How to hook up a comparator

You would also want to know the heat gain in btu's for your collector and the heat load of your workshop, this would determine the differential and cfm airflow to give a good cycling time...and also a max temp control for the workshop to shut the system off...

Thank you once again Solar Eagle.

I ‘ve considered a similar setup for my own shop/garage.

I am considering the use two thermostats - I have some takeoff bimetal-with-mercury-blob type thermostats available, so there is no expense for those.

Inside is conventional close circuit when calling for heat. Outside is close circuit when calling for cold. Wire outputs in series to ‘vote’. SPST to turn off in warm weather.

Not certain the exterior thermostat can be mounted (sort of) upside down to accomplish this. If not satisfactory, I can run a relay to reverse the condition/output of the gravity switch.

This is prolly not gonna happen for me. Approx 600 sq ft room with 11 foot ceiling, doubt I can harvest anywhere near enough heat to really matter with this scheme

Thank you for this interesting read. As far as harvesting "enough" heat? When it comes to heat, a joule is a joule. For every one you harvest from a collector is one you don't have to input using alternative means?

Absolutely, a joule is a joule. If the space were heated, this would be (for me) a bit of energy savings.

This is, however, an unheated space, and raising the ambient temp from 34 F to 36 F is not considered enough to perform putter type woodshop or model train projects in the winter.

I am limited in max size of the collector, about 18 inches by maybe 10 ft. In addition, the idea of a big black box with pipes in it bolted to the garage (the front of the house) has not yet been presented to the minority stockholder (49-1/2%), and a fair amount of resistance to this practical and inexpensive scheme is anticipated.

"In addition, the idea of a big black box with pipes in it bolted to the garage"

I remember Del The Cat did a workbench creation on a solar water heater:-

https://cr4.globalspec.com/blogentry/4969/DIY-Solar-Hot-Water-Panels

I think your method is the simplest:K.I.S.S.!

What makes my idea better for me is the fact I have the take off thermostats from an install I did. These seem to be about $30 bucks USD each from varied sources.

Our OP Gavilan may not have any of these and is trying to keep the expense down. Can’t blame him, many of my day-to-day consumable items (coffee beans, socks, motor oil... ) are 50% to 100% increase in price over the past two years.

[edited - removed some whining about the higher cost of getting by. We all know what is going on]

I bought some groceries the other day,and the man at checkout had a large wart on his chin.

I tried not to stare,and said nothing.

He said "Thanks for not mentioning the wart on my chin."

"Wart?Heck,everything else around here is so high,I thought it was your navel."