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  • Writer's picturePhoenix Heating & Air

Ventilation, your fuel burning heating system needs to breathe.

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Ventilation, it’s just like breathing!

Ventilation can mean many things, air surrounding the unit, cold air returns, heated air going from your system to the house through vents, or the bad air ventilation going out from your oil, gas or propane heating system to the outdoors through the flue. Your system breathes similar you how you breathe, air goes in and comes out, but we call it ventilation.

What can you do if you are using a fuel powered heating system to heat your home to stay safe?

The very first and most important thing is, have working carbon monoxide and gas alarms in the right places, that are tested monthly, and have good batteries in them to keep yourself safe from unsafe gasses and emissions from your heating system, gas appliances, or gas connections in your home. If you are hearing impaired, here is a great resource for you: Hard of Hearing assistive alerting devices ( Also, in case of fire or gas leak, have an emergency evacuation plan and do regular fire drills so that everyone can get outside in an emergency.

furnace with breathing room

Breathing in: surrounding furnace air & cold air returns

For your fuel heating system to start, ventilation coming in is essential. Keeping the intake grate or openings on your furnace and boiler and cold air returns unobstructed is one of the easiest things you can do to ensure safety of your heating system. The air must flow freely into and out of your heating system from cold air returns and the air surrounding the furnace. Your furnace needs oxygen to breathe just like you do, except it uses oxygen to produce a flame during combustion.

Some of the newer high efficiency heating systems need even more fresh air than older systems to run at peak performance. If your system is struggling to pull in the air it needs, it is putting excess pressure on the system. This includes dirty air intake filters blocking air flow, so changing them regularly is very important.

change air fiters regularly

This excess pressure causes less fuel efficiency and eventually leads to failure of the system. It costs more to run your system and can cause internal damage to your system, such as cracked heat exchangers, which are very dangerous causing raw gasses and Carbon Monoxide to enter the home.

Leave 10 inches of space

Cold Air returns are essential to your heating and cooling system’s performance whether it is fuel or electric. Hot air rises and cold air falls. Your lower cold air returns, either in the wall or in the floor, are providing the air your furnace or boiler needs to warm and return to the house through the air vents. Covering or blocking these cold air returns causes air pressure issues and your system to struggle to operate.

Generally, for proper air flow leave 10” of space in front of your cold air returns.

Air returns that are near the top of the wall are usually used for an air conditioning system and if you have cold air returns both above and below, you can generally close the upper return vents in the winter to keep the warm air in the room and close the lower return vents in the summer to keep the cool air in the room to maximize your system. Don’t forget to open these up in the proper time. Ask us which vents should be open or closed, if you have any concerns.

keeping air ducts and return ducts clean and unobstructed

Warming the house: ducts and air vents

Your ductwork was most likely sized properly for the size of your heating system. Decreasing the number of available vents should only be determined by qualified technicians to make sure there are no backpressure issues in the system. Re-routing of vents should also be done by qualified technicians to make sure there is proper airflow in every room. If a vent is blocked by furniture, there are vent extenders that can be used to bring the air to the front of the piece of furniture.

If you have heating or cold air intake vents that are unsightly, there are decorative covers available in stores, just please don’t block the flow of air to these or any vents.

Breathing out: flue ventilation, or exhaust

Ventilation going out of your fuel heating system, exhaust, through a flue is toxic. You don’t want it inside your house, so it is vented outdoors to dissipate. That is why an unobstructed flue is necessary. Don’t cover your flue up with flowers outside or decorations that may block the airflow. It is not a good place to anchor your rooftop Santa or hang your snow melt cables from.

make sure your flue is clear and unobstructed

Your flue can, in the worst situation, also emit flammable unburnt gasses if your system is running too rich. If your flue is blocked or obstructed by anything, including a bird or animal nest, please do not run your heating system until it is cleared. Running your heating system with a blocked flue is dangerous to property and life.

If your flue is damaged or the pipe that is exhausting the fumes out through the flue is damaged or missing, get it repaired before running your heating system further to keep from having dangerous gasses enter your home. Blocking the flow out of your system is not good, as it can cause backpressure within the system, and leak gasses inside the home because they have nowhere else to go. Call us immediately if your flue is damaged, missing or blocked, so we can get your system running safely so you can use it again.

Backdraft, (if you haven't seen the movie, that’s fine; this is about furnaces) n simple terms, is where the system loses pressure which stops the outgoing air, and it comes back inside where it doesn’t belong. If you are having a backdraft issue, you need that inspected and repaired right away to be safe.

Creating a safe space around the furnace

be safe and keep things away from your furnace and don't put flammable objects on or near

Another very important safety matter is to not put anything that could cause fire or explosion near, on or against your heating system. Please leave the empty space that the manufacturer recommends around your unit. It is not a good place to store papers, boxes, furniture, curtains, paint, paint thinners, chemicals, rags, cleaning supplies, pool treatments, hairspray, or anything else that is flammable near your furnace or boiler. Intense heat can be generated from your system including vents. Try to keep all airflow unrestricted. If airflow to or from the furnace is blocked, and if something gets too close, it can ignite, causing a fire. This also applies to electric furnaces.

Get your furnace maintenance done to keep it running efficiently and safely

Lastly, an important thing you can do that may be the easiest of all: call, text or fill out this online request for a boiler or furnace maintenance visit.

We have professional technicians trained in combustion safety to make sure your system is running with peak performance and safety. We also test airflow during maintenance visits.

Stay tuned for next time, when we discuss Boiler Safety. Take care!

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