Negative indoor pressure results when more air is leaving your home than is coming in, creating a partial vacuum. In winter, the heated indoor air rises up through the structure and escapes from upper level leaks. At the same time, we force air out of the house with kitchen and bath fans, clothes dryers, furnaces, fireplaces and water heaters, all of which contribute to the negative pressure problem, which is a lack of "make-up air."

Sometimes this can lead to annoying situations, such as a fireplace or stove that leaks smoke (or that won't draw at all). At other times, a more dangerous situation can result, such as a flow reversal in a furnace chimney that spills carbon monoxide into the house. Many building scientists now advise make-up air systems for all new homes, and it is general practice now to require make-up air in new European houses.

Many people ask if ventilating in cold weather isn't an energy wasting practice. The fact is, most heated homes will leak some air due to pressure differences and the natural stack effect of the house. (Stack Effect means your whole house works like a chimney, with heated air rising up the stairways, for example.) If you crack open a window, you will usually feel air coming in to the house rather than blowing out. Without planned ventilation, this negative pressure will suck air in at uncontrolled points.

One way to address this negative pressurization is to ventilate with Condar's ASV-90 Air Supply Ventilator. When you control ventilation, you determine when and where air enters your home, getting the maximum benefit from the least amount of air. While no one product can deal with every house pressure problem, there is an easy test you can perform to check whether the ASV-90 will work for you. Once you've identified a pressure problem, such as a fireplace or stove that won't draw well, try cracking open a window in the room. If that helps the draw, this product will do the job when properly positioned and installed.

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