by Geoff » Sat Apr 09, 2011 9:09 am
I've always use a thermostatted box, for beer wort or spirits wash. I reckon a concentrated heat source has a chance of killing some yeast, don't know if it does in practice but controlling the air temp around the fermenter seems to be a better long term solution to me and is simple. Since I undertand electronics, I made a box with an electronic thermostat. It also has a temperature indicator on the outside so I can monitor.
Now, I am in Melbourne and overnight temps can drop to 8 deg in the garage. My heater is some resistors mounted on a heatsink with about 90 watts of heat available with a fan. A temperature probe monitors the temp about 50 mm from fermenter. The box is partially insulated and is about 60mm bigger than the fermenter on the sides with a flip top to access the airlock and lid. For turbo washes, the box cannot be fully insulated as it needs to be able to lose heat on the second day as you will all know the fermentation is very exothermic at this time. In practice, a plywood box with 2 or 3 sides insulated is adequate, depending on the climate.
I have an electronic thermostat I knocked up out of bits out of the junk box. Can be set from 18 to 35 degrees. The advantage is that no monitoring at all is needed. I know the temperature will stay at say 25 degrees for the entire time. This is great for beer wort or bottles too.
Another idea for a controller which I made for my father is using a central heating thermostat. Thes ehave the right range for brewing and can be had by a bulider do renos of older houses for free if you are lucky. The can control usually a low voltage load via a relay. Waterbed thermostats are good too but are mains so you need to know what you are doing around electrics.