Carbon Monoxide, and Naps

It may not be the Turkey that makes you sleepy.

Carbon monoxide from an electric oven

Cooking the turkey for hours can introduce considerable amounts of carbon monoxide to the home during the cooking process.  Turkey has a component that has been attributed to that nap after dinner.  Others hypothesize it is just eating too much that leads to sleepiness.  It is also possible that exposure to Carbon Monoxide is a contributor.

If carbon monoxide is a culprit, it is not only related to gas ovens. 

I am not sure how much CO is given off in an electric oven during the cooking of a turkey, but certainly some amount is likely. I will have to wait until Thanksgiving to get more information on that.

Considerable is created when using the self-clean function of the oven. 

My own oven gives off between 28 and 3 PPM for the first 1-1/2 hours of the 3 hour cycle.  After that time, whatever was creating the CO was successfully incinerated and CO levels dropped to normal. 

These amounts are perhaps not enough to kill you, but certainly enough to affect a person–especially infants that might be around.

In the first 15 minutes of operation, my own oven gave off about 28 PPM, after about half an hour it settled down to 12 PPM and after about an hour it was down to 5 PPM.  At the one-hour mark, ambient CO levels in the kitchen 10 feet away from the oven hovered around 3 PPM—with the exhaust fan on and a window open.

I suspect the amount of CO will depend on what the oven is burning off in the cleaning mode, and levels likely could be considerably higher, and for longer periods of time, if the oven is not cleaned very often.  I clean min probably twice a year.  I may start doing it more often now.

Of course your ordinary CO alarm is “not allowed” to alarm, per its listing, at these low levels, so most of the time you will have no idea why you need a nap.

I think the lesson here is to clean your ovens regularly–don’t wait until you can see the bottom of the oven.  You should also run the kitchen exhaust hood the whole cleaning cycle and keep a window open.

Perhaps I will go take a nap, while I wait for the oven to finish.

Charles Buell, real estate inspections in Seattle

Stack Effect does not need help!

Stack effect does its best to create a river of air through your house–it wants to flow in at the bottom and out the top.

Stack effect is the movement of air into and out of buildings, chimneys, flue-gas stacks, or other containers, resulting from air buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect helps drive natural ventilation, air infiltration, and fires. 

Our air sealing efforts can mitigate stack effect but it is always ready flow as soon as there is an opening.

While houses that have less than 1ACH-50 (air changes per hour) come close to combating stack effect, current energy code requirements of 3ACH-50, does not. (Washington State Energy Code is still stuck on 5ACH-50–likely until the 2021 Code Cycle.) 

For this post we will be talking about homes that meet current energy code requirements—or are worse than current code requirements.

In modern tight construction, for exhaust fans to function and to change air in the home, we must also provide a path for fresh air to enter the home when the fans are running.  Sometimes the air intake locations are with vents built into the vinyl windows themselves.  I do not want to discuss all the other means of providing fresh air to the home.  This post will only focus on the window air intake type vents.

There are problems with these air intakes in multi-story homes.  When the vents are open, they allow that river of air to flow 24/7.  In my experience, these vents are either always open or always closed because the homeowner does not know what to do with them.  Just as often they do not even know they are there.  The result is WAY more air changes per hour than the house was constructed to meet.

In the following pictures we can see the result of stack effect on vinyl windows with the window vents open. 

Air Intake

The windows are covered with plastic related to painting the building.  Notice how the plastic puffs out at the top and sucks in at the bottom–clearly demonstrating the power of stack effect.

Stack Effect

Stack Effect

Solutions to this issue are illusive, but there certainly should not be any vents up high. If there are, they should be kept closed.  At 3ACH-50 there will always be enough air leakage to change the air more-or-less continually at the upper level–but obviously this is not the desired way to do it.  Leaving the vents open at the bottom level to allow for fresh air intake when exhaust fans or the whole house air exchange fans are running should be sufficient.

Abandonment of window intake type vents in favor of barometric type intakes would be a far better option.

We certainly cannot allow the river of air to flow wild.

A while back I did another post  about how when these vents are left open at both levels it can result in too low of an indoor humidity.  The window intakes can allow us to lose control of the indoor environment when some become outlets.

Charles Buell,

Real Estate Inspections in Seattle

Do your exhaust vents terminate at your soffits?

The building codes specify that exhaust fans shall not terminate in the attic or soffits. While there are those that argue “at the soffits” is not the same as “through the soffits,” I think it pretty much amounts to the same thing.

The reasons we do not want to vent warm moist air into attics is well known and documented. It can lead to mold growth and other four letter words.

So what exactly does the code say:

M1501.1 Outdoor discharge. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.

That seems straightforward enough, and since “aimed at the soffit” is still in the attic, my personal opinion is, when the code says “Shall not be exhausted into a …..soffit,” they are meaning “through the soffit” as well.

So let’s forget about the code, and let’s see if my opinion can be supported by building science.

Wow, do we really have to go to “science?”

What are the building conditions that would come into play to sort this all out? Typically, or at least most of the time, in a properly vented attic, the attic space is under negative pressure relative to the higher pressures at the soffits and at the ridge. Because of this, air is attempting to push its way into the negative air space to make balance–24/7. All air in the vicinity of the soffit vents is forcing its way into the vents.

Now lets place a bathroom exhaust fan vent right at the soffit vents.

We are exhausting warm, wet, buoyant air that it is already moving upward and increasing the pressure in the area of the soffits. This increase in pressure difference between the attic space and the soffits makes that warm wet air work even harder to get into the attic.

In this picture, you can see evidence of where corrections have been made of the four vents that terminated too close to the soffit. The opening have been covered over, and hopefully they now terminate properly through the roof.

The staining on the siding above the lower vents is consistent with the buoyancy of the air from the vents.

Staining above the soffit vents on the underside of the roof sheathing is consistent with the upper vent’s previous termination at the soffits.

I think the codes need to clean this up a bit and require minimum distances to vented soffits.  Any current guidelines are at best “vague.”

Until then we should resort to good sense.

Charles Buell, Real Estate Inspections in Seattle