Lennox CBX32MV-060 Fan Running At Full Speed During Heating Cycles

[super dave T]

Good day. I have a Lennox CBX32MV-060 electric furnace with a five bank set of heating elements and no heat pump and no air conditioner.
Neither a discharge air sensor or outside air sensor were installed.
A Lennox iComfort S30 is installed for the thermostat.
During all heating cycles the fan runs at full speed, (2005cfm) regardless of the number of heating elements that are engaged. Most of the time the furnace runs with 2 elements but occasionally it will engage three, or four. Rarely 5 unless the house is very cold as a result of the furnace being shut down for a period of time.
The jumper between W1 and W2 have been removed and the control board has all of the jumpers at their factory default position.
As this is suppose to be a variable speed furnace, the table I've attached below tells me that the fan cfm's should reflect the number of heating elements engaged but such is not the case. 2005cfm during every heating cycle regardless of how many elements are on.

Thanks for having a read and I'd appreciate your input on this as listening to jet a jet engine taking off for 30 minute periods has gotten really old these last 2 months...lol.

[Admin]

The air handler usually ships with the heating speed set to HIGH.  Using jumpers you can reduce this to MED HIGH, MED LOW or LOW.  There is also a jumper to reduce the airflow by 10%.

Keep in mind the table you posted does not reflect the number of heating elements.  The 1, 2, 3, 4 refers to the heating speeds, HIGH, MED HIGH, MED LOW, LOW.

You could try adjusting the air handler jumpers I circled in red, to see if that changes the heating speed.

[super dave T]

Good morning Admin. Thanks for the suggestion and the clarification on the table. I changed the jumper to the lowest of the heat speeds with no change. But if it had worked and lowered the speed, what do you think it is that is built into the system that would tell the blower to operate in variable speed mode? As most of the time the furnace engages 2 elements,(but I've observed as many as 5 with the same number of cfm's), it doesn't make sense to have 2005cfms blowing over 2 heating coils.

[Admin]

What is the Heating Airflow Control Type set to in the S30 settings?  Fixed CFM or Fixed DAT?

[super dave T]

Good morning Admin. Well this was a bit of an exercise. I poured through the various pages of the manual as well as the various screens to look for the setting and could not find anything regarding a setting for Heating Airflow Control. That said, I was only looking under the Air Handler section of the manual as this is what my furnace is classified as. Then I happened to continue further and found the the Heating Airflow Control is in fact listed under the Furnace parameters of the s30 manual. But there is no reference listing on any of the s30 screens that mentions the HAC.
Is it possible that because the thermostat is not detecting a DAT that it is not giving me the option between fixed cfm or DAT and therefore fixed cfm is default?

I have included pics of the entire page of the "About" section for the handler for your reference.

Thanks, dave

[super dave T]

oh, and my apologies. I forgot to mention in my last post that I configured the unit size to reflect the air handler model number. that resulted in the cfm being lowered to 1705. Since then, the cfm's have been consistently 1705 with no variation regardless of the number of heating elements engaged.

[Admin]

Is this a communicating system with the air handler and thermostat wired to i-, i+, R and C?

It should auto detect the equipment.  It looks like it auto detected the 5 elements and lists 5 heating stages.

Did you leave the jumper set to LOW after you entered the AH model number?  That could be why you are running on LOW 1705 CFM instead of HIGH 2005 CFM.  You could enable the -10% jumper to reduce to 1560 CFM.  Depending on how many kW the elements are you need at least 70 CFM per kW.  So if you had 5x 5kW elements a CFM of 1750 would be good.

The Heating Airflow Control Type option is only available with the furnace selection apparently, and not with air handlers.  Sorry, I've never setup and air handler with electric heat only.

I attached a pic of the Electric Heating Airflow section, under Air Handler parameters in the manual.  I'm not really sure what it means by "incremental adjustment of 5 CFM".  It seems to imply the heating speeds would vary with the electric heat stages, but maybe that's not the case. 

You can switch the Electric Heat Control Mode from Standard to EvenHeat but that requires the installation of a DAT.  I believe it only supports up to 4 electric heat stages but that may be what is needed to see more controlled blower operation.

I would give Lennox a call at 1-800-453-6669 to make sure.  Press 2 for Technical Support.  They should be able to explain if the blower will vary it's speed with each stage of electric heating.