Continuous Fan Set Up (Lennox)

RLF

We have 2 forced air furnaces in our home; Lennox Model G26Q3/4-100-6 and Lennox Model G4OUH-36B-090-03. Both are about 1 yr old. and have seperate wall controls allowing for "continuous" or "auto" fan. When the fan is running in "continuous " mode the fan speed is the same as when blowing heated air. A non-techie advised me I have the ability to run the "continuous " fan mode at a slower speed (eg 500 cfm) and then when calling for heat, automatically increase the fan speed (eg 900 cfm). I am not interested in changing out the motor, and wish to have the ability to switch "off" the low-speed continuous fan but still keep the furnace on call for heat as required. It was suggested this can be accomodated at little expense,without adding much in the way of new parts.
My question: Given the make and model of each furnace can anyone tell me what parts or components would be required for each unit (I may not be able to afford doing this to both units)to run continuously at a lower speed. I understand I may a switch for each unit but neither or only one (which?) may require a relay? Any other parts/pieces?

Thanks in advance for any help you can provide.

Wayne_12

Lennox fan speeds

The G26Q34- gas furnace ignition control board has 3 electrical terminals identified as ACB Low, ACB Heat, and ACB Cool. The terminals are located in the upper left side. There are 2 additional terminals labeled M1, M2. M1 and M2 are there to store unused electrical wires from the indoor fan motor. With a 4 speed fan motor, 1 wire will be on low, one wire on heat and one wire on cool, leaving 1 wire to be parked on either M1 or M2. Doesn't matter which terminal.

Place the red wire from the indoor fan motor on the ACB low terminal. The red wire or low speed is the lowest speed available.

Determing what fan speed is required for heating or cooling is to be determined by measuring the heat rise across the heat exchanger for the heating speed or measuring the temperature drop across the evaporator coil for the cooling fan speed.

The other furnace should have simular terminals and the fan speeds are selected accordingly.

WD

RLF

Lennox- Continuous fan speed

Wayne, thanks for the response. I'm not sure if my original request for info was unclear, but both furnace units currently run on continuous fan when the option on the wall thermostat is moved to "fan-on" vs "auto". What I'm hoping to acheive is a slower continuous fan speed than that which I curently have. I wish to maintain the current fan speed for the heating cycle. Any additional ideas?

JP

Lennox Blower Speeds

As Wayne stated in the earlier post the best you can do with the blower speeds on these units is to put the low speed wire on the "low" terminal on the board. The G26 unit on low speed @ .25" of static is rated at 1210 CFM. This is as low as you will probally get this unit to go without increasing the static on the system. But even at the maxium static design of .50" the CFM is still 1100 CFM. The G40 on low speed at .25" of static is rated at 875 CFM. The only units that will allow you to have that low of a " fan on" speed are the variable speed units. As far as I know there are no upgrade kits available for these unit to retrofit in the varaible speed motors, and if they are available they would be very expensive.Hope this info helps.

John

Dale

New furnaces

They are set up to run on heating speed when set to fan On or continous. As the other post suggested go to the lowest blower setting, usually the red wire and see if the heat rise is still in the allowable area per nameplate. One problem with furnaces is that they are made for alot more AC than needed up north and since you have large inputs you may want to choke down the outlet duct word even on the lowest speed.