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Duct Sealing
Why Central Texas Ducts Leak
Most ductwork here is flex duct strung through the attic and connected to sheet-metal boots and plenums. Every one of those connections was made with tape, a strap and maybe some mastic, and then it spent twenty summers at 130-plus degrees. Tape adhesive bakes off. Plastic straps get brittle. The duct sags, the joint opens a quarter inch, and the system starts pushing a share of its cooled air into the attic while the return sucks hot, dusty attic air back in.
You feel that as a bedroom that never cools, a filter that looks gray in two weeks, and a bill that grows every summer. Duct sealing closes those openings. We do it the old-fashioned way where we can reach the joints, with mastic and proper fasteners, and with Aeroseal when leaks are behind walls or inside chases where hands cannot go. We start with an inspection, because sealing a system that has a crushed run or an undersized return only fixes part of it.
You get a written price first, honored for 72 hours under the Home Comfort Guarantee, and Care Club members take 5% off with no dispatch fee.
- Mastic, not tape Tape is what failed in the first place. We seal reachable joints with mastic and mechanical fasteners that survive the attic.
- Aeroseal for the unreachable Leaks inside walls and ceilings get sealed from the inside, so the whole system is covered, not just the attic.
- Measured before and after We check airflow and pressure on both ends of the job, so you know the sealing did what we said it would.
What Leaky Ducts Look Like
Signs Your Ductwork Is Leaking
Leaks are invisible from the living room. These are the clues they leave behind.
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Rooms at the end of the run stay warm
By the time the air reaches the last register, a good share of it has already escaped into the attic.
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Summer bills keep rising
The system runs longer to hit the setpoint because part of what it produces never enters the house.
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Filters load up fast
A return leak draws attic dust and insulation fibers into the system. If the filter is dark in two weeks, suspect the return side.
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Sticky, humid rooms
In San Antonio especially, return leaks pull moist attic air in faster than the coil can dry it.
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A cool attic in July
If the attic near the air handler feels noticeably cooler than the rest, you are air conditioning it.
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Air movement you can feel in the attic
A breeze at a duct joint with the system running is a leak you can put your hand on.
What We Seal
Every Place a Duct System Lets Go
The leaks are rarely in the middle of a run. They are at the connections.
- Flex-to-metal connections Takeoffs at the plenum and collars at the boots, resealed with mastic and secured with proper straps.
- Boots and register openings The gap between the boot and the drywall is a leak into the ceiling cavity. We seal it.
- Plenums and air handler cabinet Seams, panel gaps and the filter slot. Leaks here are the biggest single source in many systems.
- Return chases and platforms Framed returns built into closets and platforms leak through every stud and joist gap. These matter as much as the supply side.
- Aeroseal for concealed ducts Runs inside walls, between floors or under a slab get sealed from within. See Aeroseal.
- Repair and replacement A run that is crushed, torn or chewed gets replaced, not sealed. We tell you which is which.
How It Works
How We Seal a Duct System
Most homes are done in a day. You will not need to leave.
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Inspect and measure
We trace the ducts, find the leaks, take airflow and pressure readings, and price the work in writing.
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Seal what we can reach
Joints, boots, plenum seams and the cabinet get mastic and fasteners. Damaged runs get replaced.
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Seal what we cannot
Where ducts are concealed, Aeroseal closes the remaining leaks from inside the system.
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Measure again
Airflow at the registers and pressure at the equipment, compared to the starting numbers, so you see the difference.
Current Specials
Save on the work your home needs most.
Paying to Cool an Attic You Never Use?
Get a written price for duct sealing in Austin or San Antonio, with no surprise fees.
What Our Customers Say
Don't just take our word for it — hear from our satisfied customers
★★★★★
Our 18 year old HVAC system finally gave out this past week, so we reached out to Radiant to see what could be done. They sent a tech out named Bryan the same day, and he did a great job looking over the entire HVAC system. He was friendly and helpful in explaining everything that he saw, and our options moving forward. We decided to replace the entire system, so we met with Jacob (same day thankfully) to find the best HVAC system for our needs. Jacob was friendly, professional, and did a great job explaining the different options on offer. Radiant was able to set-up next day install, which was much appreciated, because the temps were still going to be cold in the coming days.
The install team consisted of Carlos and Pablo, who were very courteous and professional, and were kind enough to answer any questions I had regarding the install. They did a great job installing our new HVAC system, and were tidy which is always appreciated! Before they left, they explained everything that had been done, and showed me photos of the work.
Our entire experience from start to finish was great. I appreciate that they send photos of who is coming to your home too. Friendly, kind, professional team members, and good work all the way around. Thanks Radiant!
