Attic fans are seldom helpful

Q.  My wife and I are fans of your blog. And speaking of fans…

We have read several of your opinions recently about attic fans, and I understand your reluctance to install one that might pull heated or cooled air from the living spaces below when you didn’t want it to. But, on summer days when it has cooled down outside, and inside the house, it is still oppressively steamy, wouldn’t an attic fan (either fixed in the gable end, or in the attic floor), combined with an open attic door and open house windows, pull in the fresh, cool outside air to make it bearable inside?

This condition of cool evening air seems to be common in Vermont in summer, and it seems to me that an attic fan might be cheaper than installing air conditioners in key rooms. What do you think?

Whole-House Fan
In some very specific situations, a whole-house fan may be useful for summer cooling

A.  Yes, it could work nicely. It’s quite different from having an attic fan in a gable or on the roof for the sole purpose of cooling the attic in summer and removing moisture in winter; that system is what draws heated or cooled air from the living quarters because there is seldom enough net free ventilation area (NFVA) in the attic itself to satisfy the CFM requirement (cubic feet per minute) of the fan.

But a fan whose sole purpose is to cool the house at night (with open windows and no AC) during the summer would not have the same deleterious effects. It is best to have it installed in a gable wall, as a fan is more effective drawing air out than pushing it through screened areas.

Be sure to make provisions for effective insulation of the ceiling louvers in other seasons — otherwise you will incur a tremendous heat loss through them. That means that, unless you can work out an effective insulation system from below, you will have to have easy access to the attic, such as a disappearing stairway, which will also need to be effectively insulated. Having to lug a ladder upstairs to climb in the attic through a usually small, difficult-to-access, and hopefully insulated, hatch (referred to as a scuttle hole) often found in a closet is a serious deterrent.

Bubbles appear when toilet is flushed

Q.    Can you tell me why our first floor toilet emits a bubble each time we flush? We are on a slab with a septic system. The vent is not blocked. We are elderly in need of help.

A.    This is usually an indication of a venting problem. If this happens only in winter, it may be that the vent stack through the roof has too small a diameter and ices up. If it happens year around, then the venting problem is different. Does it bother you so much that you can’t live with it? If so, consider having an experienced licensed plumber check it out.

Ridge vents work only with soffit venting

Q. The day after every snowstorm, icicles and ice dams form on my roof. The attic floor is very well insulated, but there are no soffits because there is no roof overhang. There is only one attic vent on the side of the house. Would a ridge vent relieve my ice problem? Any help you can give would be appreciated.

Soffit and Ridge Vents
Air flow through soffit and ridge vents.

A.    Ridge vents are not effective without equivalent, or greater, soffit venting. The ice dams and icicles you experience, in spite of having a very well insulated attic floor, tell you that there is considerable heat loss into the attic through some paths.

Sometimes, the only way to find these anomalies is through infrared thermography and a blow-door test. Call your power company and ask if they perform these tests or can refer you to someone who does. The cost may be significant, but think of the money you will save on energy costs – and in the prevention of costly damages to your house. There may also be a program in your state where the utilities perform these tests at no cost.

Vented Drip Edge
Vented Drip Edge

If your roof will need replacing in the near future, it is possible to have soffit venting installed despite having no overhangs. For instance, Air Vent, Inc. ( manufactures a Vented Drip Edge for just such situations. It requires minor alterations to the roof sheathing.

Other manufacturers also offer such systems. DCI Products ( offer the Smart Vent, which can also be installed where roofs do not have overhangs.

Smart Vent installation diagram
Smart Vent installation diagram

Check with your local building supply stores for availability or order online. Then a ridge vent will make sense. If you decide to go that route, close the gable vent as it will interfere negatively with the new system.

But the energy tests I suggest may help determine whether or not you need more ventilation. If the anomalies are easily fixed with closed-cell foam, you may not need any ventilation, although it is generally considered advisable.

Venting two bathroom fans through a gable wall

Q.   I have two bathroom fans that now exhaust in the attic. The closest gable wall is blocked by a cathedral ceiling and skylight. The other gable wall is 28 and 21 feet away from each fan, respectively.

Is it acceptable to run the plastic drain pipe that distance? Can I run both fans into a single 4-inch pipe? What type of vent would I put on the exterior of the gable wall – something like a dryer vent?

A.  The longer the run, the harder the fan works, but if you have no choice, keep the duct as straight as possible, avoiding bends. Do not run both fans into the same duct, as that often results in recirculation from one bathroom to the other.

I once investigated an apartment building where this had been done; one of the two bathrooms in an adjacent apartment was covered with mildew and mold even though it was not used. Crawling in the attic revealed the connection of four bath fans into one long duct going to a gable vent. The resistance to the airflow in the long duct caused the air to back up in the nearest bathroom, especially when more than one fan was on at the same time.

Bell-End Pipe
Bell-End Pipe

The best way to vent bathroom fans is with Schedule 20, bell-end drain pipe. These pipes come in 10 foot length, and the bell end must face the fan. If possible, place two small wood blocks of diminishing thickness under each section of pipe to encourage drainage of any condensate to the outside. Snug 4-inch thick fiberglass insulation to the pipe on each side and place another layer on top to reduce the risk of freezing of the condensate in a cold attic.

The best wall jacks are hooded aluminum or plastic types; louvered jack have a tendency to break, leaving places for rodents or birds to get in the pipe.

Hooded Wall Jack
Hooded Wall Jack


Water collects inside of windows in winter

Q.   I hope you might be able to shed some insight on a problem I have with my windows. As soon as it gets cold, beginning sometime in October until the weather warms up in the spring, water collects on our windows and forms long puddles along the bases, where the glass meets the wood. We have storm windows as well as new insulated windows but this problem persists.

