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posted: 8/12/2012 5:00 AM

Home repair: Ductwork insulation may help air conditioner's efficiency

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Q. I have a question regarding air conditioning. I live in a slab home in western Pennsylvania. The home is heated by a water system that is in the slab. Cooling is done with the heat exchanger in the attic, and the compressor in the standard exterior location. Our home only has flexible cooling ducts that go to vents in the ceiling, no duct work in the walls. I noted that off the heat exchanger in the attic is a standard metal duct which forms the main manifold, and off this manifold are flexible lines that appear to be made of an insulation material.

However, the main metal duct that comes from the heat exchanger has no insulation. Since the attic can reach temperatures well over 100 degrees during the air-conditioning season, the uninsulated manifold would allow for a lot of heat transfer. Would there be any downside to insulating the manifold exterior with, say, 3-inch-thick Styrofoam. If acceptable to insulate, any suggestion how to hold the Styrofoam onto the duct. Gravity will help hold the insulation onto the manifold. The horizontal heat exchanged has a pan under it for condensation that runs to a drain.

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A. The main trunk may be insulated inside, but it is quite inadequate in your hot attic installation.

Your plan is very sound. You may want to consider 2-inch-thick polyiso, which has a reflective aluminum foil, although 2-inch-thick XPS (Styrofoam or FoamulaR) is also fine. If you choose XPS, you can adhere the rigid insulation to the metal with either Styrobond or a polyurethane caulking compound; both compatible with XPS. If you choose polyiso, you can use the same sealant/adhesive, although other types are also OK. Be aware that the aluminum skin is very fragile and peels off easily.

If you use polyiso, try to cut the pieces lengthwise with a bevel to keep the reflective foil uninterrupted. Use strips of duct tape every foot or so to hold the pieces together, and secure the entire envelope with one-quarter inch nylon rope, which will not cut into the insulation.

Q. Several months ago we had chocolate cherry mulch put on our flower beds as we did last year. For some unknown reason, several weeks ago the robins started wreaking havoc with the mulch all along our curved sidewalk. This happens not once but generally 3 to 4 times a day and looks absolutely horrible.

We have tried several different applications that were supposed to keep the robins out. It doesn't work!

Hoping you can provide some known solutions to this problem. We don't mind the robins at all but we just want our mulch left intact.

A. Have you contacted the people who delivered the mulch to find out if they have heard of similar situations? I have contacted several sources of mulch, but no one has heard of such a problem. The only thing that comes to mind is that the cherry mulch, like any other organic mulch, is providing an environment that encourages earthworms and insects, which are relished by the robins. Or perhaps there is something about cherry mulch that makes good nesting material.

Interestingly enough, no one I contacted knows anything about cherry mulch; they all carry soft and hardwood mulches, but no cherry.

Q. I have been thinking pretty much forever about building my dream house. I live in the Northwest suburbs of Chicago and read your column in the Daily Herald as often as I can. I contracted my house 27 years ago and have had the urge to do it again at some point in the future.

While looking for your book, it occurred to me that you would do a wonderful job helping those of us considering a new house -- a book that inventories the latest tips on construction methods, materials and energy-efficient technology. My long-term plan is to construct a home with as many intelligent features as possible, including the latest material technology.

I would love to throw the kitchen sink at this new home, things like photovoltaic solar panels, hot air solar panels and water heat solar panels, geothermal heat, super insulation, solar orientation as well as many materials that could make the most sense for longevity, like a lifetime roof, cement siding and upgrades to the foundation and footings, etc.

A. Your humongous letter is so full of interesting questions that I will try to answer them over time. So look for further answers over the next few weeks.

Writing and having a book (such as the one you suggest) published takes a considerable amount of time, and by the time it becomes available, the material is already outdated -- so quickly things change in this field.

The best way to keep abreast of these technological advances is to keep following them as they develop and change. This is what I try to do in this column, one subject at a time. Thank you for your kind words and keep listening.

Q. I have checked to make sure that the baffles at the eaves provide enough opening for air movement from the soffit vents to the ridge vent, which runs just about the whole length of the roof, so my attic ventilation should be OK.

I'm probably over-thinking things, but I want to maximize ventilation. I've even considered strategic placement of fans on the attic floor to push air up toward the ridge vent.

A. The normal flow of air provided by full-length soffit and ridge vents is sufficient to ventilate an attic not contaminated by convective airflow from the conditioned living space. Adding more ventilation by means of fans can only mess up with the natural air movement provided by thermal energy. It has been proved to draw conditioned air summer and winter, adding to the cost of energy used.

Q. Would the XPS or polyiso insulation that you suggest installing under new vinyl siding help to keep the heat outside in the summer? I have a south facing rear wall on my house, 78-by-15 feet, and all five rear rooms are really warm in the summer. Any cost comparisons between the XPS, polyiso and regular Tyvek housewrap?

