Honeywell Fan Control Help Needed

I bought a Honeywell L4064 B 1541 combination fan and limit control but it didn't come with instructions. How do I hook this thing up to my furnace's circuit board to run the fan and also how do I hook the limit to my boilers Honeywell L8124 aquastat?

Try these guys, very helpful:

https://arnoldservice.com/fan_blower_controls.htm



Edit: Forgot to add the Honeywell site:

https://customer.honeywell.com/Business/Cultures/ ... efault.htm

The L4064B is a dual contact control. One contact closes at the fan on temperature set point and opens at the fan off temperature set point. The second contact is normally closed and opens when the high limit set point (factory set at 200 deg F).

These contacts are wired in series with various circuits in the aquastat depending on what you are trying to do. For example it could control the circulating pump, gas fuel valve, oil burner ignition, coal combustion blower, etc. What are you trying to do?

e.alleg wrote:how do I hook the limit to my boilers Honeywell L8124 aquastat?

The high temp limit? I think I have the wiring diagram for that somewhere. Mine runs with the same controls.

Thanks for the Honeywell link, I was able to get the instruction sheet. I just hooked up the fan control side, after thinking about it I don't think the high limit in the duct is necessary as the boiler has a high limit cutoff based on water temp. If I'm wrong please let me know, but I ran it today and the duct never got close to the 220 degree high limit, it ran about 150-160 degrees with the water temp at ~200 degrees. Just for argument sake, at what temperature will the metal ductwork set the floor joists on fire?

I agree, you don't need to use the duct control over temperature limit switch. Your duct work would have to get awful hot to get the joists on fire. Most building lumber has ignition temperatures greater than 200 deg C (392 deg F). Actual ignition temperature varies greatly with the high temperature exposure time. Don't worry about it.

Yanche wrote:Most building lumber has ignition temperatures greater than 200 deg C (392 deg F). Actual ignition temperature varies greatly with the high temperature exposure time. Don't worry about it.

Yanche is right on here. I will note that wood near a stovepipe exposed to high temperatures for a long time will dry the wood out considerably, this can reduce its ignition temperature significantly. It can cut ignition temps in half depending on exposure time, temperature and species. Following the code greatly reduces this risk.

For the record, anyone looking to hook up a coal boiler to an existing forced air furnace, this is the fan control (Honeywell L4064) you need. I had a hard time figuring out what to do to make the fan run properly. The problem is that my forced air furnace is a newer model which uses a timer instead of a thermostatic switch to run the fan. The sequence is as follows: thermostat calls for heat, the exhaust fan comes on, then the burner lights. 90 seconds later the fan comes on and runs until the thermostat on the wall is satisfied OR one of the safety switches opens. Once the house is up to temp the burner shuts off and the fan continues to blow for 120 seconds to expel and heat left in the plenum. That is what makes it 90% efficient. I have 2 thermostats now, one turns on the coal boiler and starts the circulator pump, and once the plenum gets above 140 degrees the fan comes on and warms the rooms. Once the thermostat is satisfied the stoker shuts down but the fan keeps going until the plenum is below 100 degrees. Cold air never comes out of the ducts. During this weather where it's 30 at night and 60 during the day I leave gate vales to the heat exchanger open so the heat exchanger stays hot and gravity flow warms the house without noticeably drawing down the boiler water temp. I put an on/off switch on the fan line to prevent the fan from coming on when doing this, otherwise the fan will run and cause the boiler to cool down and waste coal.