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.

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.

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.

Mold in the window casings of a tight house

Q.    We built our home and have lived in it for 4 years now. The contractor is very environmentally minded and created an exceptionally tight house. It seems that during the colder months, we develop mold on the wood casings of our windows during the nights, especially the ones with blinds or shades.

We’re very concerned about the “rot-factor”, and, more importantly, the baby seems to have developed an allergy to the mold. Can you let us know how we can cure this problem, regarding both air-quality and wood preservation?

A.    The blinds and shades trap ambient moist air between the blinds and the windows. During the night, this air cools and its relative humidity increases to the point where it encourages mold growth.

You could leave the shades and blinds up to see if this solves the problem. But it sounds as if you need an air-to-air heat exchanger. This can be a whole-house system or one or more individual room units, depending on your house design.

Improving ventilation when re-roofing

Q.    In reading over your articles, you seem to be opposed to any kind of attic fan or roof venting fan as costly and ineffective for cooling off the rooms below.

Our roof’s shingles are over 20 years old and it would seem an opportune time to have an attic fan mounted that vents through the roof. If you feel this is an ineffective and costly solution, what do you recommend at this time since we’re considering having our shingles redone to help cool off the rooms below?

A.    Research has demonstrated that attic fans are seldom getting the replacement air they need from the attic itself. So they draw air from the conditioned living areas, robbing heated air from the house in winter and air-conditioned air in summer. That is why they are not considered the best way to go.

The best attic venting system is one consisting of continuous soffit vents (not a few holes here and there) and a continuous (also called “running”) externally baffled ridge vent. There must also be an uninterrupted air space a minimum of 1-1/2 inches above the insulation between the soffits and the ridge. Be sure that the selected ridge vent is externally baffled, such as Shinglevent II; unfortunately, most ridge-venting systems sold are not. With an externally baffled ridge vent, the wind is deflected over the vent. The result is an internal suction of the attic’s air through the soffit and the ridge vents, thus increasing its effectiveness — the Bernoulli Principle.

Non-externally baffled ridge vents are ineffective in windy conditions, as the wind stops the exhausting of air through the ridge vent, which effectively stops the intake from the soffit vents — and they can get clogged with snow or admit it and rain.

The best way to increase the comfort in the bedrooms below the attic is to increase the level of insulation in the attic; it helps as much in summer as it does in winter. An additional way is to have light colored shingles installed.