So, you plan to build an offset smoker? Congrats! It’s a large undertaking, but fun and educational. This page is thought to be your guide when building your own offset smoker.
How it works
An offset smoker is typically using wood as a fuel source. ‘Offset’ means the fire is offset, typically sideways, so you get the indirect heat setup that is key to barbecue.
There are roughly two types of offset smokers.
Normal offset smoker
As you can see from the illustration above, the fire is in the firebox to the right. Hot air and smoke travels through the food chamber and out through the smoke stack. This is a ‘simple’ design that works well. Depending on how it is constructed it typically runs hotter in the firebox end of the food chamber but this can be compensated for.
Reverse Flow Offset Smoker
As illustrated the reverse flow smoker uses a long baffle to move air all the way through the food chamber before being turned around, or reversed. This helps even out temperature differences since the radiant heat from the baffle and food chamber walls heat up the air more evenly. The drawback is that air must travel longer, thereby decreasing draft. The most obvious sign of a reverse flow offset smoker is the chimney being mounted on the same side as the firebox.
Reverse Flow Offset Smoker – a different version
The main idea behind reverse flow is (as mentioned) to reduce temperature differences in the food chamber. Completely depending on different constructions an offset smoker is typically hotter the closer to the fire you get. A common way to solve this is to use a slanting baffle perforated with different size holes. See picture above. This distributes heat more evenly when it enters the food chamber.
If at all unsure of which to build, start with a normal offset smoker.
1. Start with the food chamber
Start with the food chamber and calculate the rest based on food chamber size. Given a certain food chamber size the firebox should be roughly 1/3 or 1/4 the size. For smaller so called backyard smokers 1/3 is a good measure. For bigger smokers 1/4 is better to aim for. If the smoker is 12-15 feet or longer then you can make it even smaller (proportionally). The important thing with the firebox is having unlimited oxygen supply. You also need to fit 5-6 logs in there.
2. Calculate smoke stack size
To get an offset smoker to work well you need a clean burning fire. A clean burning fire requires good draft, which is accomplished with long and large diameter smoke stack.
3. Dimension the firebox
The firebox should at the very least have the size to fit a few logs and make a good fire. For normal to large size smokers it typically needs to be a bit bigger than that. The rule of thumb is that you need to build a fire large enough to heat up and sustain temp in the food chamber. The firebox opening must be the same size as, or greater than, the smoke stack opening. This is to avoid throttling draft.