How does a double barrel wood stove work to produce more heat

A double barrel wood stove produces more heat than a single barrel stove. The first (lower) barrel containing the burning wood. The second (higher) barrel is placed in line with the flue and contain tubes that get heated by the rising smoke. The heated tubes become warm and act as both an extra heat mass to radiate heat, and are often used in conjunction with a fan to blow cooler air through the tubes which is rapidly heated.

Double barrel heaters are a very popular and inexpensive way to keep a workshop toasty warm.

What is a double barrel wood stove?

A double barrel wood stove is exactly what it’s name implies. It is a wood stove that consists of two barrels, usually equally sized. The barrels are usually oriented horizontally, but placed in a vertical arrangement, with one barrel above another barrel.

Each barrel serves a different purpose, one barrel is to burn the wood, the other barrel is to reclaim what would otherwise be lost heat.

typical DIY double barrel wood stove
Typical Double Barrel Wood Stove

What is the advantage of a double barrel wood stove?

Making a wood stove from a single 55 gallon drum, and burning a fire inside that barrel is simple enough, and will usually heat an as area well as most fire places or wood stoves.

Where a double barrel wood stoves excels, and where it has its advantage, is that the second barrel extracts more heat from hot air flow up and out of the flue. The second barrel acts as a heat exchanger. In simple terms the advantage of a double barrel wood stove is that it burns less wood for an equilivent amount of heat output (its fuel efficient).

Double barrel wood stove design

Many double barrel wood stoves are home made, from 55 gallon drums, therefore both drums are usually equally sized.

The barrels are stacked horizontally on top of each other, separated although connected by a short length of stove pipe.

The bottom barrel is raised off the ground, and functions as the fire chamber. This is where the firewood is loaded and the fire is contained.

The upper barrel functions as the heat exchanger. The heat exchanger has tubes running along inside the barrel, these tubes are sealed so no smoke and gas can escape. Cool air is heated as it pushed through the tubes, created the effect of a fan powered heater.

Building a double barrel wood stove with built-in pizza oven, and smoker in upper barrel

Double Barrel Stove Kit – DIY

These are the parts that make the double barrel stove kit as used in the video.

Barrel Stove Kit
Add this for the heat exchanger (top barrel)

Disadvantages of, and how to make a double barrel stove more efficient

Double barrel wood stoves, don’t have engineers working on improving designs, so the design can certainly be improved. Here are some sure fire ways to make a double barrel stove more efficient.

Disadvantage – can be difficult to control the burn rate and heat output.
Solution – install a damper in the piece of stove pipe connecting the upper barrel to the lower barrel.

Disadvantage – wood burning barrel stoves can burn through the barrel material quickly.
Solution – select barrels with a heavy gauge steel, or use a beer keg made from stainless steel.

Disadvantage – barrel stoves don’t have the heat mass to keep radiating heat after a fire starts burning down.
Solution – Line the inside of the stove with firebrick or fireclay. Fireclay could help you turn your double barrel wood stove into a great pizza oven.

Adding firebricks to a wood burning barrel stove

Disadvantage – The upper barrel slows down and cools the smoke too much causing creosote buildup.
Solution – install 2 x flue pipes between the lower and upper barrels, and add an 8″ flue pipe (not 6″) to avoid restricting the flowing from the upper barrel through to the output of the flue.

Upright barrel stove

Don’t get confused, an upright barrel stove is not the same as a double barrel wood stove. A upright barrel stove may be used for heating and cooking (same as a double barrel stove), but the upright barrel stove does not have a heat exchanger installed.

Here’s a link to an upright barrel stove build.