lennox adjustments

[nedjinski]

we have an older lennox forced air heating furnace.

the control box has a dial with 2 pointers - one pointing at a high temperature and the other at a low temperature.

when we moved in here the controller was set to: 200 / 90

I assume this is the temperature that the burner heats up to and the temperature that the fan turns off at?

I want to set the temps for the maximum efficiency and least gas useage.

what do you recommend as the ideal settings?

[coolwhip]

Dont fiddle with that, it is a safty control.

[t527ed]

leave them where they are. one is fan off, other is high limit.

[Toolpusher]

To get max eff
You may want to upgrade to a new 90% or 80% with variable speed drive.
You'll be glad you did.

[nedjinski]

thanks toolpusher -

what does the 80 / 90 refer to?

and on my original control box - does the 190 limit temp refer to the air temp before the fan goes on, or the constant air temp while it's running, or the temp of the burner, etc?
and the lower number, 90 in this case, does that refer to the temp at which the fan goes off or on, etc?

[comfortdoc]

190 is the high limit. If the heat exchanger reaches this temp the burners are shut off. Sounds a bit high to me as it is.

The 90 is the fan off setting.

Have the heater inspected by an experienced service tech. He will be able to advise on the settings based on furnace model and operation.

[mark beiser]

Yes, the 200 is the limit temperature. If the limit control ever gets to 200º, it will turn the gas valve off and attempt to run the blower until the limit resets.

The 90 is the temperature that the control turns the fan off after a call for heat ends.

From your desctription, and the fact that it is an old Lennox furnace, the control is a Cam-Stat brand fan/limit control, I bet it is 7" insertion too. Since it only has 2 dials, it is a timed on control with 6 wires going to it, so there isn't a dial for the fan on temperature.

As others have said, don't mess with it.

If a technician ever has to replace it, don't be to suprised if the replacement looks totally different. While Lennox primarily used Cam-Stat fan/limit controls, the furnaces also have mounting holes for a Honeywell control in the same spot. The important thing is that the replacement be a 6 wire timed on type with about the same insertion depth.