[Augie]

What kind of heater should we have put in?

I'm in zone 6b. 8'x12' greenhouse.

I use a cheap 1500w electric radiant heater. It doesn't keep the greenhouse "warm", but it's enough to take the edge off of bitter nights.

We had fresh lettuce and spinach last winter in spite of some extended periods of very cold weather.

That said, if you want to keep your greenhouse "warm" you'll want to install some sort of gas heat like you see in larger commercial greenhouses.

[PeterPrinciple]

That said, if you want to keep your greenhouse “warm” you’ll want to install some sort of gas heat like you see in larger commercial greenhouses.

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Go to the local heating and cooling guy and ask for a used operating high efficiency furnace that was going to be thrown away. He will most likely give you one if you haul it away.