Thermowell Users, Please Weigh In!!

Over the past 6 months I have been brewing on my rig and finding problems to fix. Recently I re-located my thermowells from a T fitting on the outlet of the Hot Liquor Tank and Mash Tun. I was having problems on the MT with grain getting stuck due to such restricted flow from the thermowell. I moved them to the inlet of the pumps and lost the flow problem. Last brewday went flawless as far as that was concerned. The new problem I encountered was that my temprature reading was WAY off, ranging from 6-10 degrees. I think it had a lot to do with the cold weather but I want a system that is accurate in both summer and winter. Fortunately I still had my thermometers installed and used those along with a digital. The next step will be to put a heat shielded thermowell into the side wall of the HLT and MT. I know I want a heatshielded thermowell, but I am unsure of how deep the thermowell needs to go to get a truly accurate reading?

Brewers that have this type of setup with the thermowell inside the HLT and MT, how accurate is it? Also, what size thermowell did you use? I would also like to hear your opinion of this method rather than an in-line temperature probe. Thanks!

I made a DIY thermowell in my MLT out of thin copper tubing, compression fitting, and a couple other plumbing parts. The well is longer than it needs to be because I wanted to make sure that I didn't have to re-do it if I ever got a different thermometer to stick into it.

The thermometer I use has a 4' probe, but I would estimate that only 2" or 2.5" of the probe is actually "inside" of the MLT. The other 1.5" to 2" is resting in the hardware on the outside or within the wall of the MLT.

Depending on how cold the ambient temp is, I get varying results for my readings. When I built the thing and tested it in the house (70*F), the reading was very accurate. I checked the temp in the thermowell and then move the probe so that it was actually poked into the water in the MLT and checked it there. The difference I saw was only about 0.2*F (the thermowell reading was a little low).

However, when I brew in the garage at this time of year and the temp is down in the 30's or 40's, the thing can read about 1.5*F low.

If I had a longer probe so that more of it was projecting into the MLT, then I would suspect that the reading would be better, but I can't say for certain because I just don't have a longer probe to do the test with.