How to Guide: How to Choose Venting for a Direct Vent Gas Fireplace

How to Guide: How to Choose Venting for a Direct Vent Gas Fireplace

Ok, you need an “exhaust” system for your new direct vent gas fireplace.  Not all fireplaces require venting and some don’t require “direct vent” pipe but, the best fireplaces do.  You can find some of these fireplaces here  If you're looking for a "vent free" option, you can find some great options here  Yes, the best fireplaces on the market, generally, use a “direct vent” venting system.  So, you’re probably asking, what does direct vent mean anyway?  Here’s the simplified explanation: The vent pipe is co-axial (there’s an inner and an outer pipe, concentric). The flue gases exit or exhaust through the inner pipe to the outside and the combustion air is drawn in through the outer pipe. The air in the outer pipe doesn’t mix with the flue gases in the inner pipe. This way, by taking fresh air from outside, air is not drawn into the fireplace from the room itself creating the  potential for negative pressure.

Now that we have that figured out, we have to figure out what kind of direct vent system you need.  First, you want to look closely at the installation manual for your fireplace to figure out what types of venting components are allowed for use with your particular unit.  This manual will also have rules on vent lengths, heights, diameters, etc.  Pretty much everything you’ll need to know to install your gas fireplace properly.  The installation manual will provide you with approved manufacturers and vent diameters for various installation types (through the roof, out an exterior wall, etc.) as well as specific venting components with part numbers for various applications.  Remember, it’s a good idea to look over the manual closely as an overview, you want to make sure you will be able to install this fireplace properly for it to function safely and efficiently in your proposed location.

The first step in estimating your vent pipe needs is measuring the physical space where the fireplace is to go and the route in which you would like to vent the fireplace, keeping in mind what was discussed in the manual for approved configurations, etc.  Pick a venting diagram in the manual that looks most like the one you will use in your installation.  Then get out the measuring tape!  Try to be as exact as you can be with your measurements.  There are often helpful diagrams and charts in the installation manuals with directions on how to measure lengths of pipe, 45 degree angles, 90 degree angles and so on.  You’ll also want to note the dimensions for the gas fireplace you will be installing and whether you’ll be venting off the top or the rear of the unit.  These are called “top vent” and “rear vent”.

A large consideration in the installation of the venting is going to be clearance to combustibles, which is how close the outside of the vent pipe is allowed to get to wood, drywall and other “classified” combustibles.  Normally this is 1” but can vary with high heat output gas fireplaces and high heat locations such as a 90 degree elbows off the top of the unit where excessive heat can accumulate.  Another thing you’ll want to determine is, where on the exterior of the building will the “termination” be located.  The “termination” is the end or the cap for the exhaust.  Are you venting through a wall to the exterior for a “horizontal termination” or through the roof with a “vertical termination”.  You’ll want to know the thickness of your walls so you can properly prepare for your “wall penetration”, if venting through an exterior wall to a horizontal termination.  The same consideration should be applied when penetrating the roof.  Is there an attic, where you will have to protect the pipe from insulation contact, rodents gathering food next to that nice warm pipe?  Whether you pass through an exterior wall or through the roof, you’ll want to do this carefully.  Safety is paramount, but you also want to protect your home by weatherproofing properly with approved sealants and good craftsmanship.

Once you’ve made it to the exterior of the building, keep in mind that you will have to prepare for clearances to other features such as ground clearance, soffits, air intakes, inside and outside corners of the building, snow loads and so on.  Again, this is where you must refer to the installation manual to determine manufacturer's recommended installation practices.  If you’ve made it this far, you’ve measured and found the best and safest venting route for your gas fireplace or stove.  At this point, you’re ready to source your materials and start picking out the components that will best accommodate your particular situation.  You may want some help at this point from a professional to avoid ordering the wrong parts, or having to over order to play it safe.  Remember, measure carefully and feel free to give us a call if you need some help. 

Thanks for taking the time to read our blog and good luck!



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