DIY Home Improvement, Remodeling & Repair Forum

DIY Home Improvement, Remodeling & Repair Forum (
-   HVAC (
-   -   New Programmable thermostat, how to wire the fan for manual control? (

mibson 01-16-2010 11:21 AM

New Programmable thermostat, how to wire the fan for manual control?
I recently installed a programmable “Rona” Thermostat, its working great. There were only two wires to hook up so the furnace fan cannot be controlled from the thermostat.

My furnace has a “master” switch that shuts down the heat and fan. There is also a small switch inside the furnace close to the furnace fan, which I now have “on” so that the furnace fan is running 24hrs.
I would like to run wire(s) so that I can control my furnace fan from the thermostat.

How can I do this?

Note: the programmable “Rona” Thermostat instructions suggest only one more wire is required. Where would I attach, detach, or solder wires to allow me to run one wire for this purpose?

Note 2: I don’t have any electrical experience, but I’m pretty good and figuring things out and not scared to learn.
Thanks for anyone who can offer help, I can post pictures if that helps.

GregC 01-17-2010 06:50 AM

Programable thermostat
Hello, I dont want to burst your bubble but, programable thermostats are another scam which are designed by the heating & cooling manufactures. I have been a Mechanical Contractor & General Contractor for over 30 yrs now and I am not selling you anything other then the truth. Programable thermostats sound great but think about it, when they lower your heat or cooling to a much lower temperature it take so much more effort and energy to bring you desired temperature back to where you need it. They work the unit harder and longer to get back where you need it. Research has shown, by keeping your thermostat at your desired tempeture it takes less energy and strain off your HVAC system to recover. Hope this makes sense. EXAMPLE: Working the HVAC system from 60 degrees back up to 70 degrees works the unit harder and longer than if it went from 69 degrees back upto 70. If you are gone out of the home for some time, just lower thermostat for that period of time. but each and every day will cost you so much more later down the road with both energy and repair bills. Good Luck ;)GregC

mibson 01-17-2010 12:23 PM

I do understand what you are saying. However what you said does not take into account the flux of heat from the house, windows, etc, especially when, like I do, have very large windows due to cathedraled ceilings.

The heat flux, if the house is at 15 C compared to 21C when you are not home for 10hrs or more, is very significant. I dont like to disagree with you when you clearly have more experience, however I do disagree. There is also research to disagree with what you are saying. If you are just considering the extra load on the furnace and repair costs of the furnance, I do agree, but if you consider the difference between the outside and inside of the house temperatures, and the cost of gas used - I disagree. A factor here is that I live in Northern Canada and the difference between the outside and inside temperature can be as much as 60 degrees. Also, if I manually turn the termostat down when going to work(or sleep) and them manually turn it back on, what is the difference between that and having a programable thermostat do that for me?

I do still want to wire the fan so I can turn it on or off at the thermostat(programable or not). I use a standalone wood burning stove to supply at least 50% of my heat, and this causes my loft and upstairs to get very hot while the basement is cold. If I can turn the furnace fan on and off when I want to, I can make the house temperature more even.

travelover 01-17-2010 12:55 PM


I'm sure GregC knows more about furnaces than I ever will, but he is wrong about programmable thermostats not saving money. It is a simple thermodynamics calculation.

But back to your problem, I'd suggest that you see if you can get a manual for your furnace either from the manufacturer or you may find one on the web. This will show the wiring.

As an alternative find a manual for a similar furnace, as the basic logic will be the same. There is also a lot of generic information on the web re wiring conventions.

Thermostat Wiring Colors - Thermostats Wire - Installation Basics

GregC 01-17-2010 01:21 PM

Programable thermostat
Hello, This is why we call it "our opinion" but basic physics shows that flipping a light switch and the surge of electric is what blows a light bulb out 99% of the time, unless the bulb is old for some time. So leaving that light on for an hour or two saves in the long run. Running your car for 5 minutes use less gas than what it were to cost repairing parts due to turning it on and off 5 times in those 5 minutes. Same goes with your furnace, short cycles apply less wear and tear on long "catch up" cycles trying to gain 10 degrees instead of 1 or 2 degrees. If your house is well insulated it will not loose a total of 10 degrees in a cold day. (I live in Wisconsin and it has been an average of 20 degrees here now. My gas hot air furnace cycles on/off 8-10 times in 24 hrs set at a constant 68 degrees.)I have seen this, studied this and worked with Carrier, Tirane, Lennox, American Standard and several others for over 30 years to know, not just reading this out of a book or online. I said, this is just an opinion and take it as you may. You mentioned your cathedral ceilings, vaults etc. Problem is and I can almost promise you that you do not have "High" return air grills up in those vaults or ceilings. This is the key to getting the air back to floor level which keeps the air temperature at you living space level. Oh, and btw, Almost all thermostats have an Auto/Manual fan switch. Good luck, keep reading the books. :rolleyes:GregC

mibson 01-17-2010 02:59 PM

I agree with what you have said GregC. But wiring my furnace fan is what I need to do. I dont not have air intakes up in the cathedraled part, you are right. But If I use the ceiling fan on low, and turn the furnace fan on for a hour while I use my wood buring stove. The house temp is very even.

Thanks travelover,

I will do what you suggest, I just thought it would be very similar for most furnances that are about the same age, perhaps not.

I get the furnace manual and go from there.

cheers Greg and travelover!

GregC 01-17-2010 03:29 PM

A little trick for you
Hello again, here is a little trick to help with your situation. Since you are using a wood burning stove, yes all that added heat is definitely rising way above you living space. With cathedral/vault ceilings here is what to do. Use a room thermometer in low level, place one in top loft /ceiling area, monitor for a few days to get a good ready. Now lower your thermostat to your desired living area temperature and back it down by the difference in the top room thermometer( 5, 10 degrees etc) now turn on the MANUAL FAN switch on the thermostat, this should run fan full time with out kicking in any heat. This should draw hot air from up high down and then circulate back through furnace and blow it out registers. You may have to tinker abit but this works. What this does is by using the low return air register/grills it should bring down all that hot air above and recirculate it creating one big loop. Hope you understand, hard to explain but it will work since you only have low feeds and low returns. Yes the ceiling fans help but this will work along with that because using your furnace fan draws much more force. Try this and you should see an increase in room tempetature at the thermostat.
Good luck, ;) GregC

All times are GMT -6. The time now is 11:14 PM.