> Bob, I am very happy with the incubators that I have build from salvaged
> upright freezers.  Use a salvaged mercury wall thermostat, a simple Radio
> Shack low-voltage relay, a thrift store warming tray as a heat source, and 
> a
> salvaged computer fan.  Cheap and extremely accurate.

A bar fridge would work well, too. Maybe even those coolers that warm or 
cool.

The thing is that you do not want to have too strong an element that heats 
up fast then overshoots from inertia.

The ideal is to have just enough heater power that it runs about half the 
time.  That way, the swings are minimal.  Just because the thermostat cuts 
off the power does not mean that some heaters will not still give off heat. 
Personally, I used rough service light bulbs painted black, two in fact to 
ensure against failure of one.

All this is assuming the room where you keep the incubator is stable at a 
constant temperature and does not get over 90 degrees.

If it isn't, that will affect your regulation of the incubator.

For example, if the incubator is in an outside shed that goes form freezing 
to 110 degrees, you will have big problems.

For one thing, heating the incubator will be only half your problem, 
obviously.  Keeping from over heating will be a bigger problem.

Get a high/low recording thermometer and run the incubator a while before 
you commit cells to it.  If it ranges more than a degree total after 
stabilizing, IMO, it won't do. 

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