Heating problem.....

Im running a rack with 5 shevles and 3 of the shevles are on 1 thermostat..the therm has one sensor on it ...so im putting the sensor in the middle shelf...but the other shevles are running higher...they are have 3 in tape....what can i do....

If I am understanding you your rack is hotter at the top spaces and cooler on the bottom? This is typical, heat rises :rolleyes:. Is the rack in a regulated room (is the room temp set to 80º?) In a regulated system the gain often isn't really large and a balance can be found to keep things reasonable (Ie, 88-89 at the bottom and 91-2 at the top) In cool conditions the shift is often larger, sometimes lots larger the bottom might be mid 80s (83-5) and the top could be in the 90-3. This is due to heat loss.

If this is the case, I am guessing here, the simple solution is to heat the room to slow the heat loss. If this is not possible or reasonable you could try to insulate the rack to help hold the heat and slow the loss. The sides and possible the bottom from the floor if it is cool. Also you may find that the middle spaces (you are using 3 or 5 right) will be closer than the bottom and top slots.

I have a rack in a cool room and I have insulated the rack and had to add secondary heat for control of the cool end. I am running 3 probes to the rack the hot side on one the top 2 spaces cool sides on a second and the bottom 3 cool sides on a third. It is working quite well for me but isn't a cheap option or very easy, in MY case it is much easier than trying to heat the room to 80º as the basic oil heater does not have enough power to do so as the room is quite cool and quite draughty.

If you can describe you situation I may be able to offer more specific ideas.

What i meant was i feel that the heat tape is not turning off on the 2 other shevles without the probe....if i have all 3 plugged in to the same unit i thought that when the thermostat hits its target on the one with the probe they should all turn off....But they might be... now you got me thinking that it might be what your saying...i have to look into it tomorrow... thanks so much for the help..Richie Boo