Heating a greenhouse.
It has gone down to 36F once, under 40F for about a week so for the first time the heating system in my relatively new greenhouse has been in full use. Kept the temp at 60 all the time without problem. It's the quality of heat that I wish to discuss.
I circulate hot water from my house hot water heater to an industrial copper radiator which has 2 fans pushing air through it. A thermostat turns on the fans and the circulating water pump when the temp drops below 60F. It has not adversely affected the hot water use in the house. All the pipes to and fro are insulated to prevent heat loss.
A friend of mine has a greenhouse which is heated with the conventional natural gas burning heater. It works fins and keeps his plants warm, no problem. We both have noted a difference when you go into the GH in the morning after a night of heating. I can't find the right words to define it but the warm air in mine feels 'nicer' than his. Its a comfortable enveloping heat with humidity which is simply not the same in his greenhouse. Other factors are also at work as the 2 structures are not the same.
The difference is subtle and neither of us would consider for a moment changing his heater, both of us however agree that in a future GH, we would use hot water to heat it.