A. Any rigid insulation added to exterior walls will work in both directions, reducing the temperature fluctuation within the walls. In the winter, it will reduce the heat loss to the cold outside, and in the summer, it will keep the outside heat at bay, preventing the walls from heating up and radiating heat inside.

It will help reduce the cost of air conditioning and heating, while improving the comfort to the occupants by minimizing the heat transfer from their bodies toward the cold walls or the heat radiation from the hot walls.

But don't forget that unshaded windows, either by properly designed overhangs, awnings or shades, will admit a considerable amount of heat on west- and south-facing walls.

There is no longer a cost difference per square foot between XPS and polyiso rigid insulation. Tyvek is not needed if the joints between the sheets of rigid insulation are taped, saving a considerable expense. The rigid insulation will serve as an air barrier and protect the walls from any water intrusion getting behind the vinyl siding.

Q. My wife and I live in an old house that, in the summer, gets a somewhat musty smell. If we ventilate the house, it goes away. But, on hot days, we keep the windows and doors closed. Any tips for getting rid of the smell?

A. Please don't apologize. All pertinent questions are valid and welcomed. That is why I have been writing this column for more than 38 years.

The musty smell is likely to be ingrained in the house and may be difficult to pinpoint or eliminate.

If you have a lot of exposed wood, like wood beams and posts and old barn board paneling typically found in these old houses, try spraying them with Magic Zymes (www.magic-zymes.com). The manufacturer claims that it does not stain.

If you also have an old cellar with logs for the first-floor framing, perhaps even with bark on them, liberally spray Magic Zymes on them. If the floor is bare dirt, cover it with 6-mil plastic to contain the dampness to the soil.

I hope that it will work for you. Let me know; it's always helpful to know what works and what does not.

Q. What do you think about the Behr deck solid stains? There is a regular one and a premium one. Do you know if there are any differences? None of the places that you mentioned, except Glidden, carries the Wolman deck stains you mentioned.

A. Behr stains, available in Home Depot, have not performed well, in my experience. I have consulted with several condo associations that used them and were plagued with severe peeling problems. The manufacturer claimed that the peeling was due to improper preparation or application, which may be the case, since I was not privy to either in any of the cases I worked on. Several readers have also reported similar experiences.

Wolman stains are widely distributed in many markets. There is a very good substitute for decks, siding, wood roofs, fences, etc. It's Amteco's TWP, which I have used extensively and recommended over many years. Glidden stores may carry Amteco stains. Give it a try. You can check out Amteco's products at www.amteco.com.

Q. After purchasing our house, we noticed our concrete porch leaks water through a few hairline cracks and into the garage underneath the porch during heavy rain or snow melt. The cracks typically extend about halfway across the porch, but at least one is longer. The porch clearly hasn't been painted in several years as almost all of the previous finish is gone. We are planning to paint the porch to seal the concrete anyway but also would like to find a product that can seal the hairline cracks. Do you have any recommendations?

Also, what do you recommend for sealing between the house and the concrete slab at the joint? Would paint be sufficient for small gaps?

A. Hairline cracks are very hard to seal and waterproof. You need to saw-cut the cracks open first. This can be done by using a masonry blade on a circular saw, which is easier than it sounds. Wear safety glasses and a dust mask. Adjust the saw blade to the proper depth, retract the saw-guard back, and widen the cracks to approximately -inch wide by -inch deep. If you have someone else to help you, a Shopvac can be used to suck up the dust as you are cutting. Clean the cracks well, and mask either side for a cleaner job. Fill the cracks with Sikaflex-1a polyurethane caulking/sealant, using a putty knife to tool it and finish it flush with the surface. Pull the tape off and let the caulking air-cure for a few days. Clean the slab thoroughly with TSP-PF to remove any pollutants before painting it with a concrete paint.

You can buy Sikaflex polyurethane sealant in the Home Depot masonry aisle or order it from any A.H. Harris stores (www.ahharris.com).

Interesting new product: Smoke detectors are lifesaving devices that every home should have in all the recommended locations. However, if no one is home when a fire starts, it is of little help to save the structure.

Monitoring has been available through alarm companies, where the detectors ring a central station. But not everyone has an expensive alarm system.

Direct Connect 911 Smoke Detector works like a standard smoke detector that is installed on a wall or ceiling, and calls a central station when it is triggered by an incident.

It is an interesting product, and you can read more about it at www.directconnect911.com.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. Write to him in care of the Daily Herald, P.O. Box 280, Arlington Heights, IL 60006, or via email at henridemarne@gmavt.net. His book, "About the House," is available at www.upperaccess.com and in bookstores.

2012, United Feature Syndicate Inc.

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