8-10 degrees of thermostat variance?

Howdy all, hope everyone had a great turkey day!

Soooo, I started the initial build of my keezer yesterday, I picked up the magic chef 7.2, and had ordered this thermostat:

Weatherproof Line Voltage Greenhouse Thermostat

After getting it all wired up, I hung my digital probe thermometer and found that the variance on this particular mechanical thermostat seems to be in the range of 8-10 degrees ambient air temp.

I did a search on existing thermostat threads, and will be trying the glass of water trick tonight, though I did throw some beers in there yesterday and was monitoring the temp throughout the day, and managed to get it dialed in to around 42.

I guess this is a long way of asking. Does anyone else use this thermostat? Is 10 degrees of variance too much? I am just concerned about the temperature variance once a load gets put on the freezer. Those that do have a ranco, what is your variance set too? Should I just save myself the headache and buy a digital thermostat?

Thanks in advance!

As a side note, this forum is fantastic, I started brewing about 5 weeks ago, and while I have made some mistakes, I have avoided many many more by soaking up the info here. I have 5 beers in the pipe, including my first one. Ha! A red ale, Rogue dead guy, Guiness clone, a dunkel, and a Redhook ESB clone. I think I'm gonna pick up another carboy and fire up the apfelwein for the wife.

10F is excessive for brewing, but in line with my experiences with greenhouses. For fermentation, my Ranco is set at 2F and that is in a refrigerator. My kegger is a freezer and the temperature variation is 4-5F, even with the Ranco set to 2F. The kegger turns on, runs until the Ranco sees a 2F drop and shuts off. But leftover coolant drives the temperature down a couple more degrees.

It sounds like you were originally running it with an empty freezer. Without any thermal mass inside that freezer (ie beer bottles, kegs), you are going to see greater fluctuations in temperature as the freezer and thermostat struggle to keep just the air to temp. With a few kegs in there (once they get chilled to your set temperature) temperatures should stabilize with about 4-5 temp variances like David said.

When I pop in a fresh keg I just filled, my fridge will cycle a bit more than normal as it gets that keg down to serving temp. After the keg is adequately chilled, it cycles once every hour for 5-6 minutes like clockwork for maintenance.

Also, that temperature controler is designed for greenhouses, not freezers. With this in mind, it may not be as efficient as a Ranco or Johnson unit. However, I am sure it will be fine for your kegerator.

Good luck and remember... relax, have a homebrew.