Furnace fan speed control

[2oldman]

Atwood motor. Just had it replaced and boy it's loud and seems to be running way too fast.

Assuming there's no speed control on the motor, I can put one on assuming I find the correct wires. Would really be nice to have variable speed on a furnace fan.

Anyone done this?

[landyacht318]

If using a PWM motor speed controller on a fan motor, seek one with 21kHZ or higher, as the windings will whine annoyingly at reduced speeds, depending on the age of your ears.

It's amazing how much quieter a well balanced fan impeller is.
I use a free accellerometer app on my phone, and some trial and error adding small weights, to greatly improve fan noise. Some fans have gone from an intolerable drone, to 'is it even on?'

[2oldman]

Housted wrote:
I did this several years ago and love it.

Thanks. I used a similar one for my range hood exhaust fan and love it. That thing ran so fast it almost sucked the flame out.

Likely need a bigger one for this motor.

[dougrainer]

If it was running too fast, it would not light. Doug

If you want to spend the money and you MUST use the Wall tstat for this model.

https://www.amazon.com/Atwood-38542-2-Stage-Excalibur-Thermostat/dp/B00CLSWD6S/ref=cm_cr_arp_d_produ...

[2oldman]

It's not the wrong motor.

[midnightsadie]

#1 could be the wrong motor#2 could be its right and the old one was wrong.

[2oldman]

This is the 2nd furnace in the bathroom, not the main one. It's never on unless I need the room pre-heated for my shower.

[dougrainer]

The Fan SPEED on a RV furnace dictates a lot more than just blowing air out the floor ducts
1. The Fan RPM is what closes the sail switch to ignite the furnace. Too slow and it will not light, or hunt back and forth
2. The Fan RPM is designed to bring the correct amount of air IN to the burner chamber to correctly mix LP and air to get the correct flame
3. The Fan speed also dictates how large an area the furnace will heat Doug

[Gdetrailer]

Wow..

Looks like a potential Darwin Award candidate.

Take the extra air flow and noise and live with it, your furnace will thank you, heck you might even wakeup alive and not on fire..

Seriously, reducing the motor speed on these furnaces is asking for trouble, they are highly compact and depend on a certain minimum amount of airflow to keep them from igniting things like the floor and walls.

So, unless you manage to dial in and nail the exact minimum airflow (which is not only on the inside but the outside combustion side) you are taking some big chances even with maintaining enough flow to keep the sail switch happy.

Perhaps you bought the wrong motor?

They DO make different motors for different BTU furnaces that run different RPMS.. I would suggest attempting to find the correct exact replacement before kludging your own work around fix.

[beemerphile1]

It would be great, but, the fan has to move enough air to engage the sail switch. I wouldn't put a large effort or dollars into it in case it doesn't work. Keep us apprised if you do make the attempt.

[Housted]

I did this several years ago and love it.
I used this one --> https://smile.amazon.com/dp/B07B4B2X35/ref=dp_prsubs_1

Works great, but really shows the change in speed with voltage change.
Sometimes must run faster than we like to keep the sail switch engaged.

Would do it again. 🙂

Housted