Leaky ducts in concrete foundation
The recent article in FH#202 on HVAC efficiency (Is your heating system an energy beast?) addressed air leaks as a major source of waste, but offered no insight into the particular problem I have: my ductwork is located in the concrete foundation of my mid-1970’s house, and over the years root penetration and water leaks have caused rot and leakage.
None of the HVAC companies in the area seem to have any ideas how to deal with solving this. They say replacing the ducting would be ‘impossible’, and don’t want to touch the job partly because there’s a reg in my county that when replacing a central HVAC unit, the duct leakage must be certified as less than 50% or they can’t install a new unit without repairing the leaks first.
I had considered trying one of these pressurized ‘airseal’-type solutions but most companies say that is effective only when there are tiny little pinhole-type leaks, and they don’t want to get involved either.
There must be some creative solutions out there – does anybody have any ideas?
Thanks.
Replies
There's probably essentially zero air leakage, at the low pressure that duct leakage would be measured, since soil seals where the ducts have rotted through. (Though gaps left from rotted roots might be a small problem.) This of course doesn't mean that there's no heat loss (by conduction), but that's not the issue you're facing. I'd look into getting someone to actually measure the air loss for you.
If you want the ducts fixed I think your only options are 1) to dig up the slab and replace them, or 2) abandon them and put ducts in the ceiling. There are companies (a division of Pentair comes to mind) that grout-seal drain pipes, but doing this for heating ducts would be impractical, I suspect. At the very least all the corners and junctions would have to be dug up.
bcaka,
Look into Spacepak or Unico miniduct systems.
KK
A couple of thoughts. 1) A hvac guy or an energy auditor can pressurize the ducts to see how much air you are actually loosing. If not much like less than 500 cfm don't worry about it. If lots call your local sanitation utility. 2) There are companies that line their pipes that could line your duct. Some do small jobs. Get some names and start calling.