Keep your vents clear – it could save your life


The snow has been in the news a whole lot lately and we’ve talked about preparing for the more arduous aspects of a New England winter. But there are some very important things that should be done after the storm. None more so than clearing snow away from your systems’ vents.

Whether you heat with oil or gas, your system has an exhaust pipe. And many systems have an air-intake pipe. All of these pipes begin or end somewhere outside the building. In older systems the exhaust will often be led up a chimney, significantly reducing the possibility of being blocked by snow or other debris, but in newer houses the pipes typically go through exterior walls and more often than not vent through the sill – the perfect location for snow build up. But what do these vents and pipes do, and why is it important to keep them clear?


A furnace or boiler needs three things to work: fuel, oxygen, and a spark. In older houses the boiler or furnace is located in a large basement and will get all the oxygen it needs from the air in its immediate vicinity. But in newer well-insulated and ‘tight’ buildings heating systems are fitted into increasingly small spaces with insufficient combustion air, and therefore oxygen, to feed the system – thus, the boiler or furnace needs an air-intake pipe from the outside of the property.

Once fuel, oxygen, and a spark (for ignition) are provided, the system will fire up and produce two things: heat and carbon monoxide (CO). The first is desirable – indeed it’s why we have the system in the first place! But the second, the carbon monoxide, is poisonous to humans and so is expelled through an exhaust pipe into the outside world where it dissipates.

If either the air-intake or the exhaust vent becomes blocked – by snow for instance – the system will stall, either because it will be starved of oxygen, or because its built-in safety mechanism will shut it off. If the blockage is in the air intake the system will shut down, and the property will cool down until the blockage is removed and the system can be re-fired. But if the exhaust vent is covered by snow, the problem can be more worrying. The blockage might be enough to cause the system to shut down, but before that happens a snow ‘cave’ can be formed around the vent trapping the exhaust fumes – including the CO – and forcing them back into the property through cracks in the building itself. CO is odorless, colorless, and tasteless, but in sufficient concentration can be harmful to people and animals. For this reason – and because you really don’t want your heating system to fail in the depths of winter – it is vitally important to keep your exhaust vent clear.

If you don’t know where your system vents, the easiest way to find out is to look at the boiler or furnace. If it’s an older system venting to the chimney, you’ll see an aluminum pipe coming off the back of the furnace. If it’s a newer system, there’ll be two 3”-diameter PVC pipes coming off the top – one’s the air-intake, the other the exhaust – follow those pipes and you’ll see where they exit the building.

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Once you’ve found your vents it’s a good idea to mark their location outside so that if they do become buried in a snow storm you can easily find them. You can even create a simple plywood A-frame over each vent to protect them from less significant snowfall – but nothing’s going to keep them clear from a 21/2-footer like we had last week! Then the only solution is to get out there the next day and start shoveling!

And don’t forget… if you have a static generator it, too, has an air-intake vent so it’s a good idea to clear the snow all around the generator so that it’ll fire when you need it to!

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