Originally Posted by KeepItSimpleStupid
I only use manufacturers websites for information. Most mfgrs have installation manuals for their tstats and those are where you will find how to set them up correctly. Honeywell has very good information, but their search function is absolutely pathetic. Don't search for a complete part number! And keep everything you find on your computer so you don't have to go through the agony again.
I don't believe that I've ever seen a fossil fuel tstat that drops W1 when a higher number call comes in, they are called in addition (see next paragraph for exception). The functionality that I suggested for the OP required that when W2 (or W3) is satisfied, they will drop out and leave the earlier calls in. Of course if there is any stage not satisfied, the fan will be on, which I believe is what he wants.
A heat pump tstat may disable the compressor (1st stage heat) on a call for emergency heat. Depends on how it is configured, but even that will still have the fan called.
That RobertShaw that you mentioned is a NICE tstat. Expensive too. And yes, they don't give you the max differential in the manual. I think you got the sell sheet. Here is the manual from the manufacturer. http://www.icca.invensys.com/manuals...w/110-1069.pdf
I have one on my parts shelf if you really need to know that information.
I wish the OP would come back and give more detail on his requirements. If he wants the fan to be on all the time the woodstove is hot, and when it is cold, then the fan will run only when the fossil fuel furnace is called, then my idea won't work well. He will need two tstats for that the scenario, the one to call the fan for the woodstove would have to be set for cooling, and then he probably would need relay isolation for the two. The question was vague enough that I almost didn't jump in. Now I have spent a lot of bandwidth just about thermostats.