Lining HVAC Under Floor Ducting And Managing The Risks!

“I have a customer who wants me to line his buried in floor heating ducting. He has an 8” diameter duct that was installed with Sonotube that has gotten wet and partially collapsed. The tube is buried in concrete and the floor above is Italian marble that cost $1,000 per square foot. The room is 30′ x 30′ square and the ducting follows the outside perimeter of the space with 90 degree turns at each corner. I can pull the downdraft furnace and install the liner through the line from the plenum. The installation would have me shoot downward for 8″, 90 degree turn toward the outside wall 8′ away, then a 90 degree turn heading to the outside turn 30′ down. It would then make another 90, go 30′ then turn again and go another 30′ finally making the final turn toward the plenum opening for 20′ back to the opening I began the liner from. I know 8″ liner is easier to install than 4″ so will this be a pretty easy risk free job?”


Typical HVAC 90

A couple of things you didn’t tell me. I assume the 90 degree turns are HVAC sharp 90’s at each corner? If so, the liner is going to want to stop at each sharp turn. You also didn’t tell me how you plan to remove the collapsed Sonotube and if using mechanical devices, will you disturb the bedding of the original installation that may impede this installation. Finally, if the marble floor is damaged, are replacement tiles matching this tile available if it is damaged?

So our challenge is to manage those risks and overcome the challenges as well as providing the cost adds for those risk factors to your pricing levels. In other words, would I charge the same money to do this 8″ job as I would if I lined 120′ of 8″ drain pipe that was in a straight line buried 2′ under grass? No. If I burn the grass, trample it, or spill something on it, a little grass seed or a few feet of sod will fix my problem and the last time I priced sod, it was no where near $1,000 per square foot.

My next challenge is to make sure I can get my liner to follow the Sonotube. I may shoot a pre-liner down the line to see if it negotiates the path I’m expecting it to take. If the pre-liner makes it, I’d leave it there and feel pretty confident that my liner will also make it. If it doesn’t make it, I’d try the same pre-liner with a pull strap attached that I could use to assist in helping the liner negotiate the path. If that worked, then I’d use the same approach to install the liner.

Pea Rock Bedding Around Pipe

And while we’ve put it at the tail of our scenario, getting the Solotube ready to line may be my biggest challenge. If pea rock were used as bedding, getting that back to round tube shape can be assisted with the pre-liner, but getting chunks of Sonotube out of the pipe may disturb other pea rock and cause it to fill your tube. Scrapers in the shape of the tube, only slightly smaller, may help move the original bedding material that is in the way back in place for lining.

My example above applies to this one job, but you should look at each job with the same critical eye. What are my risks? What will I do to manage those risks and what will it cost me to provide for those risks. What would the costs be if the work were performed some other way and what would those folks look at as risk? Once you consider your risks, profitability will follow, but if you don’t consider and manage risk, profitability will be pretty illusive. If you lose a job because your competitor didn’t consider risk, not to worry, they won’t be around for the long pull. And if you are open with your customer, you can go through the risks, tell them what you’ve included to provide for those risks and look to them to shoulder some of the risk if they are looking at cutting your cost by cutting your risks. If it’s a job that you don’t know whether or not you could do it and your customer is willing to pay you for the attempt and willing to cover any losses that occur because of your attempt, you can quote the work accordingly. If your customer isn’t of that frame of mind and wants you to carry all the risk, then you would price the job differently.

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