Bought gas heater to warm greenhouse ,found it to be to expensive to run , using electric oil radiator much better cost wise ,the gas heater will install and run ,say at one degree above freezing point for emergency if electric fails .I am using Choir finding that it grows well in aquaponic system ,plat to grow lettuce in D W T system already tried lettuce growing very well ,will buy infra-red infra light to make the lettuce solid T5 grow lights just give you an open leaf lettuce I use pouches fill with choir plant lettuce then grow in D W T system seem to work .It might be an idea to grow lettuce in a different grow area rather start them in A P system the A P system provides quite a harsh enviorement for young plants.
i have been using the electric oil heater all winter, gas would be pricey. unless you had a gas/electric hot water heater and used pex line to make a inground radient heater to heat the room.