I have a 9 year old Modine 200K BTU heater in my GH that won;t fire up because the pilot has rusted and is going to have to be replaced. Thankfully, the weather is still pretty warm here....60-70F at night for the next 10 days at least. We are actually more likely at the moment to be hit by Hurricane Eta than have a cold snap. I have ordered the part I need from Modine and have a repairman to install it.

But was wondering....if I ever had a heater failure, and couldn;t get things fixed right away, what would be the best way to give my GH emergency temporary heat?

Its 1740 sq feet with a ceiling that is between 16-20 ft

Oh gosh. You have so much space that you really need that industrial heater. I guess you could use a bunch of the electric small heaters for home use. I have a 15ft dome greenhouse, and one little heater works well. Maybe you'd need 10 or 15 of them!!!