Juz sayin but what you are claiming does not make sense
If you have a VENTED heater, the only affect it will have on humidity is whatever combustion air it draws in that infiltrates from OUTdoors. So indoor humidity will be affected by cold dry (if it is dry) air coming in from outdoors. When you heat a cold room (and there is "no" outdoor infiltration) relative humidity decreases with heat. But the "actual" total water content does not change
If you have an UNvented heater such as a torpedo or infra-red, that will ADD humidity because the products of combustion contain humidity--and lots of it
I don't know anything about POR-15 and humidity but if you really do need more, you could do something like a hotplate and a big pan of water and just heat/ boil it into the air