I am looking at setting up some equipment in order to better regulate fermentation temperatures and have been looking at the system available from northern brewer which consists of the fermwrap heater, a temp controller and a stopper thermowell. My question is regarding the thermowell as I now usually utilize a blow off tube and regularly need this so if I was to move to the thermowell how do I stop blow offs?
Bounds - I just bought this setup last year and have been very happy with it. I'm not sure what you are using for a primary, but here's what I did: At the time I bought the controller I also bought a 6 gallon Better Bottle for my primary. This meant that I 1) couldn't use the 6.5 stopper the thermowell came with and 2) would more than likely need a blow off. I bought a couple of solid #10 stoppers to fit the better bottle. There is plenty of room on a #10 for two holes. I drilled one hole just big enough to put the thermowell through and one big enough for a 3/8" line. I wish I could remember the diameters I drilled, but can't now. Just remember that you want a snug fit and the rubber will stretch a little, so under size it. You can always drill larger if needed, but you can't make a drilled hole smaller!
If I ever want to use the thermowell for secondary fermentation (which isn't very often), I take it out of the #10 and put it back in the original for use in a standard glass carboy. If you primary in a standard carboy, you could just drill out the airlock whole on the 6.5 stopper a tad to accommodate a blow-off hose.
If you do go with this setup, a word of wisdom I learned the hard way. Running the Johnson Controller's probe down the thermowell is great if you are using the heater - will hold it within a degree and it did a great job holding my ale @ 66 in a 58 degree basement. You just need to start off at the temperature. The FermWrap will hold, just not great at heating up. However, if you are using it for cooling in a fridge or freezer, you probably don't want to do that. What I ran into was that by the time the freezer got cold enough to affect the core temp of the fermenter, it got really cold and would end up dropping the temp 4-5 degrees before it stopped. For cooling, I now use the Johnson to control the ambient temp of the freezer and an inexpensive digital probe thermometer to run down the well to accurately measure my fermentation temps. If the fermenter gets a little warm, I adjust accordingly.
I highly advise picking this kit up. It's a great buy for the money and probably the best money I spent on my brewery. Reliably controlling my temperatures has taken away a lot of aggravation and improved the quality of my beer. It's also nice to brew what you want, when you want.