Electric Unit Heater in Greenhouse

[mkgrady]

I am trying to determine how to size an electric unit heater in a greenhouse, or at least have someone confirm my heater choice. It is in a school on Mass. The room is 17'x25' with a sloped ceiling that averages 16' high. The only glass walls facing the elements are the south side and the roof. The north wall is part of the heated building and so are the east and west walls. I have no idea how to size the heater.

I have a 20 amp, 208 volt, three phase circuit that is available. I have found a couple of unit heater models that put out 17,000 +/- BTUH, 350 CFM that could be put on the available circuit. Will this size be adequate? If not, what would be a better choice?

Thanks, Mike

 

[VUGear]

Shouldn't this be in an HVAC forum? Just sayin'...

 

[mkgrady]

Shouldn't this be in an HVAC forum? Just sayin'...

I don't know. It is electric heat... An HVAC contractor wouldn't have a roll in the installation being all electrical. I figure another electrician might have some valuable input.

 

[donselectric]

figure 10 watts per sq ft and a ceiling fan and you should be golden...
it maybe hi but you can always turn it down.
i put a 240v 12000w space heater in a crawl space 30x40 to prevent freezing of
pipes/traps and they tell me it worked good course it was set at 40deg but no sun either...

jmo

 

[mkgrady]

figure 10 watts per sq ft and a ceiling fan and you should be golden...
it maybe hi but you can always turn it down.
i put a 240v 12000w space heater in a crawl space 30x40 to prevent freezing of
pipes/traps and they tell me it worked good course it was set at 40deg but no sun either...

jmo

The room is 425 sf and I'm putting in 5,000 watts so that sounds good. The unit heater has a fan built in so I'd skip the ceiling fan. This will only be used spring and fall. In winter they have a hot water system running off the main building boiler

 

[steve66]

I'm not a mechanical engineer, but that sounds way low for a glass building with a steel frame, and no insulation, that may be 30' tall.

But wouldn't it depend a lot on what part of the country you are in. And how warm do they need to keep it? Are they going to grow stuff in the winter, or just keep the pipes from freezing?

STeve