Introducing fresh air to a building envelope for ventilation, adds to the heating and cooling loads. At first this may appear to be at cross purposes with the air tightening process which reduces heating and cooling loads, but mechanical fresh air introduction is controlled at a level sufficient for the health of the occupants and the health of the structure. Air infiltration is no longer random and erratic in volume or behaviour.

Overall, the amount of outside air entering the structure is reduced by using mechanical ventilation, but the amount of energy required to condition the fresh air is still significant.

The formula below calculates the amount of heat necessary to warm 180 cfm. of fresh outside air, from 0° F. to 72° F. on a peak winter day in Toronto, in January traditionally the coldest month. 180 cfm. could easily represent the ventilation requirements of a typical 3 or 4 bedroom home as mandated by the OBC.

E.g. 180 cfm x 72° F x 1.08 = 13,997 Btuh.

The building must exhaust 180 cfm. of warm air, to allow 180 cfm. of fresh air to enter the building without affecting the internal air pressure of the building in either a positive or negative manner.

Fig 4. Typical HRV Construction

An HRV as shown in Fig 4. captures the heat available from the exhaust air and transfers a good deal of it, (60% to 70%), to the incoming fresh air. Therefore only the balance of 30% to 40% of the heat is required to bring the fresh air up to 72° F.

A further benefit of an HRV is the fresh air temperature entering the home is a good deal warmer than if it was not preheated. As the ventilation air is mixed into the return air of the furnace for delivery around the house, the air temperature leaving the furnace at the plenum is also warmer.

Geothermal Furnaces recommend the use of a Heat Recovery Ventilator,

Lifebreath HRV

(HRV) for controlled mechanical ventilation. We employ heat recovery from stale exhaust to the homeowners advantage using primarily Lifebreath HRV equipment.

The HRV minimizes unwanted air and moisture movement through the structural envelop and allows the intake and cleansing of the correct amount of fresh air for your home.

Air tight construction does come with some controversy attached to it. High humidity levels have occurred in very tight, under ventilated buildings. Failures in air tight homes have all been due due to inadequate ventilation and are therefore preventable. As the saying goes "Build Tight and Ventilate Right".

Geo-Thermal Furnaces Ltd. does not insist that customers build air tight. We know from experience however, that properly implemented, air tight homes stand out in energy performance and are the most comfortable and quiet. Talking with builders who have had good experiences with or even specialize in this type of home construction should prove worthwhile to the homeowner.

And don't worry, Geothermal Furnaces will get the ventilation part right.

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