Dehumidifier problem
You have a ventless gas heater problem. I would strongly suggest using a vented (preferably 
"sealed combustion" with an outside air intake as well as an exhaust) rather than a ventless heater which dumps combustion byproducts, including a great deal of water vapor into your living space.

You can set a dehumidifer at 50%, and it will probably help, if it keeps up with the problem (i.e has adequate capacity), but it's treating the effect, rather than the cause. 

Or use a cold-climate air-air mini-split heat pump, which may be cost competitive with gas heat depending on your local gas and electric rates, and which also will not dump water into your air.