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Converted a gas station soda cooler into a smoker by adding a cold smoke generator. Now trying to determine how many watts of electric heat to add. Any suggestions?
It's 27" x 27" x 5ft tall inside with 1.5" of insulation all around except the glass door.
(Picture is too big but can't edit it on my low budget tablet at home)

Very nice - would love something like that to use as a curing chamber if the refrigeration portion is still working...

What temperature are you aiming to smoke at? How fast do you want to get to temperature? What will be the exterior temperature? If cold smoking do you actually need a heat source? The thing is on wheels so you could thermoregulate to a certain extent by moving the smoker into or out of the shade - just a thought - P

For comparison - my curing chamber, a domestic fridge, is a about half that size and has a 15W heater - if left in an unheated garage in the winter (say ambient temperature close to 0C) and left on max power for a few hours it can easily get to about 55-58C (which is when I stopped the test).

No, the cooling unit was pulled before they discarded it. I have a dedicated curing chamber made from a refrigerator with a small 100W heating element and humidifier.
I could just use this as a cold smoker but I'd rather add heat to be able to hot smoke sausage or pork butts or briskets. So up to 220F or so but doesn't have to respond quick. I'm thinking of having 2 circuits, one simple on/off (maybe 650W) and another that modulates to control temperature. I can always adjust, I'm just looking for anyone with an electric unit to get an idea of the typical power.

I don't know, but I'd certainly include a digital thermostat.

Phil

Yeah, I've got a 2 circuit thermal controller borrowed from work to maintain temperature based on a thermocouple inside the chamber.
I decided to start with a 650 watt and a 1500 watt heating element. I can change later if it is too erratic.

I have a Metro proofer that is about the same size as your unit John but it's uninsulated. It uses a 1950 watt element for heating and a 650 watt unit to heat the water pan. I've yet to do any test runs with it but it's advertised to maintain 180°f. Hope this helps, I think your on the right track.

Well, the 1500W is able to get it up to 250F pretty quick. I did a dry run over the weekend. Still have to figure out the controls for adding the 650W booster element.
Unfortunately as in all projects, that only highlighted the next problem. The adhesive that holds the gasket track to the steel door didn't appreciate the heat. Once it got over 220F the contact cement got gooey again and when I opened the door the gasket fell off
Oh well, if it were easy, everyone would be using gas station beverage coolers for smokers, right?

Clean off the glue with alcohol and use rtv. It will keep the gasket in place. I use a rope style gasket like the ones used on a wood stove, hasn't moved in 15 years. My smoker is about the same size and I'm down to 450 watts and runs just fine. Too much heat to fast and case hardening would occur. I'm using scr's to control everything.