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Do homework before considering eliminating the chimney

QuestionHi! We've just renovated a '50s bungalow and have two 10-year-old gas furnaces venting through a chimney, even though there is no steel ductwork. I would like to replace the chimney with something less intrusive. Can we vent the furnaces directly outside through the side of our home or do we have to run new venting up through the roof? Also, what are the regulations for the type of venting required to replace this chimney?

AnswerYour questions give me the impression that you are looking for a way to eliminate the chimney. If there's a solution that will allow your heating appliances to be vented to a new location, what are your plans for the chimney?

Depending on where the chimney is located, you may gain extra space if you remove it. However, removing the chimney is a tremendous project and requires roof, ceiling, floor, and wall repairs as well as disposal of masonry products.

My other concern is the type of water heater you have. Since most homes with a gas furnace also have a gas water heater, I assume that you have a gas water heater. In most cases it vents into the same system as the furnace. If your water heater now vents into the chimney, it's another appliance to consider as you plan your project.

The simple answer to your question about venting through the sidewall is that it depends on your appliances. It appears from the way they are currently vented that you have 80-percent efficient furnaces, so check the installation manuals for sidewall venting options. If you don't have the owner's manuals, bring in a licensed serviceperson to assess the situation.

An option to consider is a sidewall power vent (induced draft fan). Basically, it's a fan located at the end of the exhaust pipe that mounts to the sidewall to improve draft and pull the exhaust combustion products to the outside. On the outside of the home, the vent hood is similar in design to that of a clothes dryer vent hood.

I think this is more attractive than a 90-plus efficient furnace venting through the sidewall with two PVC pipes, especially if you want to maintain the integrity of the home's appearance. An induced draft fan interlocks with the furnace system so it turns on before the furnace fires. To learn more about this system and see a diagram of an installed unit, go to www.tjernlund.com/gassidewall.htm.

Regarding the type of exhaust pipe to use, I believe an explanation of the difference between 80 percent and 90-percent-plus efficient furnaces will answer your question.

If the furnaces have draft hoods, they are about 67% efficient and can be vented with Type "B"-vent or into a masonry chimney. If the furnaces do not have draft hoods, but are fan-assist draft furnaces, they are from mid 1980s or later and are 78 to 83% efficient and need to be vented with Type "B"-vent or into a metal lined masonry chimney. If the furnaces have two plastic pipes coming out of the top of the furnace, they are 90% + efficient condensing furnaces and the plastic pipes bring in outside combustion air and vent the products of combustion to the outside.

Normally the 90% + efficient furnaces can be vented out the sidewall or through the roof; the other furnaces vent through the roof unless there is an induced draft fan installed on the sidewall. In any case the venting needs to be installed according to the furnace manufacturer's installation instructions, or with an induced draft fan, the venting will follow the induced draft fan manufacturer's installation instructions to allow sidewall venting.

If you decide to remove the chimney completely and vent in the same location using B-Vent, you can leave it as is or build a chimney chase around it, which will allow you to finish the exterior of the chase any way you want.

If you vent through the sidewall and carry the B-Vent up along the side of the home, you'll need to frame a chase around it and insulate it to limit the possibility of condensation within the pipe. Again, the exterior of the chase can be finished to complement the home's exterior.

In your case, you can handle the demolition portion of the project such as removing the chimney and repairing the roof, interior walls, etc. However, in Calgary homeowners are not allowed to work with appliances that involve natural gas. Permits for gas work are required and the work must be done by a certified mechanical contractor.

Also, the building and mechanical codes need to be followed.

There's no simple answer. You'll have to do some homework and work through a decision-making process to determine what's important to you. Good luck with your project!

Copyright © 2005, 2006, & 2007 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.


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