What is Draft?

  January 1, 2014      Jeff Rosenblum


Very often you may be asked to check or verify draft. So what exactly is draft and what does it do? Draft is the chimney’s ability to draw the burnt gasses out of the furnace. Newer high efficiency furnaces don’t have to worry about this but anything that is natural draft or uses the chimney for exhaust should verify proper draft. Typically a proper draft would be around .01-.02”wc (water column) but consult your owner’s manual for the correct amount.

Now that we know what draft is, how do we check it? The easiest way to check draft is to drill a small hole in the flue about 18” away from the furnace in a straight piece of pipe and insert a draft gauge. Some draft gauges use a little Styrofoam ball while others are digital and some use a needle. Once finished checking the draft, make sure you plug the hole in the flue.

So what can affect draft? There are sev­eral factors that can contribute to a low or high draft. The height of the chimney, size of the crock, temperature of the flue, outside temperature, pressure or nega­tive pressure of the house all play a criti­cal role in affecting the draft.

If you have any questions regarding draft please feel free to contact the HVAC Tech Support Team for assistance.

Jeff Rosenblum 
Technical Support
15 Years Industry Experience
Cell (330) 962-2491
[email protected]