbers had a broad range, too.
Putting them all together, I would guess that I need roughly 6k Btuh cooling and 22k of heating (although, one of the results had the cooling at 4k and another had the heating at 49k!). I am using these numbers because the installer who really took the time to get into the load calculation produced those numbers, which fell between the other two results.
Now, I can look at different models (like the Mitsubishi & Fujitsu) and choose a size. One thing I don’t understand, however, is how altitude plays into this. I know that mini-splits have reduced capacity at altitude, but how much would one typically deduct from the ‘perfect world’ capacity of a minisplit to account for altitude?
Is there a formula for this? I’m at around 5350 feet. thank you!