The install team consisted of Carlos and Pablo, who were very courteous and professional, and were kind enough to answer any questions I had regarding the install. They did a great job installing our new HVAC system, and were tidy which is always appreciated! Before they left, they explained everything that had been done, and showed me photos of the work.
Our entire experience from start to finish was great. I appreciate that they send photos of who is coming to your home too. Friendly, kind, professional team members, and good work all the way around. Thanks Radiant!
★★★★★
This is the first time I’ve used radiant my neighbor recommended them…. I called them today and they set me up an appointment on the same day. I was totally shocked at that and the service call was only $39!!…. Highly recommend them Danielle showed up and he was a great guy and he put up with all my wishy-washiness and I had to hurry him because I was heading to church and he got caught in a lot of traffic getting here he even would’ve installed the part that broke but I Didn’t have the time tonight….. He was patient with me and just told me to call the office first thing in the morning and get a service call set up…. Thank you so much Radiant!!….
With another cold front coming in tomorrow now I just hope they can get me scheduled for a separate call tomorrow but I have a feeling they will. They are such a great company!!😊😊
With another cold front coming in tomorrow now I just hope they can get me scheduled for a separate call tomorrow but I have a feeling they will. They are such a great company!!😊😊
★★★★★
Alex performed the winter service on my unit. This business along with Alex, are very professional and upfront about everything. To be transparent, this is the maintenance included with the purchase of a unit from them. I was informed about everything to include pictures as proof. I was told that my unit is 100% and very clean and again pictures to prove it. I was reccomended this business by a friend and glad he did. The initial purchase experience was also amazing. I had contacted 5 other businesses to get quotes about a new unit as my upstairs unit failed. 2 were outrageous quotes and I am technically still waiting on the other 3. On every instance of getting a quote, I waited about 1 week. Luckily my house has two units but still, un acceptable especially during the summer. I guess they all had so much business they did not care for mine. When I called this business not only did they come out the same day, I had the new unit installed with in 48 hrs. Oh and let's not forget the quote they gave me was the lowest of all. I can say enough good things about this business. Keep up the great work.
Maintenance Membership
Join the Care Club
Home maintenance for $9.99 a month.
Care Club members get two HVAC tune-ups and a plumbing safety inspection every year, priority scheduling, no dispatch fees — ever — and 5% off every repair.
- Priority scheduling
- Seasonal HVAC tune-ups
- Annual safety inspection
- Exclusive member discounts
- Free dispatch on repairs
- No long-term contracts
Duct Sealing Questions
How can I tell if my ducts are leaking without going into the attic?
Two quick checks. First, with the system running, hold a hand at each register and compare. If one or two are weak while the rest are strong, the run feeding them is probably leaking or kinked. Second, look at your filter after two weeks. If it is loaded with gray dust and fibers that look like attic insulation, the return side is pulling unfiltered air from the attic. Rooms that feel sticky in summer point the same way. None of these prove it, which is why we measure airflow and static pressure during an inspection before recommending sealing.
Why not just use duct tape?
Because that is usually what failed. Cloth duct tape was never meant for ductwork, and even the foil tapes rated for it dry out and let go after enough summers at attic temperatures. Mastic is a thick paste that cures into a flexible, permanent seal over the joint, and it does not depend on adhesive holding onto a dusty surface. Combined with proper mechanical straps on flex connections, it holds up through the heat. For leaks we cannot reach, Aeroseal seals from inside the duct. Either way, the goal is a repair you do not redo in five years.
Will sealing the ducts change how the system feels?
Usually the first thing homeowners notice is the far rooms finally matching the thermostat, because air that used to leak into the attic now arrives where it should. The system also tends to run shorter cycles to reach the setpoint. One thing to know: sealing raises the pressure inside the ducts slightly, since air has fewer places to escape. On a system with an undersized return or a restrictive filter, that can show up as more noise at the return grille. Our before-and-after measurements catch that, and if the return needs attention we will tell you rather than leave you with a new problem.
Should I add attic insulation at the same time?
They solve different problems and work well together. Duct sealing stops conditioned air from escaping and attic air from entering the system. Insulation slows the heat that soaks through the ceiling into the house and through the duct jacket into the air. If the ducts are leaking badly, sealing comes first; there is little point insulating around a duct that is blowing cold air into the attic. If the ducts test tight and the attic is thin on insulation, that is the better next spend. We can look at both during the same visit and give you a written price for each so you can decide what to do and when.
*Offers cannot be combined with other promotions or applied to dispatch fees. No cash value. Must present offer at time of service. Call for details.
