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Zoning a HVAC System - Ducts under slab

Trinkie's picture

We just moved into a new house and have a problem with the forced-air heating system for the bedrooms (separate from the rest of the house). The master gets most of the air flow and the other two bedrooms get very little, so they are cold most of the time.

The HVAC contractor says solve the problem by closing vents in the master. Even with all these vents closed, the other rooms still don't get very warm; besides, the whistling air from the closed vents is VERY noisy.

The ducts run under a slab on grade, and the contractor says he can't zone the system now, as I would like to do. He says the ducts don't separate until they are under the slab.

Does anyone know of a solution or products that address this problem?

Thanks, Trinkie

(post #114827, reply #1 of 3)

Find a contractor that cleans ducts and has a fiber optics cable camera. I sounds like you may have some blockage in the duct(s) leading to the two cold bedrooms.

I am not familiar with downflow forced air or under slab duct work so the above would be my "best money to spend" start. I have used a contractor with the TV and camera set up to find problems in drain lines and locate a tee in a 2" water service. a good operator can get you within a foot of the problem spot.

You said "new house", is that new construction or just new to your family?



(post #114827, reply #2 of 3)

Thanks, Dave. I was going to get the ductwork cleaned anyway, so this is a perfect solution.

The house is brand new but the floor register openings weren't always covered during construction, so there could indeed be large debris down there. There certainly is plenty of dust and small pebbles.


(post #114827, reply #3 of 3)

I believe that they are damping valves that can be installed under the resisters or in place of the registers.

But all that does is automate what has been done. And that does not work.

Either the under ducts are undersized or blocked.

A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
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