Space Heating Upright Freezers Compared to Chest Freezers

For the past year, I've been using chest freezers, as a fermentation vessels, in my garage. I recently converted one to a keezer and purchased an upright freezer on CL to replace it.

I use two-staged, Ranco controllers to monitor my temps since the freezers remain in a Connecticut garage year-round. Stage one controls the freezer and stage two controls a Brewer's Edge Heating Pad (the sticky-mount kind).

It' starting to get very cold here and the space heater can keep temps in my chest freezer around 64 degrees. I added a second space heater to see if I could get the temps even higher. I can — 85 degrees.

I tried the same experiment with my upright freezer. With one space heater it could barely get to 60 degrees. With two space heaters inside the upright, temperatures only got to the mid-60's.

Is this common? Are upright freezers not as insulated as their chest counterparts? I was hoping to use the upright as my primary fermentation vessel with temps ranging from 68-85 (I do Belgians from time to time). I don't think this is going to be possible in the winter and I'll have to use the upright as a secondary chamber with temps around 62-64 degrees.

A bit about the freezers: the upright freezer is a 19.5 cu ft, older, Sears Coldspot (2354). One of the marketing terms used for it was "thin walled." The chest freezer is a 14 cu ft., Kemore that seems to be less that 7 years old.

I just bought this heater at Target for $15. I use it in my Upright 17cu ft freezer and with the thermostat set on HI 65 degrees, it keeps my freezer at 62.5 (which is what I where I want it). The thermostat goes up to HI - 80 degrees so I imagine that it can go higher if you prefer. You can set the temp on 60 - 65 - 70 - 75 - 80 (HI or Low fan)