Fan Control Based On Thermostat Temperature


New Member
Hello All,

I have read many posts here, thanks very much for all the great tips!

Before buying the last of the needed components I wanted to make sure this would function as expected.


I am going to add a RCS TR-60 thermostat to my Elk M1, this would be placed on the main floor of the home. On the top floor of the home I am going to install an Elk remote temperature probe. In addition to this an Elk rely would be used to connect directly to the 24 volt switch block of the furnaces forced air blower (fan).

Desired function:

The top floor of my mostly open concept 2600 square ft. becomes either hotter or colder (summer/winter) then the main floor throughout the day. I would like to continue to control the house temperature on the main floor, but would like the furnace fan to run whenever the top floor temperature deviates (say 2 degrees above or below) from the main floor thermostat temperature set point.


From everything that I have read this seems very do able. Can anyone offer any tips or caution with this type of implementation?

Thanks, Mike


Senior Member
It's been my experience that the fan alone isn't enough to equalize the temperature differences.

If you want to have a single HVAC system manage 2 floors, get a zoned system. I swapped out a builder's 2-zone system literally just today with an RCS system for Elk control... In my case, I have a newer home with a 5-ton HVAC system managing a 4,000sq ft house using a 2-zone system and it works great. In contrast, I used to have a 2400 sq ft house with a single HVAC not-zoned... the fan just didn't equalize anything - I found myself in the attic manually adjusting the dampers every season.

I'm not sure what you mean by "concept" - to me that means it's not built yet... if that's the case, fix it now before it's too late - it'll cost at least $5K to fix it later.

Kevin L

Active Member
I agree 100% with Work2Play. I have a 3700 sq ft home in SW Florida. Heat's not much of a concern, but cooling definitely is. Downstairs we have a split plan with 2600'. I have a Trane 2-stage (2 separate compressors in one unit) handling the first floor, with a 3-zone Honeywell EnviraZone system. One zone is the left side of the home that has a bedroom, bath, and an office; another zone handles the open family room, kitchen, dining room, and living room. The third zone handles the guest suite. This setup lets me close off the guest suite and set the stat much higher when not in use. I couldn't be more pleased with how great the zoning works.

Upstairs with have an 1100' master suite. We have a separate smaller Trane a/c unit to handle this. I do not have zoning up there.

I have yet to tie the stats into my Elk/Homeseer automation. I currently have four of these, one for each zone: http://customer.hone...spx/TH9421C1004. I've been a little hesitant to tie them in since they work so well and I'm concernced about how the automation will work with the zoning. I have seen some reports of a z-wave version of this stat on the way.

Good luck,


New Member
Thanks for replies and information!

The solutions that you guys are using are really what should be used.

My home is new and came with a very basic furnace and heat pump system (builder special). It's all new and very cheap to run. I know that the best solution would be to rip this out and put in a higher quality system that has variable speed fan control along with zone control. I would love to do a major upgrade, but just can't at this time.

I am actually able to achieve a very good result by just manually turning on the fan and letting it run for about 20 minutes and then turning it off.


During the cold season the main floor thermostat is set to say 72 degF. After the set point is reached the whole house feels pretty good. Over the next hour or two the top floor starts to cool and as expected the the main floor holds it temperature longer or even increases for a time due to lights and various activities. If I walk over to thermostat and turn on the fan all of the cool upstairs air is moved down and mixed, which may or may not cause the furnace to trip on. After about 20 -30 minutes I am all good for another hour or two.

The house has good air flow. I describe the home layout as "open concept". There are fewer doors and walls. Defining fewer is a little difficult. The stairs going to the top floor is quite large and open. From the top you can see a lot of the main floor.

As for the Elk system in terms of reading the upstairs temperature and the main floor thermostat set point can I get Elk rules to handle fan control via an Elk relay? I have test the relay manually and it works as expected.

I am just worried that I will spend all this money on a integrating thermostat and temperature probe just to discover that an Elk rule is not able to do what I need.

Thanks again,



Senior Member
If you are able to control where the air returns are sucking and where the air ducts are blowing you will have more success. For example, if the return air dampers on the second floor were open and the air ducts on the first floor are open it will draw the warmer upstairs air in and deposit it on the first floor, mixing the air and balancing temp. This works best in open floor plans. If you have closed off areas it presents problems with air trying to force around doors and stuff.

If you already have a main trunk that splits to the first and second floor installing a automated powered damper isn't very hard. Same with the air return. But if you aren't already ducted like this, a retrofit is hard.


Tcat, If you can achieve a very good result by just running the fan every 20 minutes, the simplest solution would be to replace the Tstat with a HAI RC1000 (or similar). It has a circulate function that will kick on the fan at intervals even when heating/cooling isn't desired. No need to write a rule and you get to adjust your temps from your cellphone with the right add ons..


New Member
I had an extra relay so I just wired it in as a test. I actually do not have the thermostat, Elk thermostat interface, and remote temperature probe yet. So, I am not completely sure of the control possibilities or any limitations that the Elk rules may present or how they will relate to the hardware. Its just a little idea in my head right now.

The advice that I have been given above is good, but is just too cost prohibitive for me at this time. I think I am just going to buy the items and give it a shot. My main concern was in dealing with the Elk rules and wether or not they would work the way I need them to.


New Member
TheEther, just missed your post.

I did briefly look at the thermostat you suggested, nice product. Just having the thermostat run a fan schedule really might be the way to go. That was going to be my plan B if the Elk control part did not work as expected.


Senior Member
If you have a controllable thermostat and a temperature sensor, you should be able to compare values and turn the fan on and off no problem with Elk rules.