First thing in the morning, I open my curtains and wipe up the water. Opening the curtains does not solve the problem, but it helps in most of the rooms of my house. Anyway, I fear that my windows will all be rotting soon if I don’t resolve this perplexing problem. Do you have any ideas about what is causing this massive amount of condensation and what I can do to prevent it?

A.    Drawn window shades at night will cause condensation on glass, especially if the shades are of the insulating type. The air trapped between the glass and the shades is cooled, and the dew point is reached.

The fact that you have such a serious condensation problem in spite of having insulated windows and storm windows is an indication that there is too much moisture in your house. If you didn’t have this problem before having new windows put in, it is because the old windows were leaky and allowed greater exchanges of air in the house. The new windows are obviously tighter and the number of air exchanges is greatly reduced.

If you have a warm air system and there is a humidifier on your furnace, and you are using it, I suggest that you shut it off, empty it and clean it with a bleach solution. Make sure that it is dry.

You should also look at your lifestyle and see if there are things you can do to reduce the relative humidity (RH) in the house.

For instance, do you dry laundry on racks inside the house, or is your dryer properly vented to the outside? Do you have lots of water-loving plants? Is your house modest in size with several children and pets? Is your cooking generating a lot of steam, and is it with gas? Does your family take long, hot showers? Store firewood inside?

If there are things you cannot change, you might want to look into an air-to-air heat exchanger.

Getting best value when replacing siding and roofing

Q.    I am soon having my split-level house re-roofed, while also installing new siding and gutters. The enclosed picture (below) shows my home, which faces South.

904 Ironwood

When the contractor strips off the old (original) aluminum siding, he will be injecting Airkrete into the wall cavities all around the house (also the brick). The lower roof on the right (East) side of the house covers a cathedral ceiling which is over the front living room and a few steps up, to the dining room. The far North side of this lower roof covers the kitchen which has a regular 8-foot ceiling.

The contractor will also be injecting the Airkrete into the cathedral ceiling, and adding additional blown-in insulation above the kitchen. There are two can vents over the kitchen area. Airkrete will also be injected into the walls and ceiling in the attached garage.

On the top roof, you can see the front gable vent, there is also a matching gable vent on the North side of the house. There are also four can vents on top of roof. I have a 1500 cfm. powered attic fan on the East side of the top roof.

Fifteen years ago, I re-insulated the attic using Owens Corning R-25  batts (I think it was called Easy Touch. Has a thin sheathing all around the batt). First layer laid in the floor joists, 2nd layer laid perpendicular over 1st layer.  I also installed soffit vent chutes in all rafters at the soffit area.

For the siding, my contractor will be installing Mastic Structure foam-backed Dutch lap siding over Tyvek housewrap. For the roof, he will be installing GAF Timberline Architectural shingles with 6 feet of ice and snow shield.  The 4-inch gutters will be replaced with 6-inch gutters and downspouts. The wood railing and posts above the garage will be replaced with Azek board material.

I would greatly appreciate your opinion and suggestions to make sure this is being done correctly so I can get the most value for the money I am investing in this major renovation. My location is a Northwest suburb of Chicago. Thank you.

A.    Everything you are having done seems fine. The only comments I would offer are as follows:

  • Power roof vents have serious drawbacks. Unless there is enough net, free ventilation area (NFVA) in the attic itself to satisfy their CFM rating – which is seldom the case – they will draw conditioned air from below. This is a waste of energy both summer (assuming that you have central air-conditioning) and winter.
  • A better approach is to insulate the attic as you did, and make sure that you have adequate passive ventilation by means of continuous soffit and externally-baffled ridge vents. You also must have an uninterrupted air flow between the soffits and the ridge.
  • However, if there are no moisture problems in the attic, it would indicate that the two gable vents are doing the job, in which case there is no need to change anything.
  • Roof can vents are not effective, and it is best to eliminate them in favor of the passive ventilation described above. But, as mentioned above, if you have no problem, don’t change anything.

Otherwise, you are doing fine. I am glad that you are replacing residential gutters and downspouts with commercial ones; it’s a winning combination.

One toilet gurgles when another is flushed

Q.    We have a 50-plus year-old Cape Cod home with a powder room on the first floor and a full bathroom on the second floor. For the last several years, when the toilet on the second floor is flushed, water gurgles up in the bowl of the toilet in the first floor powder room. What could be causing this? Do we have reason to be concerned? If so, how should we proceed?

A.    Such gurgling sounds are usually caused by a venting problem. The vent stack that goes through the roof (or should, if yours does not) may have gotten partially or totally plugged over the years. This is more of a problem in very cold regions where the moist gases freeze over the winter and can cause the vent stack to be completely closed.

If this problem is year around, it may be that the vent stack has a small diameter and that a build-up of scum and corrosion has narrowed it to the point where it is affecting its proper functioning. You may want to have a plumbing contractor get on the roof and check it out; it may need to be cleaned out. He or she should also check for other possible causes, such as absence of venting, which may be remedied with interior venting, using one of the several appliances available.

Bathroom stays wet despite exhaust fan

Q.  Every time we take a shower, the walls just get very wet and sometimes the water runs down the walls. We have a very good ceiling fan. We are at our wits end, what could be causing this problem? Any advice would be greatly appreciated.

A.    Have you checked that the fan exhausts outside through a gable wall? And that the outlet is not blocked? If the fan exhausts in the attic itself, or through a soffit, gable or ridge vent, it is not doing its job and you should have that taken care of. Your family may also be taking some long or very hot showers; that will overwhelm the ability of the fan to keep up with the moisture generated by the showers.