Pellet Stove Venting: Should You Use Three inch or Four inch ?

If installing your pellet stove venting at 2,500 feet or more above sea level, you definitely need four inch pipe. This is because at this altitude the oxygen level in the air is lower and the stove needs to push more air through to burn effectively.

At lower altitudes, you may still need four inch venting depending on the length of run of your pipe and the number of bends in it.

Converting from three to four inch stove vent pipe is very easy - an adapter fits directly on to the output vent of the stove.

With some stoves, you don't have a choice. They are designed for a four inch stove vent and this should never be reduced, unless the manufacturer allows this option, or you will throttle the stove.

The maximum allowed horizontal run of the vent pipe is usually four feet.
The maximum vertical run of three inch pipe is usually fifteen feet. More than that and you need four inch pipe.

Calculating Your Pellet Stove Venting Size

Now you need to calculate the effective length of your pipe run. Changing the direction of the venting when you use elbows or a clean-out tee increases the effective length of the pipe.

Each foot of horizontal or 45 degree pipe has a value of 1 foot
Each foot of vertical pipe has a value of 0.5 feet
A clean-out tee or a 90 degree elbow has a value of 5 feet
An elbow with a 45 degree angle has a value of 3 feet

So what you have to do is look at your prospective pipe run and add up the effective lengths.

For instance:
Two foot horizontal run to the wall = 2 feet
Clean-out tee = 5 feet
Six foot vertical run = 3 feet
90 degree turn = 5 feet
Two feet horizontal through wall = 2 feet

Add them up and the effective pipe length of this configuration is 17 feet and you need four inch pipe.

If you went straight through the wall, and then up:
4 feet horizontal through wall = 4 feet
Clean-out tee outside = 5 feet
6 foot vertical run = 3 feet

Add these up and you get 12 feet - fine for three inch pipe

If in doubt, use four inch venting anyway.

For more venting information, have a look at: