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I vaguely remember the contractor who did maintenance on our ductless heat pumps two summers ago telling us not to set the thermostats of the two small heads that share an outdoor unit to different temperatures.

My memory is that there was something about the outdoor unit's inability to adjust the amount of work it's doing that made such an arrangement bad. I haven't been able to find any confirmation of this online though.

Am I making this up, or is it really good advice?

It's a two-story house, 900sqft.
(not counting the basement, where we occasionally use a radiant/oil space heater to keep the pipes thawed.)
The whole downstairs has a single double-wind heat-pump head with its own outdoor unit. Upstairs the bedroom and office each have a head with piping out to their shared unit.

The reason I'm stressing about this now is because, with both of us working from home every day, we've been mostly-closing the door of the office so we can have that one room ~10F hotter than the rest of the house during the day. (The difference is large enough that we're not much worried we'll forget and leave it overnight.)

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    I"m not going post this as an answer, since I'm not sure. I've never heard of that advice before. One of the advantages of split systems IS the ability to set different zones to different temps. I think you got bad advice and you're fine with different temp settings. – George Anderson Jan 7 at 16:55
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    It is a half truth: you could not use a split for cooling and another for heating if connected to the same compressor, this is due to the fluid path being "reversed" when heating; the compressor could be sucking mode or pumping mode, noth both. But you'll have no problem in running two rooms at different temperatures if both are heating or cooling, the extreme is that you could keep an inner split turned off and the system should work with no issues. – DDS Jan 8 at 8:33
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It's complete BS. If that was actually a problem, then the system wouldn't let you do that.

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  • LOL, you said it much more succinctly than I did. I was trying to be polite! But I agree with you completely. It's complete BS advice. + – George Anderson Jan 7 at 17:22

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