While there are so many wonderful things about technology and the improvements that have allowed us to build more efficient, airtight homes, it’s caused a dangerous problem that can be easily overlooked.
Modern houses are really quite amazing structures. They are made up entirely of systems that interact with each other on a daily basis without the average person even being aware of it. Thousands of hours have been poured into research and production of each system, and all of this goes, for the most part, unnoticed by the occupant.
With changing technology, comes new and different safety concerns. One’s that could put your family and loved ones at risk, should they be neglected.
Homes over the years have gradually become more and more airtight. While this is fantastic when it comes to heating and cooling efficiencies, it poses an oftentimes overlooked threat:
What is backdrafting? Backdrafting occurs when a house is put into “negative pressure”. In simple terms, what this means, is that the house is essentially consuming more air than it’s receiving. This creates a sort of vacuum, which will use whatever source of air comes the easiest. unless you leave a door or window open during the Winter (not likely in Idaho), then that “easiest” source will probably be the exhaust vents, chimneys, and flues.
Now imagine what would happen when you fire up the furnace, or any other gas, oil, or solid fuel appliance with a flue? You guessed it; the combustion products would backdraft into the home, creating dangerous amounts of carbon monoxide (due to improper combustion) and hazardous gases. Now, if this all happened while you were asleep, then you may not even notice that this was occurring until it was too late.
With older homes that are less airtight than more recent construction homes, this becomes a little less of an issue (though it can still be an issue, especially if the home has been renovated or air sealed), as air can be pulled in through cavities in walls and other vulnerable areas.
So, we now know what can increase the risk of negative pressure, but what are some of its underlying causes? Well, usually it has something to do with a fuel burning appliance such as a furnace or a water heater (or both). In order to create a flame, these appliances use up oxygen in the air around it, but if (say) the furnace and water heater are located in an airtight section of the home, then this could force air to be drawn from the easiest source available, i.e., the flue. Since the flues main occupant is the combustion product of the appliance, then this gets sucked into the home as well.
One other contributing factor could be the excessive use of bathroom, kitchen, and laundry room exhaust fans. While these devices are important in pulling stale, humid air out of the house; they do not provide a way for air to get back in while in use.
Now, having said all this, there have been reasonable precautions taken by many manufactures and builders of homes and appliances to prevent this “negative pressure” from happening. Some of which includes the following:
- Backup combustion air flaps installed in tightly built homes near fuel burning appliances, allowing air in to prevent negative pressure.
- Appliances that draw combustion air directly from outside (many times through a PVC pipe).
- Fresh, outside air, supplied and mixed in with inside air via ducts to the air handler, creating a more balanced, or sometimes positive pressure environment in the home. This only works, however, if the blower is running.
- Heat recovery ventilators (HRVs), and other mechanical ventilators which can help even out pressure between the outside air, and inside air.
These are just some of the things that have been developed in whole or part, to help aid in preventing backdrafting in the home. These precautions, however, are usually unbeknownst to the home owner, and sometimes the contractors who install such appliances. It is very important to have these concerns looked at by a professional in the heating industry. They will be able to performs tests on all your appliances and flues in order to understand if this will be an issue or not.
If you are do-it-yourselfer when it comes to many things around the home, it is important to be aware that many things affect other components of the home, and you may consider having a professional walk you through the installation process, and then inspect it upon completion.
All this said, is it bad to have a tightly built home? Absolutely not! Tightly built homes are very efficient, but you must look at the home as a series of interdependant systems, not separate systems. The minute you start separating systems without looking at the ramifications on other systems in the home, you put the occupants and systems at risk.