Varying the Speed of a High-Efficiency Furnace?

[THE SCUD]

Hey CP,

With winter coming I did a few mild upgrades to my 3 year old home with an H.E. Furnace, which included a wifi-enabled thermostat (kick ass, I highly recommend it - I changed my temperature from Paris last week!) and a new filter. This got me thinking about my previous winter....

Last winter was my first with an HE furnace, I was wondering if the following is possible:

• Can you change the fan speed on an HE furnace? I know there are some variable-speed models out there, but I am unsure if mine is (I'll check when I get in from work, but I am assuming it isn't).
  
  
• If I have a 'one speed' fan in my HE furnace, does anyone know if you can retro fit a variable speed fan, or some form of fan speed controller? The jet engine roar is annoying at times (but the cheap as borscht NG bill is awesome)

[Sliver]

Yeah the fan on my HE furnace is annoyingly loud, too.

[Northendzone]

i caught an episode of this old house a month or two ago and they were putting in a furnace with a variable speed fan - i really like the idea of having warm air circulated at a low speed all the time. although i wonder if it would be effective on the second floor.

i swuppose a wi-fi enabled thermo would be kind of cool though, although i am not sure i'd ever really use it - although there is the odd time where we have gone away for a weekend and forogt to lock the thermo on 16......

[THE SCUD]

Dammit, why doesn't CP have a resident furnace guru?! I swear it's scary that a thread on belts has more replies than a furnace thread.

Maybe CP is turning into Chatelaine Place?!?!

[Draug]

Originally Posted by THE SCUD

Dammit, why doesn't CP have a resident furnace guru?! I swear it's scary that a thread on belts has more replies than a furnace thread.

Maybe CP is turning into Chatelaine Place?!?!

There is one ... EVERLAST. He's done work for me and I can highly recommend him.

http://forum.calgarypuck.com/showthread.php?t=104907

I am sure he'll reply to this thread at some point, but I'd bet anything that he is out actually working on furnaces on this fine fall afternoon.

[iamajai]

We have a variable speed Lennox (about 18 months old now). With a dual stage thermostat (Hi/Lo heat) it will provide fully variable flow and heat output. With our single state thermostat (Heat/No heat) it will ramp jump from 33% to 66% to 100% after every 15 minutes until the setpoint is reached.

You can adjust the time delay between stages through a series of DIP switches after opening the front cover.

You can also adjust the steady fan speed (which you can switch on manually to provide airflow through the house) through another set of DIP switches. I have mine set at the lowest 30% speed so it is near silent, but provides good cooling in the summer. Our ducts run through the concrete slab in ground prior to entering the rooms in our home so its a cheap cooling system in the summer.

The furnace manual, if you can find it, should have an explanation of the DIP settings.

[THE SCUD]

Originally Posted by iamajai

We have a variable speed Lennox (about 18 months old now). With a dual stage thermostat (Hi/Lo heat) it will provide fully variable flow and heat output. With our single state thermostat (Heat/No heat) it will ramp jump from 33% to 66% to 100% after every 15 minutes until the setpoint is reached.

You can adjust the time delay between stages through a series of DIP switches after opening the front cover.

You can also adjust the steady fan speed (which you can switch on manually to provide airflow through the house) through another set of DIP switches. I have mine set at the lowest 30% speed so it is near silent, but provides good cooling in the summer. Our ducts run through the concrete slab in ground prior to entering the rooms in our home so its a cheap cooling system in the summer.

The furnace manual, if you can find it, should have an explanation of the DIP settings.

Thanks! I noticed a bunch of dip switches when I took off my furnace cover, so I am hopeful I can adjust the steady-state speed. When I hooked up the wifi thermostat it appeared that I only have a 1 stage (non variable) HE furnace, but I will search for a model number and confirm. Either way, even being able to reduce the fan speed would rock.

[THE SCUD]

Well I found my model number, googled it and came across the instructions on how to modify the fanspeed - it involved wires on heat, cool and several parked ones, so you just put the differnet color on heat that corresponded to the speed you wanted.

IE: black is high, red is low, yelow med-hi, brown med-lo.

However, it was already on med-lo, so I put it to high and there is a lot more volume coming out of the vents, so I'll try that for the winter and see how it goes, but it certainly didn't help the noise, I guess its more reverb in the vents from the HE furnace.

Is there any way to quiet down the reverb (vent noise) from an HE furnace ?

[sclitheroe]

Originally Posted by THE SCUD

Is there any way to quiet down the reverb (vent noise) from an HE furnace ?

Move to Ranchlands so the humming drowns it out?

[jeffh]

A few ways you can use to quiet it down are:

1. Insulate all the duct mains with foil back insulation and use foil tape to hold it on. A practical method and good results, if your main ducts aren't covered up by drywall.
2. Have canvas connections installed close to the furnace on supply and return plenum ducts. This will mechanically isolate your furnace from the rest of the ductwork in regards to vibrations and some noise.
3. Slow down your noise-making-fan/blower...(sounds like you already tried that)...also keep in mind your furnace will be running longer to reach the set-point.

There are other methods, but these are the more practical ones.

[sclitheroe]

Originally Posted by jeffh

A few ways you can use to quiet it down are:

2. Have canvas connections installed close to the furnace on supply and return plenum ducts. This will mechanically isolate your furnace from the rest of the ductwork in regards to vibrations and some noise.

That's a really neat idea. Are these commonly available?

[jeffh]

No, its completely custom, and something you would probably want a pro to do. I recommend having it done when you have your furnace replaced, as it also makes the new install easier. It isn't difficult to install afterwards either but you need about 8" of duct space to install it...so if you have an A/C coil as well, there may not be enough room for it, at least not on the main supply plenum.

Duct design and incorporating radius fittings reduce sound too. This is something that most return ducts tying into your furnace lack.

Also a heavy duty rubber mat/tile(like in hockey dressing rooms) installed under your furnace would be another way to reduce vibration noises. Obviously you would want to do this at time of replacement.