Problem with furnace intake pipe

Q. My question concerns the exhaust/intake pipe for our forced air oil furnace. The exhaust pipe is inside the intake pipe. Both are mounted outside the house about 1 foot above ground level. We are told this is within town code and cannot be changed. The problem is drifting/blowing snow accumulates between the exhaust and the intake pipe. Since the exhaust is hot it melts the snow. When the heat is off the melted snow freezes into ice on the lip of the intake pipe. After several times of this happening the ice clogs the intake pipe and air cannot be brought into the furnace. Because the furnace cannot draw any air, it shuts down.

We must constantly check and clear the ice from the vent or we have this recurring problem. Is there anything we can do to prevent this from occurring? Is there some type of cover that we can attach that diverts the snow while at the same time allows enough air to enter the intake pipe?

A. The standard rule of thumb is that the exhaust/intake pipe should be 12 inches above the snow grade, not 12 inches above ground.

In the Northeast, the snow grade is considered to be 24 inches on average, although, with snow drifting, the snow cover may even be greater than 24 inches. The pipe should be a minimum of 3 feet off the ground and the pipe should slant slightly downward. This may be the cause of your problem.

You may want to have an experienced HVAC contractor look over the situation, see if the pipe could be changed to allow for more clearance from the ground. However, if not, the contractor may make some appropriate suggestions considering the actual layout of the area around the pipe.

Q. Ice was heard falling inside our natural gas furnace and hot water chimney when weather was ranging between about zero and 25 degrees for about 10 days recently. Our house is a raised ranch with the furnace and hot water heater on the lower level. The flue is 6 inches in diameter that discharges about 24 inches above the roof with a hood about 6 inches over the top of the 6-inch diameter opening. Is there a better design?

A. As I understand it, both the furnace and the water heater are vented into the same flue.

If both of your appliances are newer, efficient models, they should have been vented through a band joist and not through a vertical chimney through the roof. The gases of these efficient appliances are so much cooler than those of pre-efficient appliances that their water vapor content is prone to freezing on cold outside metal surfaces - in this case, the metal cap.

But if your appliances are older, the use of a vertical chimney through the roof is standard.

Is this a recent problem? If the cap is flat, condensation may turn into icicles and fall off for a variety of reasons - temperature changes, their weight overcoming their ability to remain attached to the metal cap, etc. A tunnellike cap may prevent this from happening.

The icicles drop down and will quickly become liquid again. It's important to check where they fall to make sure they will not interfere with the safety and operation of either of the appliances. An HVAC contractor can tell you if it is a problem and suggest a solution. But, if it is not a problem, is this so annoying that it is worth changing the cap without the certainty that it will be the solution? After all, this is only a seasonal annoyance of short duration.

Q. Do you know if the following problem is addressed by Englert's one-piece LeafGuard gutter system? My house is on a suburban lot with several oak trees. My gutters are capped with covers that are designed using the physics principle of "liquid adhesion." Every spring, the oak trees drop their catkins and when they are moistened by rain, the perforated openings in the gutter hood tracks get clogged. Instead of draining into the gutter, the rainwater runs over the gutter hood. I have had to get on a ladder to sweep the hood channel with a whisk broom to clear the clogged track. LeafGuard advertises a lifetime "clog-free guarantee." My gutter caps never get clogged with leaves; however, oak tree catkins are another story. I would appreciate any information you may have regarding this catkin-clogging issue before I get involved with a LeafGuard sales person.

A. The Englert LeafGuard gutter system uses an oversize gutter and 3-inch by 4-inch downspouts, the same dimensions of commercial gutters. They are simply commercial gutters and spouts with a cap added.

They work on the same principle: all roof debris will follow the cap and end up into the gutter from where they flow down into the commercial-type downspout.

So ask yourself if it is worth the very high extra cost of the LeafGuard gutters when you can get the same results by changing your residential gutters to the commercial types, which cost only about a dollar more per foot than residential ones.

Most gutter specialists offer both residential and commercial systems.

Q. Have you had any experience with the rapid mold killers that can be seen on YouTube and other such websites? I'm curious about their effectiveness and whether they truly kill mold or just cover it. I've read your columns concerning black mold, how it's caused and how to stop it. After a recent energy audit I'm planning to have a crew add more insulation in my attic, but before they start I need to kill the mold. With the work they and I are doing, I believe it won't be back but for them to work safely I want to kill it.

A. I assume you are speaking of mold on your attic's sheathing.

The mold has developed because warm, moist air has convected into the attic from the conditioned space below.

Adding insulation without first addressing the convection problem will make it worse because adding insulation will reduce the attic's temperature, leading to higher relative humidity (RH). I hope the energy audit pointed that out and is addressing it.

Once the convection issue is corrected, the mold will die of its own, but if you insist on dealing with it, try spraying it with a solution of one part fresh Clorox bleach to three-parts water or spray Wet & Forget on it (www.wetandforget.com.)

• Henri de Marne, a former remodeling contractor turned columnist and consultant, is the author of "About the House with Henri de Marne" (Upper Access Publishing). He continues to take questions from readers for this column and his website, www.henridemarne.com. Email questions to aboutthehouse@gmavt.net.