vent free, vented?

Old 12-27-03, 06:19 PM
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vent free, vented?

i live in michigan and have recently finished my basement. i would like to install a corner natural gas fireplace down there. question is can i vent (bvent) this fireplace by tying into my existing natural gas furnace vent. the existing furnace vent is 6" i believe, with the water heater's 3" vent 90ing into it. or should i go ventless? (lot's of negative on ventless i.e. moisture and oxygen depletion) would it be possible to direct vent approximately 8 feet to an outside wall? what are my options? the fireplace would be used for looks as well as a heat source since it is in a basement and in michigan. any info or links would sure help.
Old 12-27-03, 06:59 PM
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Hello rtcatzrt600. Welcome to the Do-It-Yourself Web Site and this fireplace topic.

The last thing you would want to do is tie any other appliance into an existing vent. The reason is vent overloading.

The current vent is or should be sized for the existing appliances. Added any additional load to the existing vent will be more than it can safely handle.

When that happens, spillage will occur. Spillage referrs to the excess fumes the vent system cannot handle. These excess fumes will spill back into the room or area.

Spillage can aslo create operational problems not visable to the eye in flame charactorists. Such will or can produce carbon monoixdes and other unhealthy byproducts of combustion.

Best bet would be to install the appliance with it's own venting system, following mfg's recommendations and all local codes.

Unvented heaters are often not legal in some areas, restricted as to locations to be used in or do not meet codes, etc.

In any case, all heaters require oxygen for combustion. The area proposed to install this unit must have an outside source of fresh oxygen in the form of a vent to allow fresh air to enter.

Plenty of items to take into consideration prior to purchase and installation. May be best to contact the local codes office for more specific information and advice from a professional installer in your immediate area.

If you need further assistance, use the REPLY button to add any additional information or ask additional questions. Doing so will automatically move your question to the top of the forums list of questions.

Regards & Good Luck. Sharp Advice.
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Old 12-27-03, 07:02 PM
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You bring up some good points and the best is to read the below article I wrote a while back. The issue of the distance would be listed in the brand that you are interested in. Some units can be vented out to the exterior wall by as much as 20 feet horizontially.

Ventless Units - These are not allowed in Michigan - I know, then why do they sell them? Nothing restricts the sale but installations have been done by the DIY'er but even a vented unit should be installed by a licensed installer.


Less involved installation
Potential to be installed in many places, BUT must follow room sizing requirements (typical unvented fireplace requires 96' x 20' room)
Very efficient in burning of gas, but uses heated room air for combustion


Air quality issues/health concerns
Typical sizing guidelines for an average fireplace size (30,000 BTU's) require a 96' x 20' room size - or 1,920 sq. ft. to safely accommodate unvented products
Illegal in many states and municipalities
A typical (unvented) natural gas stove or fireplace releases a gallon of water vapor every 2 to 3 hours of operation - potentially causing mildew issues*
May require more service to ensure dust, pet hair, and other chemicals are not interfering with the unit
For safety reasons cannot be run for extended periods of time - Maximum Use- 4 to 5 Hours per day.
Requires permanent fixed opening to the outside for proper room ventilation


The codes concerning ventless fireplaces was done as there has been loss of life.

The ODS - Oxygen Depletion Sensor that was invented was to prevent loss of life but these only work when there is less that 18% oxygen within the room. Normal oxygen levels are around 21- 24% within a home. Granted, they have been around for about 40 years or so but if it was so good, why are there laws prohibiting them? One reason is the required maintainance of the sensor itself. This should be checked every 2 years but not many do. As time goes by, I'm sure improvements will be made but since everyone does not have this safety device, the laws were written to protect everyone from the possibility of accidents. For some, this OSD setting may be too low due to health issues and life threatening accidents do occur. Then we have the do-it-yourselfer who doesn't follow manufacturers instructions. This is what has caused the laws to govern their installation or shall I say prohibiting their installation.

“Direct Vent” appliances are ones that draw outside air for combustion and exhaust the flue products within the same closed, double pipe system. Tying this into your furnace is not an option. You may confirm this with your local Building Inspector.

Hope this helps!

Last edited by Doug Aleshire; 12-27-03 at 07:25 PM.

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