Your Place: Professor weighs in on insulation and ventilation

McClatchy-Tribune Information Services

I answered an insulation question in this column not too long ago, and Joe Ponessa sent me an email in late November about it.

"I don’t think you gave enough attention to the issue of combustion (makeup) air," said Ponessa, professor emeritus of housing, indoor environment and health at Rutgers Cooperative Extension.

Ponessa agreed that the limited work I described did not sound as if it would cause a problem for "atmospheric" combustion appliances, which derive their air from the surrounding environment.

There is, however, "a tipping point where draft-stopping will prevent adequate combustion air when all combustion appliances are operating simultaneously," Ponessa said. For this reason, "my colleagues who specialize in energy state that all weatherization projects should include a backdraft test to assure that combustion gas spillage does not occur."

He noted that he didn’t know where the line might be drawn between modest draft-stopping and that serious enough to warrant back-draft testing.

An expert should be able to offer some insight into this, he said, and "I think it would be a beneficial follow-up for your readers.

"By the way, I think that in most homes, air-pressure irregularities in the basement — driven by heating, ventilation, and air- conditioning equipment — will communicate to the upper floors, and certainly if there are ductwork registers — or duct leakage — in the basement," Ponessa said.

For an idea of the dynamics involved in airflows and exchanges, he offered the following example:

An oil burner, at a firing rate of one gallon per hour, draws about 1,600 cubic feet of air per hour; typical range hoods, about 200 to 400 cubic feet per minute.

If a house is "too tight," those units will compete for replacement air.

The resulting negative pressure will cause combustion spillage in the weaker appliance, he said.

Speaking of heating, don’t forget to have your furnace checked out by a professional before winter gets any older.

At least change the filter, following manufacturer’s recommendations.