The Cold

[Mollisol]

Temp and RH in my tent. I have one inch insulation board top and bottom. My basement ducts are all open. This old brick foundation is just to leaky!

I switch to 24/0 to keep the temp up. Exaust fan set on one. I'm going to have to delay flipping or planting new until this cold snap breaks.

*humidifier set to 80%

[Gingerbeard]

Silly thought. Reading in your setup description you have an exhaust running. Maybe don't exhaust?
Maybe keep part of your tent closed to trap moisture and light heat?
Maybe cut down on fan action? Dabber said that. I would almost never recommend limiting fan action.

[dmpmfd]

Is the exhaust plugged in or on an ACI controller? Just starting out but find it easier to control tent variables even when remote.

[Bluey]

Leave the exhaust fan off, maybe cycle it for 1 minute every hour on its lowest setting. Keep good air movement inside the tent.
You could run that foil board insulation inside the tent on the walls, especially up high.

[OldManGrower]

Turn off your exhaust and open a top port on your tent. Convection will take care of your exhaust needs. I can't tell, do you have a heater? I use a small electric desk heater on a thermostatic switch. Between that and the light I have no temperature issues. The summer, that's a totally different issue.

[Mollisol]

Thanks for all the comments. I can definitely add more insulation. That's probably the simplest and cost effective option.

I guess I was worried about turning the exhaust fan off completely. It's been -2°F at night and then a balmey 20°F during the day. Especially if the sun is out.

Ill try the many suggestions. And see if I manage/regulate this temp and RH.