A Healthy Draft: Why Your Energy Efficient House Needs A Fresh Air Intake Vent

Posted on: 19 May 2015

Homeowners seeking lower energy bills often go to great lengths hunting down every crack and gap around the structure to keep their heated or cooled air in. However, this can backfire and cause numerous problems if you have any kind of combustion device in the home like a gas-fired furnace, fireplace, or wood stove. Learn how installing a fresh air intake vent, or allowing an HVAC professional to install one, makes an airtight home a lot safer without ruining the effect of a sealed building envelope.

The Back Draft Problem

Every type of combustion, from a tiny campfire to a high efficiency furnace, requires a surprising amount of oxygen to stay burning. The fire can (and will) use up all the free oxygen in your house unless it gets a convenient source of fresh air from outside the home. In an older house with plenty of leaks, the draw leads to air coming in through the gaps for a safe flow. It's ironic, but a home with no leaks actually becomes less safe than an older design unless you compensate for the changes.

New and renovated houses with a tight design don't let much air leak in at all. This raises the pressure inside the house as the air gets used up, leading to air being drawn back out of vents and chimneys. The effect is known as back drafting. For example, your furnace might suck fumes back out of a fireplace and create a dangerous increase in the amount of carbon monoxide with little warning.

Moisture Development

A lack of fresh air also increases the amount of moisture trapped inside the house, especially when you combine an improved building envelope with a high efficiency modern furnace. Installing a vent for fresh air encourages the damp indoor air to blow up into chimneys and vents for different appliances. Giving your home an extra source of incoming air increases the drawing power of stove hoods, bathroom exhaust fans, and attic fans to process the extra moisture in the air during the winter.

Installing the Vent

If you're concerned about letting in hot or cold air through an intake like this, consider installing the opening right next to the combustion appliance so the air is used up quickly. Many furnaces, wood stoves, and fireplace inserts also come with their own connected pipes for bringing fresh air directly into the firebox. There's no need to place a vent far away from the appliance using it, but you do need a few feet between a vent for smoke or fumes and the fresh air source to prevent contamination.