FR255/s Heat and Altitude Acclimination

FR255 has no heat acclimation, unfortunately

Yes, you're supposedly right. However... from time to time I get heat acclimation updated after some running or trail activities. And, if I rest for a few days afterwards, it also updates daily with decreasing values. From my experience, it actually looks like the watch supports heat acclimation but with an erratic behavior.

BTW, every time I go for a bike ride with my Edge 830, heat acclimation gets recorded on Connect.

Do You keep the spo2 ON ? where do you see those values on the watch?

What do you mean by spo2? And I see those values on Garmin Connect.

is the pulsoximeter

ah ok. Yes it is on, but taking readings only during sleep. Why do you ask?

well, I bought my fr255 2y ago and never had readings about heat acclimation so that's weird , I keep the pulsoximeter off so maybe that's the reason

That's strange, the manual says differently and there is no answer from garmin. 

When you say "there is no answer from garmin" , did you contact support. This is a user forum so most times you won't see an answer. I've found support quite helpful when contacted.

If you are seeing it in Garmin Connect, do you have any other Garmin devices like a bike computer? Edge devices have heat acclimation.