HVAC companies replace the unit and leave the return plenum. Twenty years of damp insulation then feeds the brand-new system. What a plenum is, how to check yours, and what replacement involves.
When you get a new air conditioner, the outdoor unit and the air handler are replaced. The return plenum, the sheet-metal or ductboard box that collects air from the house and feeds it to the air handler, almost never is. It is the oldest part of the system and the one nobody looks at.
Take the return grille off the wall or ceiling and you are looking into the plenum. It is usually lined with fiberglass insulation to quiet the airflow. That lining is porous, it sits in the damp air stream all summer, and it catches everything the filter misses. After 15 or 20 years it is black.
Everything the system delivers passes through this box first. A plenum with microbial growth means a coil with microbial growth in a year no matter how new the unit is, and a musty smell in every room. In a Georgetown-area home we inspected for a buyer, the unit was three years old and the plenum was the original twenty-year-old one, black inside. The fix was the plenum, not the unit.
The old box comes out, a new sealed plenum goes in with a cleanable liner or none, the filter rack is fitted properly, and the seams are sealed. Half a day on most homes. We photograph the old box on the way out, and customers usually keep the photo to show the neighbors.
See what Air Duct Busters customers have shared about the work completed, their experience with our team, and the service they received.
They came to do the full inspection of our HVAC system and performed a thorough inspection with photos and a very detailed list of quoted recommendations. Gary and team were punctual the 3 times they came to our home and their price was very reasonable.
Read on GoogleNoah took the time to show us photos from inside the vents and ductwork and clearly explained the level of cleaning needed and why. We really appreciated the transparency and education instead of feeling pressured.
Read on GoogleGary inspected the plenum, there was microbial growth in the insulation. The system was replaced 3 years ago but had the original 20 year old plenum. Gary replaced the plenum and installed a scrubber. We haven't had any allergy problems in our new home so far.
Read on GoogleNoah was professional, knowledgeable, and extremely thorough while working on both my air ducts and chimney. He took the time to explain everything and made sure the work was done properly from start to finish.
Read on GoogleShort reads from the crew: what we find in Hill Country homes, what it costs, and what to do about it.
From our job log in Lampasas: 6 recent visits for chimney and fireplace, dryer vent, ductwork. Photos from the crew, work as written on the invoice.
September 7, 2026 · 3 min read
From our job log in Burnet: 8 recent visits for chimney and fireplace, dryer vent, ductwork. Photos from the crew, work as written on the invoice.
September 7, 2026 · 4 min read
From our job log in Horseshoe Bay: 8 recent visits for ductwork, dryer vent, microbial growth and air quality. Photos from the crew, work as written on the invoice.
September 7, 2026 · 4 min read
Leave a number and we call you back within the hour to set a window. The inspection costs nothing and you decide afterwards.