Depends on how large, "large" is? That particular heater has a BTU output of 80,000 to 200,000 BTU's. That's a lot of heat. I suspect if you have a way to move the heat around some (like ceiling fans on slow speed), it would do an adequate job of keeping plants warm. But, keep in mind, this is not a Vented Heater. So, with that high a BTU output, you would need some makeup air. That way any residual fumes won't damage or kill your plants or you.
This type of heat is a moist heat. That's felt very quickly. So as far as "large" is concerned ... at 80,000 BTU's, "large" needs to be at least 1200 sq ft, with some minimal fresh air input & air movement. Of course, during the day light hours, you could turn the heat down considerably and let the sun heat the green house. That would save on gas consumption too.
Answers & Comments
Depends on how large, "large" is? That particular heater has a BTU output of 80,000 to 200,000 BTU's.
That's a lot of heat. I suspect if you have a way to move the heat around some (like ceiling fans on slow speed), it would do an adequate job of keeping plants warm. But, keep in mind, this is not a Vented Heater. So, with that high a BTU output, you would need some makeup air. That way any residual fumes won't damage or kill your plants or you.
This type of heat is a moist heat. That's felt very quickly. So as far as "large" is concerned ... at 80,000 BTU's, "large" needs to be at least 1200 sq ft, with some minimal fresh air input & air movement. Of course, during the day light hours, you could turn the heat down considerably and let the sun heat the green house. That would save on gas consumption too.