You should avoid elbows whenever possible since a straight vertical chimney is the most efficient and will provide the strongest draft.
However, we realize that it is not always possible to run straight out of the stove and out the roof.
When an elbow offset is necessary to avoid obstructions such as rafters, ridgepoles, joists, overhangs, or to line up your stove pipe with wall studs you need to be able to take a proper measurement.
This guide will show you how to measure an offset so you know how much stove or chimney pipe you need for your installation.
An elbow offset consists of two elbows, known as the offset elbow (the elbow on the bottom) and the return elbow (the elbow on the top). Between the two elbows is the connecting pipe.
The distance between the center of the flue on the offset elbow and the center of the flue on the return elbow is known as the "offset".
The distance between the bottom of the offset elbow to the top of the return elbow is known as the "rise".
When measuring, you only need to measure the distance of the offset, then refer to our elbow offset chart to learn the rise based on which elbow kit you choose.
For example, let's say you need to offset the chimney in the attic because a rafter is blocking you from going straight out the roof.
You would measure over from the center of the flue on the chimney where it penetrates the ceiling to the space between two rafters that you intend to run the chimney pipe through. When taking this measurement be sure to keep your tape measure level.
Next, use your "offset" measurement to determine how much chimney pipe you need to complete the connection between lengths AND how much "rise" the connection is going to produce.
Let's say the offset measures 12". When you look at the chart you see that there is no exact 12" offset. That's okay, find the closest measurement, in this case there is an 11" offset if you use a 15° elbow kit or a 12.25" offset if you use a 30° elbow kit.
If you use a 15° elbow kit you will need a 36" length of pipe between the elbows which will result in a 50.25" rise. Maybe you don't have enough room to accommodate the 50.25" rise. In that case let's look at the 30° elbow kit.
The 30° elbow kit has an option for a 12.25" offset requiring an 18" length of chimney pipe to connect the elbows resulting in a 30.25" rise.
You might need to try different combinations to get the right fit. You can Print This Chart and take it with you to do your measuring if needed.
We manufacture elbows in 15° and 30° angles measured from vertical. A 30° elbow is the largest elbow that can be used in an offset with our Class-A chimney pipe.
A 30° and 15° elbow can not be combined to make a 45° for use in our chimney system. Use no more than two pairs of 30° offsets in any one chimney system.
The maximum length of chimney pipe between elbows is not to exceed 72" and a maximum of two chimney sections can be used.
Our kits include an elbow strap to help support the weight of the offset. One elbow strap is needed for each length of pipe used in the offset (2 maximum).