On Oct. 13, 2007, I made mention in this space of a pending class-action lawsuit against Carrier Corp., the manufacturer of Carrier, Bryant...

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On Oct. 13, 2007, I made mention in this space of a pending class-action lawsuit against Carrier Corp., the manufacturer of Carrier, Bryant, Payne and Day & Night brand 90 percent efficient furnaces. A settlement has been reached, subject only to a fairness hearing scheduled for next month.

As a result of that quick blurb, I received many reader questions about those furnaces. So let’s dive into the issue a bit deeper.

Your everyday gas furnace is 80 percent efficient. It loses 20 percent of the energy you pay for right up the chimney. Bye-bye heat, bye-bye dollars.

Superefficient furnaces, also referred to as 90 percent furnaces or condensing furnaces, eliminate half of that heat loss. This is one reason they have become so popular.

The addition of a secondary heat exchanger to extract heat from exhaust is what makes that efficiency difference. Much colder than conventional furnace exhaust, condensation occurs quickly within the pipe. All that water requires the exhaust system be fabricated out of plastic plumbing drainpipe.

Depending on configuration of the exhaust, some of the condensed moisture may be drained to the exterior of the building, with the remainder draining back toward the furnace.

It is that water running back toward the furnace that causes all the problems.

Carrier Corp. gets the blame, negative publicity and liability for faulty secondary heat exchangers made of polypropylene-laminated steel, but they are definitely not alone. I cannot think of a single manufacturer’s condensing furnace without a series of problems due to water. It is a design, installation and maintenance issue, not solely the fault of any particular manufacturer.

Once it drains down the exhaust pipe, that condensed water runs into the exhaust motor housing, where weepholes allow it to seep through a series of plastic tubes, collection buckets and finally into a pump — or to drain out of the house via gravity, if so configured. Problem is, those weepholes become clogged with ash after a few months of operation, and those tiny drain pipes become loose at their fittings or get brittle due to heat exposure and then leak.

The service person cleans all the drains, checks all the fittings and replaces the worn pipes. Without that regular maintenance, water backs up into the guts of the furnace and rusts it from the inside out. And the homeowner hasn’t a clue.

Without regular professional servicing, oil furnaces just up and quit. Some cold person in the house gets a clue and calls the heat guy.

Without regular professional servicing, 80 percent gas furnaces just run poorly and produce carbon monoxide. No one is the wiser. Without regular professional servicing, that 90 percent furnace just rusts itself into the scrap heap. No saving it. Either of the first two furnaces can be salvaged to run another day.

Without complications, and without expensive add-ons, it should cost roughly $2,500 to install an 80 percent furnace. Expect it to last 20 years. It will require professional servicing every two years for best efficiency and safety.

A 90 percent furnace in a similar situation will cost closer to $4,000, will require professional servicing every year and is more prone to breakdown — and you are lucky if it is still running in 15 years.

While I am all for saving energy, the math is pretty simple. These furnaces have been pushed hard by utility companies and heating contractors because of the need for energy efficiency and profit margins, respectively. Only a 90 percent furnace will work in some retrofit situations because the exhaust can be vented laterally and the combustion is typically sealed. And they work great when regularly serviced. Problem is, furnaces are the most neglected appliance in the house. And that should change.

To learn more about the claim and settlement, go to www.furnaceclaims.com. Settlement claim forms must be submitted by Aug. 1, 2008. All class members receive a secondary heat-exchanger warranty extension, and up to $270. Applicable furnace model numbers are on the Web site.

Darrell Hay is a local home inspector and manages several rental properties. Send e-mail to dhay@seattletimes.com. Sorry, no personal replies.