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Duct sealing


lmacmil's Avatar
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11-20-09, 09:46 AM   #1  
Duct sealing

I have a gas forced air system in a house built in 1970 (replaced the furnace in 1997). I'm wondering if there is any payback to sealing the ducts I can get at (essentially just the basement). I read somewhere that leaky ducts account for 10-30% of heating cost (the 10% figure seems believable but not 30%).

Ductwork is the standard galvanized sheet metal. My plan would be to use aluminum foil tape (not duct tape!) and seal every seam I can access. The only cost will be the tape. My time is worthless!

Opinions?

 
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11-20-09, 10:17 AM   #2  
Excellent idea. Sealing ducts can save a lot and even the 30% when they are located outside the conditioned spaces, sttic or crawl space. Inside your home, the alr that leaks out is still inside the home, but maybe not where you want it. Where leaky ducts inside a home create a problem is by pressurizing some areas and depressurizing others. Example: if warm air is leaking into the basement, then the return side must draw replacement air from somewhere, often outside. By sealing everything you can reach, you will be sending the majority of the heat to where it was intended and returning same. Even 5% would be worth while.

But, while you are at it, air sealing the house is perhaps the number one for easy projects and rate of return. I can provide more details if you want more work .

Bud

 
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11-20-09, 12:40 PM   #3  
Posted By: Bud9051 But, while you are at it, air sealing the house is perhaps the number one for easy projects and rate of return. I can provide more details if you want more work .

Bud
I assume you are talking about caulking around ceiling fixtures? I thought about that but decided it was too big a pain. I think I have 7 or 8 that are accessible (and I use the term loosely) in my attic. Locating them under 6" of blown insulation topped with 12" batts would be a real challenge. Should have done it before I put the batts down several years ago. I've got those foam thingies under every switchplate that's on an outside wall.

What else else I should look at?

 
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11-20-09, 02:47 PM   #4  
The list for air sealing is rather long and as you mentioned, not always easy to get to. If the basement is open, that is a good place to start. All electrical wires, and plumbing holes can be foamed or caulked. Always use a fire rated product. Bath tubs and shower drains can often have larger gaps, so some sheet metal or sheet rock with the foam is best.

The foam inserts for electrical boxes help, but do not seal around the edges of the box, the box to sheetrock gap. I like to cover the entire switch or outlet with contact paper, cut out for the particular device. Then reinstall the cover and trim as desired. Some cases flush looks best and others when the colors match allow a border as wide as you like. Helps with finger prints. Shelf paper is a low tack contact paper and comes in many colors. The objective is to block air flow in or out of all boxes, not just exterior walls. Since the sheetrock is not glued/sealed to the studs, any air that enters a wlaa cavity has full access to the attic. Unlike the floors where walls were set on top of plywood, the top of your walls is just under all of that insulation, which means the sheetrock to wood interface is open to the attic. Cellulose can slow air leakage, but fiberglass does little.

Around the chimney and any other vents. Above drop ceilings over cabinets and plumbing under sinks. Recessed lights as mentioned, at all levels. Forced air heating systems have their own list of issues.

Because there are many ways to construct a home, some areas in your home are a problem and others are not. A porch roof on a two story may have large air bypasses if it was installed before the sheathing went on. Dormers, kneewalls, garage attics and many other spaces all need to be checked. Also hatches or pull down stairs need to be insulated and air sealed.

Long enough, the rest we can catch next year.
Bud

 
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11-21-09, 08:12 AM   #5  
Posted By: Bud9051 Excellent idea. Sealing ducts can save a lot and even the 30% when they are located outside the conditioned spaces, attic or crawl space.
One more duct sealing question. I have two types of seams. One is a simple "one tube inside another" with rivets holding them together. Those are clearly not air tight.

What about the "wrap-around" seams used in the rectangular ducts or the swivel-type seams that let round ducts change direction? Those look like they seal pretty well though probably not airtight.

 
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11-21-09, 08:25 AM   #6  
Air tight is what you want. Where they are easy to get to, I would do all.

Bud

 
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