Chimney Lining Requirements
for Historic Homes
We're often asked if a chimney liner is required in an old home that was originally built without one. The real answer is that it depends on how you'll use the chimney.
If you're using the chimney for its original intended purpose of burning wood or coal, then generally the building code requirements in effect at the time the house was built will apply under standard practices of grandfathering codes. For example, if the codes in effect in your area in 1905 did not require a chimney liner then code bodies will not normally force you to install a chimney liner now AS LONG AS YOU'RE NOT CHANGING ITS ORIGINAL INTENDED USE - in other words if you will continue to burn wood or coal in this chimney.
An exception would be if your locality enforces a "Maintenance Code" which requires any deficiency to be brought up to today's code standards. If this is so you'll probably face nearly unmanageable upgrades to your home, so these codes are not often applied in old homes as they'd require upgrades to structural, electrical, plumbing, etc.
If you want to burn wood or coal in the fireplace then codes probably would not require a liner. HOWEVER, just because you may have the right to use it "as is" doesn't mean it's smart to do so. We would never endorse blanket use of an unlined chimney. We like to offer this explanation so you understand you're electing to upgrade the chimney for your own safety and/or because the new appliance you're installing requires you to, rather than because someone tells you that codes universally require you to do so as that is not the case. Repair and upgrade your chimney by choice, and because you're concerned with your family's safety, and not because you feel you've been strong-armed into it.
The primary exception to the requirement to line an unlined chimney is when you change its use, at which time you MUST upgrade the chimney to the requirements of the appliance you're using. If you installed a woodstove then the woodstove manufacturer will require the chimney be lined. As a retrofit liner into an unlined chimney, stainless steel is the most widely used method although other materials such as cast-in-place lining systems are available and approved for this use. Likewise, any gas appliance you install will have chimney liner requirements but the type of liner required will vary according to the gas appliance you're installing with a less expensive system often being allowed.
Our Victor gas coal burners and all gas logs that are used in an open fireplace require the chimney be lined AND suitable for use to burn wood. Again, this means stainless steel or equivalent, and that the fireplace should have a smoke test done to verify that it is engineered to draft properly. We recommend a liner no smaller than 6" be used with our Victor gas coal burners. Gas logs will generally require at least 8".
IT IS VERY IMPORTANT to take into consideration the size of the fireplace opening when planning a chimney lining project. The area of the fireplace opening (width x height) determines that the flue should be at least 1/10 the area of the fireplace opening with a square or rectangular flue; a round liner, such as stainless steel, should be at least 1/12 the area of the opening as a round liner encourages optimum draft due to less flow resistance.
To figure the area of a circle, you must remember "Pi-R-Squared" from high school. Multiply the radius (half of the diameter) by itself, and multiply the result by 3.14 - here's how it's done:
6" diameter = 3" Radius
3 x 3 = 9
9 x 3.14 = 28.26"
Thus, a 6" pipe has an area of 28.26 square inches.
So you may not be able to install a 6" liner simply because the appliance is approved for that - you have to install a liner that is big enough to draft the fireplace when burning wood using the 1:10 or 1:12 ratio. That's why we say "lined AND suitable for use with burning wood". If the liner size restricts draft to the point where wood smoke would enter the room, burning an open gas appliance in it would be dangerous as open flame gas logs or gas coals produce carbon monoxide that you cannot see or smell as you can with wood smoke.
Gas coal baskets and gas logs are purely decorative appliances. With the fireplace permanently open and the damper - if there is a damper - clamped open for safety reasons then you'll find that virtually all the heat produced by this open burning appliance is drawn back up the chimney.
In short, the permanent opening of the appliance determines the chimney sizing requirements. A similar quotient is used by all hearth appliance manufacturers to determine chimney sizing requirements whether the appliance is a wood stove, a gas stove, etc. The size of the door opening determines the size of the chimney liner.
Another option available that many homeowners choose due to lower costs and improve heating efficiency is a gas fireplace insert. This is a stove that inserts into the fireplace, and most models now use a dual 3" diameter lining system. And these liners can be aluminum, which is a much less costly alternative to stainless steel.
These do use a glass window so the efficiency is much greater at 80% because the chimney does not remove the heat the appliance has put into your room. Eighty percent efficiency is in the range of a gas furnace so they use fuel wisely while also providing a gorgeous and period look for your fireplace. A thermostat modulates the fire to adjust heat output based on the temperature of the room. You're never overheated and you use less fuel. These direct vent models use a dual 3" aluminum chimney liner system; one liner brings combustion air from outdoors while the other exhausts the gas fumes.
If your budget doesn't allow a complete renovation of the chimney and fireplace, professional installation costs of the repairs and running the gas lines, consider an electric fireplace conversion. With electric fireplace inserts, no venting required, no technical knowledge is needed for installation; it's a completely portable and inexpensive answer. These are not as frivolous and fake as you'd think so you owe it to yourself to take a look at them before rejecting the idea altogether.
In conclusion, the requirements of the chimney lining system are determined by the appliance that vents into it. The appliance you install should be determined by a combination of the look you desire and the heat output, if any, that you expect from it. If you're looking solely for an aesthetic appeal without great heat expectations then a gas coal basket is a great choice with a variety of baskets and frets available to suit any look. If you need heat from the fireplace then choose a gas fireplace insert for its greater efficiency while also enjoying lower costs for the whole project. A gas insert including the chimney liner will probably cost half as much to purchase and install versus an complete chimney and fireplace renovation, while also saving about 30% on gas consumption every time you use it.