Jason96x

My wife and I just purchased a home built in 1900. It has two separate HVAC systems, with a package unit downstairs, and a traditional compressor/furnace combo in the upper. Most of the windows are in need of replacement as they allow quite the draft. Also, the original hardwoods are not insulated underneath the house. Everything aside, my problem lies with the package unit downstairs. With the unit turned on there is very little heat coming out of the 2 or 3 vents closest to the unit, and no heat or anything coming out of the vent further away. Upon inspection of the unit, I found what appeared to be a fresh air intake hastily screwed to the unit. There was quite a suction coming from the opening where the panel should have been. I replaced the panel that was meant to go there, which I hoped would allow the air to circulate through the house, as it should. Still, after this, no luck. I’ve been under the house and checked the ductwork to find the same thing as in the house, no air flow. My thoughts on the matter are, if the return side has such a large amount of suction, the supply side MUST be putting air out as well, so why no air through the duct?

nealtw

Air flow is measered per sq. inch. Intake may feel good but if you divide it up for all the vents it will go down. Perhaps this is an old problem that other people have tried to fix. See if you can find model and ratings on it.

kok328

I thought air flow was measured by CFM not per sq. inch.

paul52446m

We normally use a large fresh air intake on a commercial job. Maybe some one put this fresh air on for summer use to bring out side air into the house. In a old house like you have you don't want to bring outside air in.
It depends on whether your fresh air has electric or manual dampers.
You might have a slide in damper in the return air so the unit would take in all outside air. Are the return air in the house opened up? you need to take the doors off the unit and look down the return air to see if it is all open. Some where they might have that return plugged off. Make sure you don't have a plugged filter in the unit. Paul

nealtw

Inches -- feet
the point I was making if intake is the same size as output the wind will feel the same on both sides. When you divide the output into several heat registers it will be less. I think Paul has the idea.

paul52446m

[QUOTE=nealtw;52854]Inches -- feet
the point I was making if intake is the same size as output the wind will feel the same on both sides. When you divide the output into several heat registers it will be less. I think Paul has the idea.[/QUOT

A furnace blower is like a water pump, its a lot harder to pull water up but the pump will build up pressure so you can push is a long way.
A blower can build up good static pressure to push air but has trouble pulling air, So your return needs to be larger than your out going air.
We measure duct pressure with a manometer in inches of water column.
We measure amount of air being moved with a tester that reads CFM per Min.
and also feet per Min. The feet per min. changes by using different size registers. later Paul

Jason96x

UPDATE

Upon further inspection of the return duct underneath the house, the entire return line is completely flex. There is a section around 8 feet long that is entirely collapsed. Im certain this is the cause of my problem. I re-installed the louver vent over the fresh air intake to keep the system functional. I know this is the worst way to try and heat a home, but until I get the money for the pipe to replace the return duct, this will have to do. Thanks for all your help guys!