40x60 shop, electric heater for freeze protection

[Peace Meal Farm]

I am in the process of insulating my 40x60 quonset. It is tin with sitting on 6" laminated wooden ribs with 1.5" (2x4) strapping. Floor is non-insulated concrete. I am starting off my insulation journey with 1.5" of spray foam - enough to cover the strapping.

Primary heat is a RSF 65 t-stat controlled wood heater. While I have natural gas to my house on the property, I do not yet have gas to the quonset and this is unlikely to change for the next couple years.

For both insurance purposes and for freeze protection (think week-long holidays) I am likely to install some redundant electric heat. I am thinking somewhere between 20 000 and 30 000 watts at 240 v.

Is there benefit to running a single 20 or 30 k watt heater vs using 3x 7 500 watt heaters?

[ghfalls]

Is there a reason you don’t want to go thicker on the spray in? Seems like if they’re there already spraying, that going thicker wouldn’t be a substantial extra cost?

[Peace Meal Farm]

Originally Posted by ghfalls

Is there a reason you don’t want to go thicker on the spray in? Seems like if they’re there already spraying, that going thicker wouldn’t be a substantial extra cost?

Yup - cost. I have about $40k budgeted to pull this off at moment and this is what I can afford.

[crazy_davey]

Pretty sure if spray foaming it's recommended to go at least 3-4". Got 4" for my shop roof and gables and that's the least I would go.

[Peace Meal Farm]

Not saying this is the end of the line as far as insulation goes. Spray foam can be added to with ease. My goal is to pull this project off without debt, and if that means a winter or 2 with less than spec insulation then I am okay with that. 1.5 inches may not be 4, but it is better than zero

My main heat is going to be wood stove, fed by off cuts from my mill. Cheap heat.

Mostly I want to know any ups and downs regarding 1 large or multiple small resistive heaters for my backup/secondary heat.

[Dewey Cox]

I think the 1 1/2" sprayfoam is a great idea.
That will seal things up, and if you want more r value down the road, you can put batt insulation between the ribs.

If it's just for backup, I'd get a couple of those 240v construction heaters. They would be handy to have around/easy to sell after you put in permanent gas heat.

[dewalt18]

Just for curiosity sake, how far is the shop from the house/gas meter? Cost way less to run gas than you might think, if you’re willing to dig the trench.

[Peace Meal Farm]

Originally Posted by dewalt18

Just for curiosity sake, how far is the shop from the house/gas meter? Cost way less to run gas than you might think, if you’re willing to dig the trench.

Current house is living on borrowed time. New house is 8n the works, looking to build over the next 2 years. When gas, water and sewer gets moved from the old house to the new then I will trench gas to the shop at the same time.

[roy9525]

I have the same amount of spray insulation in a 24 x 36 shop and is kept warm by a 6500 watt 240 volt heater. A ten thousand prob keep it from freezing worries

[Peace Meal Farm]

Originally Posted by roy9525

I have the same amount of spray insulation in a 24 x 36 shop and is kept warm by a 6500 watt 240 volt heater. A ten thousand prob keep it from freezing worries

Beauty. Thanks for the feedback.

[brslk]

I used to rent a shop out in the country about the same size. A single 10,000 watt heater kept it well above freezing in an emergency. My place had less insulation than that, so you should be good to go

[canuck]

If I may hijack the thread for a moment...
For those of you who have sprayfoamed your pole shops, did you foam the underside of the roof tin as well as the walls (exposed rafters)? Or do you need a ceiling structure to spray onto?