I’ve been keeping my nose out of the new Public Works building that is going up to replace the barn that burned down last winter. Mostly, I’m just disgusted with the bunker mentality that the town has with regard to anyone questioning their building decisions.
But today, I was driving back from the dump and saw that they were pouring the slab floor of the building. I stopped and took a look. Here’s a picture of the prepared site:
You can see that it has some insulation and radiant heating tubes. Sounds great, but there are a few serious problems:
- The radiant tubes are at the bottom of the six inch slab. In other words, the tubes aren’t so much in the slab as under it. Any heat delivered through the tubes must pass through six inches of concrete to reach the interior of the building. I’ve read several accounts of radiant floor systems that have been abandoned (installed another kind of heat) because the tubes were installed this way. There is some suspicion that the radiant floor in the Pop-Whalen lobby was poured this way. That relatively small building burns more than 2,000 gallons of oil per year and barely maintains the desired temperature.
- The insulation under the floor is only 1″ thick. This is criminal, especially with the tubes right there against it. Guidelines for heated slabs in our climate zone call for at least three inches, typically four. There is a school of thought that “heat rises” so insulation is not necessary. That is wrong. Hot air rises, but heat conducts from hot to cold with no regard for direction. In this case, the ground is 50 degrees, the tubes will probably need to be 120 degrees or more. A large portion of the heat supplied to the tubes will simply go into the ground.
- There is no vapor barrier in the exposed spaces. The insulation board is taped and will provide some vapor resistance, though at only one inch thick not as much as a real membrane. But look at the huge spaces that are not insulated and have no vapor barrier. That’s just slipshod work.
This system as installed, if it works at all, will cost a small fortune to operate. Even with wood pellets for a fuel. Adding more insulation would have paid for itself in the first one-two years. Raising the tubes to the standard two inches from the surface would have been a little more work, but would have resulted in a system that actually works well to heat the space.
Here’s an analogy: Say you wanted to heat a basement that has six inch concrete walls. So you dig around the house and put tubing against the outside wall below grade. Then you cover that tubing with an inch of foam board and back fill. You then you connect the tubes to your boiler and try to heat up your foundation walls to heat your basement. Can you think of a better way to do it? Do you think it might work better if the tubes were imbedded near the inside of the foundation? How about if there was more insulation outside?
The pitch was that we would save money by having our Public Works director be the general contractor for this job. Instead we will end up paying year after year with inflated fuel bills, and probably have a problem keeping the place warm enough.