Eliminating Return Duct Runs

michigan roman

1950's 1200 sq' block ranch home on a crawl with a down flow furnace ,
the oval pipe type return ducts in attic are pretty beat up and have alot of kinked in / loose joints between the oval sections of duct . and into these openings the blown in paper insulation has been getting into for years . and i guess it makes the home very dusty , the entire inner return duct system is dusted with the insulation dust . and in the utility room with furnace the return boot / plenum goes up into attic and also has a 6" round run running 6' away from furnace and thru wall on dining room on other side , and directly off the boot / plenum theres another vent thru wall into the kitchen right next to dining room . and im wondering if i were to go in attic and disconnect all the return runs in the attic and seal off the boot / plenum rising into the attic and just keep the two utility room return air feeds to the furnace would this cause a problem ? i want to do this to stop the big dust problem . and fyi the furnace is at one end of house , and all the return runs i want to eliminate run all the way down to bedrooms etc at other end of house .

hvaclover

No you may not do this.

You are saying these are rigid pipe and not flex? Rigid pipe that has spaces in it that is sucking attic insulation.

Is there a cold air trunk in the attic that has branch pipes going to your individual rooms?

Very unusual to have a cold air in the kitchen No knowledgeable Pro would do that.

The small area you propose to use as R/A is not large enough to run the furnace safely.

michigan roman

thanx for reply . yes these are rigid old oval / flatish type say 12 " in diameter pipes running as the main return trunk in attic , it runs back to the main return boot sticking through the ceiling from the furnace . i was hoping for an easy fix because the pipe lengths are all say 6' , the main line and each run from that line to individual rooms , and many of the unions between lengths have been sat on or kneeled on by people working in / using attic so ide have to dig out around each joint in all the dusty paper insulation and reshape the pipe then i guess tape it secure . then i guess have the return run vacumed out by one of those big trucks . alot of dusty work plus some cost as opposed to sealing off the runs .

though im wondering in this say 30 x 50 home would i have to keep all the runs intact or could i just seal up / fix a few of the ones nearest the trunk and eliminate the rest ? can you tell i dont want the job in that dusty old insulation

neolitic

You may want to cut down the
return air, but the furnace doesn't
want you to.
The supply and the return need
to be balanced to work.
Why not run new return ducts?

hvaclover

Well since I live in Mi too I have a "feel" for the types of construction in our state.

I would just replace the bad pieces. It's not that hard and oval pipe is still common these days. Easy DIY project.

Just stay away from Lowes and HD for duct fittings. They charge so much the cashiers should be wearing masks and holding a gun on you when you pay for it.

Decide to do it yourself PM me ....assuming i have PM ...I'm new here to, if not post back here an i can put you in touch with somebody who will sell fittings to you at reasonable price.

spheatandair

You can download a heat loss calculator to help you size the ducting. allowing you to see how much return and supply ducting you need to allow proper air flow at http://www.hvaccomputer.com/