Most people assume that if the heat is coming off of a wood stove and the smoke is going up the chimney, everything is fine. It may be, but very often it isn’t. There are two common problems, and a thousand little ones. Let’s only deal with the common problems. The biggest problem of them all is the clearances to combustibles. There are codes, standards and listings that specify how close a hot surface (either the stove or the pipe) can be to a combustible surface. And on top of the codes, standards and listings, there are the manufacturer’s instructions. Let me sort this out together.
Standards, Codes, Listings and Manufacturer’s Instructions
A standard is developed in a test lab. It’s not a rule in itself, but the standards do matter. When a chimney sweep quotes from NFPA211 (the standard covering this area) you should pay attention. But the standard itself is not law.
A code is law. And the codes are made from – you guessed it! – standards. The code doesn’t necessarily match exactly what’s in NFPA211 every time, but it’s highly likely to be very almost exactly the same. This is especially true today as most jurisdictions now use the International Residential Code, which standardized several different codes fairly recently (past few years.)
And then there’s the listing. At UL or a similar lab, they determine that Product XYZ performs in a way that keeps it in the safe guidelines of the standards. And manufacturer’s installation instructions are always included in their listings. So in the end you have to install a woodstove or stovepipe according to the manufacturer’s instructions.
So Get to the Point! (OK! OK!)
You must follow the manufacturer’s instructions of course, but there are generalities we can specify because we know how products have been listed. The graphic here tells you what clearances you need to maintain for an unlisted stove and for single wall stovepipe. There acceptable ways to reduce those clearances as well. I refer you to the NFPA 211 or invite you to call us here at High’s if you need specific information about this. There are products listed for closer clearances than these however. Double Wall Stovepipe is listed for a 6” clearance to combustibles for example. And see what the installation instructions on your stove say. Some stoves are listed for as close as 12” to the wall.
Most people don’t realize Double Wall Stovepipe is even an option. It’s also called DVL and improves the performance of any woodstove. It definitely costs more than ordinary black stovepipe, but it doesn’t break the bank either. DVL is a very nice product and most people would be happier having it if they only knew it was an option. So the way you know if your clearances are OK or not is to read the instructions and break out a measuring tape. It’s that easy.
Proper Sizing of Connectors
Surprisingly, you’ll see the wrong sized connector (stovepipe) on stoves, either too big or too small. The manufacturer’s instructions will always say to use the same size pipe as the stove collar (the flue gas outlet on the top or back of the stove- where the smoke comes out) so this is easy to figure out. If you increase to a larger pipe for some reason, you will give up stove performance, that is the stove won’t draft as well. If you decrease your stovepipe, for several reasons I won’t cover here, you are likely to have draft problems as well. In any event, the stove was engineered to have a certain connector size, and changing the connector size for some reason changes how the stove performs and can even make it unsafe when otherwise installed according to proper clearance! Don’t change the connector size!
- Single walled stovepipe should be secured by three screws at every joint. This is an easy one to check and easy to fix if it needs it.
- Any woodstove, but especially (and absolutely!) fireplace insert woodstoves should have a properly sized stainless steel liner when installed in a masonry chimney. In fact, that’s in most manufacturers’ installation instructions these days, and the codes are increasingly calling for liners on older wood stoves as well. The way to find out if you have one (if you are unsure) is to look down the chimney. The liner should extend out of the top of the tile.
- Read the instructions for information about the area in front of the stove. In general you want 16” of protection in front of the stove door, but again, you go by what the manufacturer says.