February 2, 2002
Our subject for this week was a request from one of our readers who asked the following:
Could you elaborate on Dryers, back drafting of water heaters and furnaces leading to flue gases and carbon monoxide entering the home? I have an electric dryer I have just bought and the only place for it is in the basement near the oil fired furnace.
In August I covered a subject titled "Will Your Dryer Kill
You?" (click on it if you want to check it out). I guess we will need to title this one:
Will Your Dryer Cause Your Furnace To Kill You?
Remember sitting in your grandmothers home and her saying: "There is a draft in here." What was she talking about? There was air moving in the room causing a chill. The air in a home is constantly moving. This movement is caused by many different things such as convection (hot air moving toward cold), openings in the home (windows, doors, fireplaces), mechanical vents such as bathroom fans, kitchen exhaust fans, attic vent fans, dryer vents, to mention a few. Heat from combustion causes air to rise. Standing outside facing a roaring fire, you can visually observe the smoke rising into the air from the heat of the fire. If its really cold you can stand close to the fire and your front will become too hot while your rear will be freezing. This is because the fire is drawing the cold air by you to replace the hot air which is rising into the air. So we turn around and our rear becomes too warm while our front freezes. This air movement or DRAFT is what makes an open fire or a vented fireplace so inefficient at providing reasonable comfortable heat.
Furnace and water heater flues make use of the natural act of hot air rising toward cold to draw combustion gases out of your home. As the burner heats, air rises through the flue drawing the gases out of the home. Now you are thinking, "CHRIS, what do you think we are dummies?" You knew all of that, didn't you?
Sorry, but I had so set the stage for the main subject which we don't know so much about. Sure, hot air rises, but what we tend to forget is that when it rises, it must be replaced with air from somewhere. Henceforth comes the issue at hand. Where does this replacement air come from? Well, most of the time it is coming from within your home and then being replaced from the outside sucked though every hole, crack and opening in your home. The tighter the home is constructed the more difficult is to replace this air moving out your flues. Aren't we trying to build homes tighter all of the time? Sure we are, we don't want that cold air coming in to have to be heated ($$$) or to feel it moving past our feet freezing our toes. The problem that is caused by our efforts to build tighter and tighter homes is that mechanical systems which must draw replacement air to function such as furnaces, water heaters, dryers, vent fans and such are constantly in competition for the available make-up air. This is why many systems are going to sealed combustion chambers, powered venting and piped make-up air.
What makes all of this even worse is that all of these systems are installed by different contractors and no one is making any effort to check and balance the overall demand for this air. The mechanical contractor installs the furnace, plumber the water heater, electrician the exhaust fans and then after you move in your appliance person brings in a dryer. Does anyone make an effort to determine if there is enough air available for the demand of all of these systems running at the same time? Almost never. Guess what happens when there is not enough air. It must come from somewhere and the easiest place is from the furnace, water heater and fireplace flue pipe. Now you know why that fireplace will not draw. If this occurs while these units are operating, guess what comes along with it. Combustion gases, one of which is carbon monoxide, bringing headaches, dizziness, nausea, sickness, and possibly DEATH. And you thought you had the flu. Be aware that flu type symptoms don't last over and extended period of time. If you appear to be sick for an extended period of time you should check for possible backdrafting and high carbon monoxide.
Making this even more complicated is that the weather, barometric pressure, wind, what doors or windows you may have open or closed, the fact that your attic vent fan comes on and you don't even know it can throw all of this out of balance. There are ways to calculate the adequacy and proper operation of this, but it is complicated and ALL issues must be considered. Does it happen? Hardly ever. Ideally you want your home to be under positive pressure. What this means is under regular operating conditions with the doors and window closed, the air inside of your home should be moving out the cracks and holes which are in all of our homes. Under this condition flue gases will always move out of the home. Throw off the balance by the addition of a dryer in a small enclosed room along with a gas or oil furnace and water heater, fail to consider adequate make-up air, and you are asking for trouble. Do you want to make your family sick? I don't think so. Then you must pay attention to the air movement in your home. The air must go out those flues under all conditions with every type of demand for air in your home considered.
In plan simple southern English: Add a dryer in an enclosed space along with the existing gas or oil furnace and water heater and be prepared to be sick or for your relatives to walk in one morning and find you dead.
This is what home inspections are all about, unfortunately it is difficult, if not impossible, for a home inspector to know that a problem exists except for the tell tell signs of lack of adequate ventilation or poor draft. You should be aware, as should your clients, that just because your home has been inspected by the best home inspector in town doesn't mean that you don't or will not at some point experience a back drafting problem. Being totally comfortable with this issues involves much more than the average home inspection.
Pam (my lovely Realtor bride) read this article and complained that I left you hanging, not telling you what to do or who to call. I tried to explain that it's not a home inspectors responsibility to deal with what to do or who to call, only to observe and report the problem. But. she was persistent, so here is a link to a Internet site where you can download a PDF file from the Minnesota Department of Commerce Energy Information Center on the subject. Maybe now she will be quiet. Click here:
Air" or go to this site:
(you must have Acrobat Reader to read it, if you don't have it, you can get it free at
Bonus (we have talked about this before): Had a call this week involving problems with polybutylene water pipe. A good web site for detailed information about this is
"www.plumbing911.com." (Clicking here should take you there.) I am not endorsing this site or the company by any means, but if you need to become informed this is a good place to start.
Thought for the week
"Sex is like air. It's not important unless you aren't getting any."