Q&A / 

Fresh-Air or Make Up Air Intake Vents

Make Up Air is the same thing as Fresh Air Intake. Keep reading.

DEAR TIM: I've got both a fireplace and a free-standing wood heater spaced 15 feet apart from one another in my open kitchen and living area. The fireplace has a fresh air vent in the hearth. I've only used the fireplace twice in fifteen years because when I start a fire in the fireplace, it pulls a sooty smell from the wood heater. Surprisingly, I do not get the smell when I use the wood heater. I'd like to install gas logs in the fireplace. Will gas logs pull air from the wood heater and cause the same sooty smell? Jamie L., Gulfport, MS

DEAR JAMIE: I would be willing to bet money on my answer: Yes. Based upon your description, you are experiencing back drafting. When the fireplace is burning, it is consuming vast amounts of air each minute. It can easily be 250 to 350 cubic feet of air per minute. The fresh air vent in the hearth may be blocked or it may not be able to supply enough air to satisfy the appetite of the fire. The additional air to feed the fire must come from somewhere. Simple physics will tell you that the air will enter the room through the path of least resistance. In your case, it appears the air has decided to enter the room through the flue of the wood heater.

Back drafting is an enormous problem. It is a by-product of the constant push to make homes more energy efficient and air tight. The trouble is, homes are equipped with things that blast air, and lots of it, out of the living space. Have you ever stopped to think about what happens when you activate the switch for your bath fans, kitchen cooking ventilation fans and central vacuum cleaner? What happens when you turn on your clothes dryer? These devices exhaust air outdoors and in doing so create a partial vacuum in your home.

If you do not have an air inlet to re-supply the exhausted air, the replacement air will leak in through windows, doors, chimneys, water heater and furnace exhaust piping, cracks in the house exterior, etc. If several appliances are operating and the demand for air is great enough, exhaust gases from fuel burning appliances can be sucked backwards into your home. This can cause dangerous carbon monoxide to be pulled back into your home.

Many modern furnaces and water heaters have built-in pathways for the air needed to burn the fuel. In fact, virtually every residential building code mandates that combustion air for fuel burning appliances be supplied to fuel-burning appliances. But more air than combustion air is needed in the average home. For years, commercial and institutional building codes have required this extra ventilation or make-up air. This air creates a healthier interior environment, insures that plenty of fresh air is entering the building and that dangerous back drafts are avoided. It is in your best interest to provide this ventilation or make-up air.

This thinking is not new by any means. There are companies that actually sell sophisticated air exchange devices that provide some or all of this needed ventilation or make-up air. But I am not so sure that you need to invest in this equipment. If you do decide to investigate these appliances, be absolutely certain that you see a clear rate of return on your investment. In my opinion, there may be some more practical and far less-expensive solutions.

One device I have seen is very ingenious. It looks similar to a dryer exhaust hood, only larger. Instead of having one pipe feed into this hood, there are two four-inch diameter pipes that connect side-by-side to this fresh air vent. One of the pipes connects directly to the cold air return duct of your forced air heating and cooling system. When your furnace or air conditioner operates, fresh air is pulled into your home. The other four-inch pipe serves as a primary or auxiliary combustion air supply. This pipe terminates near your fuel burning appliances. In your particular case, you could possibly terminate this pipe very close to your fireplace to provide the necessary added combustion air.

Click here to watch the video on these air vents.

You may wonder if the introduction of cold or hot air into your home will cause your energy bills to rise significantly. In actuality, they may stay the same or drop. The air that is consumed by the fans, clothes dryers, vacuums, fireplaces, fuel burning appliances, etc. is coming in anyway to offset the vacuum produced when these things operate. By installing a simple device to cause this air to enter in just one place instead of many different places, the thermostat that controls your furnace and air conditioner may actually cycle on fewer times each day.

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8 Responses to Fresh-Air or Make Up Air Intake Vents

  1. I have a hole in the wall to the outside, a small copper pipe to link it to the outside air, I put metal mosquito mesh over to stop spider, mouse to come in, but it works as fresh air intake. A plumber wanted $550 to install a fresh air intake for the home but my is cheaper and work the same.

  2. We have an vent in our kitchen that acts as an air intake because of our gas air heater. The trouble is that many times there is cold air blowing into our kitchen and house from this vent. Is there a better way to design this?

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