What are the problems with underground return air ducts?

Wednesday, October 9, 2019

Under-floor-slab return air ducts were briefly popular in our North Florida area during the late 1950s and early 1960s. They were usually in upscale, midcentury modern homes. We guess it was considered cutting edge technology at the time, but now these old underground ducts are a liability for two reasons: 

  1. Corrosion and settlement have created openings in the ducts over the years. Because the return air is a suction, it pulls any gases and moisture out of the soil. Several areas around Gainesville and Ocala have elevated radon in the ground, and the ducts essentially suck the radon into the air flow, elevating interior radon levels.


  2. During the wet season, when the water table rises, we have inspected houses with standing in these ducts.


    The ducts terminate directly under the furnace/air handler in most homes. So they can be abandoned and sealed at the floor level, and the return air rerouted to the attic—except that many midcentury modern homes are flat roofed and have no attic. The solution then is typically adding a soffit along the ceiling to enclose the new duct. 

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 

  To learn more about heating and air conditioning systems, see these other blog posts:

How can I find out the SEER of my air conditioner? 

My air conditioner won't turn on. What's wrong? 

How can I find out the size of my air conditioner? 

How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

Where is the air filter for my central air conditioner and furnace? I can’t find it? 

Does an old air conditioner use more electricity as it ages? 

How did homes stay cool in Florida before air conditioning? 

What is wrong with an air conditioner when the air flow out of the vents is low?

Why has the thermostat screen gone blank? 

Why does it take so long to cool a house when an air conditioner has been off for a while? 

Why is my air conditioner not cooling enough? 

What are the most common problems with wall/window air conditioners?  

Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING and RADON pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles. 

How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactued and modular homes

(placeholder)

Search

This

Site

Search

This

Site

Attics

Air Conditioner & Furnace Age

AFCI, CAFCI, DFCI, & GFCI

Bathrooms

Aging in Place

Appliances

Click Below  

for Links to Collections

of Blog Posts

by Subject

Cracks

Doors and Windows

Electrical

Energy Efficiency

Fireplaces and Chimneys

Heating and Air Conditioning

Home Inspection

Hurricane Resistance

Electric Receptacle Outlets

Electric Panels

Garages and Carports

Common Problems

Exterior Walls & Structures

Insulation

Insurance

Life Expectancy

Mobile/Manufactured Homes

Older and Historic Houses

Mold, Lead & Other Contaminants

Modular Homes

Metal Roofs

Plumbing

Radon

Pool and Spa

Roof and Attic

Remodeling

Safety

Site

"Should I Buy A..."

Stairs

Termites, Wood Rot & Pests

Structure and Rooms

Wells

Water Heaters

Water Heater Age

Septic Tank Systems

Plumbing Pipes

Sinkholes

When It First Became Code

Park Model Homes

Shingle Roofs

Stucco

Wind Mitigation Form

"Does A Home

Inspector...?"

"What Is The Difference Between..."

Brick

Concrete and Concrete Block

Foundations

4-Point Inspections

Rain Gutters

Condominiums

Crawl Spaces

Building Permits

Clay Soil

Floors

Toilets

Generators

HUD-Code for Mobile Homes

Flat Roofs

Sprinkler Systems