In-slab ducts

I never endorse in-slab ducts, tacitly or otherwise. Most of the in-slab ducts that I’ve seen have been deteriorated in one way or another. Naturally, any adverse conditions/components that affect air quality could result in a lawsuit. The most recent system with in-slab ducts that I inspected had new components that some misguided inspection company had approved. This happened to be in a multi-million dollar house with a combination of flat roofed sections and cathedral ceilings. The ducts were moisture contaminated and, after review by specialists, my client was compensated $50.000.00 before the close of escrow. That’s right, $50,000.00, which certainly made me seem like some sort of a hero. Why? Because I elected to remove several floor registers and peer inside, rather than rely on my standards that say I do not dismantle things, etc. The moral? Never, under any circumstances, endorse in-slab ducts.Back to top](**


NACHI Standards of practice

4. Glossary of Terms

4.1. Accessible: Can be approached or entered by the inspector safely, without difficulty, fear or danger.
(A floor register is easily accessible without difficulty, fear, or danger)
4.13. Dismantle: To open, take apart or remove any component, device or piece that would not typically be opened, taken apart or removed by an ordinary occupant.
(My wife removes floor regesters in our house to vacuum)

Be careful what you decide is not accessible or you dont dismantle. With that kind of money involved, you could easily be accused of negligence if you missed it.

Good info but I would not consider simply removing a floor register dimantling anything, no different than removing an access panel.

They were scewed in-place, but agreed. I removed a total of eight.

80% of the homes that I inspect are slab with down flow furnaces. I make it a standard procedure on all homes with ducts in the slab to remove all registers and observe down the duct with a mirror and flashlight to the first turn and if there is any visible evidence of past or present free standing water I recommend a full camera scan be performed. High water tables in my area is a common issue and as a home inspector you better be aware of which areas are subject to high levels or you will end up where you don’t want to be. In court???

Also as a incentive to check these ducts within this past year I found a pop-corn jar with $1101.00 stashed from some previous owner. Probally a little old lady.


I agree with you, not to endorse in slab ducts*.I think it’s important to inspect properly and report.

In your case, did you not have an duct cleanout access?

Just a few pointers for fellow HI.

Concrete min. 3" poured onto top of ducts.
Should be rigid spiral round duct not rectangular.
Check for cracking of concrete floor above ducts.[if possiable]
Internal signs of duct collapsing.
Duct cleanout access has to be provided.
Examine for rust and water.
Standing water should be pumped out.



It’s called “DUE DILIGENCE” sometimes you do what you have to do.And with this system you really should be checking.

Water should be pumped out.


There should be no free standing water in the ducts to be pumped out.


However if standing water is found it should be pumped out.


However if standing water is found it should be pumped out.

More important to determine the source of water in the ducts internal or external to the foundation. If you just pump the water out it is going to return and you have accomplished nothing.

Water in the ducts is a very common occurrence in this neck of the woods. The standard practice is to seal the ducts with concrete and install a up-flow furnace with the ducts in the attic. A real Realtors nightmare they do not like to hear water in the ducts as this can also be created by a drainage problem external to the foundation that also should be corrected.