My client has a Spark linear natural gas burner system, rated at 129,000 BTU/HR, which is open on three sides to the room. There is an exhaust hood above the burner with 3 variable speed Enervex roof mounted fans, and the equivalent of more than four 4 inch diameter ducts bringing in outside air beneath the Spark system per the manufacturer recommendations. The controller board failed some time ago and all three fans were running full speed creating an obnoxious amount of noise in the room. Now that we have replaced the board we can set the fan speed at any rate that we need. The question is how do we calculate the minimum CFM that we should be exhausting? The construction of the home is very tight.
Calculating Required CFM Exhaust for Open Fireplace
- Thread starter Craig Cernek
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Call the manufacturer they are the only ones that can say
The fireplace manufacturer's reply.
"The required CFM for exhaust is not based on the product but based on the opening of the fireplace and the height and size of the available flue. The Btu's of the appliance are not a factor, it is all about air movement to assure draw through the chimney.
Enervex are the experts on this and can calculate what the fan should be to provide proper draft based on these parameters and the fan controls are variable to prove draft but reduce noise if draft is proven.
The lower the hood and the less open area will allow for less draw required. Outside air to the base of the structure can help draft instead of using room air. "
"The required CFM for exhaust is not based on the product but based on the opening of the fireplace and the height and size of the available flue. The Btu's of the appliance are not a factor, it is all about air movement to assure draw through the chimney.
Enervex are the experts on this and can calculate what the fan should be to provide proper draft based on these parameters and the fan controls are variable to prove draft but reduce noise if draft is proven.
The lower the hood and the less open area will allow for less draw required. Outside air to the base of the structure can help draft instead of using room air. "
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