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Old 11-25-2008, 07:41 AM
Hearthman Hearthman is offline
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Join Date: Nov 2008
Location: Philly
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Cool open hearth efficiency

Rich, you are correct regarding the low efficiency of open hearth Fps. Your typical 36"wide by 30" high fireplace can suck 400-600 cfm up the chimney. Air you already paid to heat. While standing in front of the flames, you will feel heat. This is infrared energy or radiant heat the same as the sun. There is an urban legend this is where the wingbacked chair came from---the breeze of cool air blowing by your glowing face.

Glass doors have been studied and tend to reduce the stack losses to somewhere around 75-150 CFM with the doors closed. However, when closed, they reduce the radiant heat output about 60%.

Most new construction uses a gas direct vent fireplace. These use a coaxial vent systyem, which allows great flexibility in siting while the best of high efficiency with positive indoor air quality impact. Being sealed combustion, you don't have to worry as much about carbon monoxide into the home. You are not removing indoor air. Most units today have AFUE ratings btw 60-84%, which is amazing for a luminous flame appliance with glowing logs and embers inside a trapezoidal combustion chamber with glass across one side.

Gas fireplaces are either standing pilot or electronic ignition. More and more states will join Calif. in banning standing pilots. Of the electronic ignition systems, Direct Spark Ignition was the first followed by Intermittent Pilot Ignition with Hot Surface Igniters used in special applications. If any of you service gas heart appliances or pellet stoves, I would be happy to help you with any issues. In turn, I will be learning from you guys on large appliance service and troubleshooting.
Thx!
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