Putting a filter in my cold air trunk?

BowDown · 09-17-2009, 03:31 PM

I have an older Lennox natural gas forced air furnace in my house. It has the hammock style filter cage. My cold air trunk comes off the left side of the furnace and that side of the cage is always filthy.. but the rest of the filter is clean. Seems like a big waste of a large filter. I was thinking about modifying the cold air trunk to use one of the mainstream off the shelf filters.

How do I size the correct thickness of filter? Obviously I can't install a filter larger than the trunk.. so thickness is my only variable.

Also do they make kits to do this? I have no problem working with tin.. just want to make this look as pro as possible.

Other than that.. the furnace still works great.

That's the only pic I have of my furnace.

hvaclover · 09-17-2009, 04:50 PM

yuri · 09-17-2009, 07:24 PM

If you have a damper in the venting right where it attaches to the furnace that is the bimetal autoflo type I would get rid of it ASAP. When they fail they spill fumes into your house. The metal inside hardens up/slows down and they are deadly and no longer sold.

BowDown · 09-17-2009, 09:47 PM

Quote:

Originally Posted by yuri

If you have a damper in the venting right where it attaches to the furnace that is the bimetal autoflo type I would get rid of it ASAP. When they fail they spill fumes into your house. The metal inside hardens up/slows down and they are deadly and no longer sold.

Good to know. Thank you. I will swap that out! Do you want a better picture to identify it? What do you swap it out with a straight section?

As for the other guy... is that a piece I can buy at a heating store?

BowDown · 09-17-2009, 09:52 PM

I checked it out just now and it looks fairly new and the actuator moves freely... still swap it out?

yuri · 09-17-2009, 09:53 PM

Does it have a motor to drive it open?
The manual heat actuated bi-metal ones are very unsafe. In Canada we had some sold/made by Autoflo and I am sure other companies made them. Get RID of it no matter what!! Use a straight piece of pipe. They had a legal disclaimer that it needed checking once a year, ya right, still failed anyway when you least expected it. You have no space between your return duct and the furnace (offset) so you cannot install a 1" filter rack. Those hammock filters are not expensive so I would keep using it.

BowDown · 09-17-2009, 09:56 PM

Quote:

Originally Posted by yuri

In Canada we had some sold/made by Autoflo and I am sure other companies made them. Get RID of it no matter what!! Use a straight piece of pipe. They had a legal disclaimer that it needed checking once a year, ya right, still failed anyway when you least expected it. You have no space between your return duct and the furnace (offset) so you cannot install a 1" filter rack. Those hammock filters are not expensive so I would keep using it.

Thanks for the heads up. Ya I would have to replace the last section of cold air trunk in order to move the cold air away from the furnace... prbly not worth it.

BowDown · 09-18-2009, 07:20 AM

The actuator is manual now... but it looks like it could be motor controlled. There's a mounting flange with 2 screw holes where you could mount something electronic.

**beenthere** · 09-18-2009, 12:16 PM

The side where the air enters from. Will always get the dirtiest.