Outdoor wood furnaces provide enough heat but not all of them acquire the same capacity as a home heater. There are different models and types to consider when taking home a good quality outdoor furnace. Check the performance, safety, longevity and more importantly, its quality.



First, examine the chimney closely. The pipe length is important if the outdoor furnace has a manual or electric damper. A long chimney is used to draw air over the fire and to keep it burning. An extra chimney length is good if it has a forced-air draft.

Furnaces with chimneys located outside can cool off as compared to those going out to the top. Unburned gases form creosotes as it condenses.

Chimney caps keep the rain out and avoid rusting of firebox. Most manufacturers do not include caps. A clover leaf designed cap is good since it can prevent downdraft.

Also check the insulation. Furnaces should be insulated with a 4 inch thick door. Others have inner water jacketed doors and 2 inch outer doors. A thick door of about 6 inches is much better because the thin layers allow heat loss. Be aware of hollow doors, it provides little insulation.

Doors should have anti-blowjack safety catches to prevent flash burns and the release of gases. Doors with cast or mild steel with a recessed lip on the outer edge is the best. The silicone seal has a type of memory and when the door is closed, it seals tightly in place. Doors with no silicone seal can break down. It will create leaky doors and cause runaway fires.

Doors also need to be adjusted for in, out, up and down, to provide balance. Water jacketed doors are prone to corrosion and some hose leaks.

Door sizes should be large enough and should run from 20 up to 30 inches. A 30 inch size from the door bottom is convenient for easy filling.

Furnaces corrode easily if it has many welded seams and dead spots, preventing water from flowing. Ashes are the main causes of corrosion. A high heat model can prevent this problem. Also, heavy built-in plates take longer to corrode. Some manufacturers use heavy plates at the bottom portion as well as light at the sides to reduce cost.

Outdoor furnaces made from stainless steel can last longer compared to mild steel. Some manufacturers even use low grade stainless steel because it is expensive. The materials you use are important for longer usage.

Antifreeze is a rust inhibitor. It is designed to maintain cooler engines. Downfrost is the best glycol additive for antifreeze. It has great anti-corrosion properties as well as high temperatures and longer life features.

Glass and spray foams are the two basic insulation types. Spray foams tend to crystallize when subjected to greater heat. Foam and sweat insulation cannot allow breathing and can lead to corrosion. Fiberglass bathing with aluminum foil insulation is very liable.

Also test the heating capacity. Variables to consider when testing the furnace heating capacity include geographic location, perimeter size and floor heat or forced air as well as insulation values and heat demands.

Take note that the more seasoned the wood, the more efficient it will burn. When you purchase furnaces, it varies on your choice or type of wood you can burn. Forced air draft furnaces can burn any kind of quality wood.

Hooking onto an existing pressure system can run in high pressure standards. Some outdoor furnaces can even contaminate water units. A large stainless steel water exchanger can help tie your furnace onto a pressure system.

For piping, kitec or polybutylene piping is the best choice. Kitec is easy to install but it does not allow oxygen onto the system. Underground pipes needs to be well insulated. It is placed under a maximum of 18 inches deep to avoid ground water.

Basic safety features to consider are high-limit switches, lockable doors, low pressure systems, insulated handles, safety latches and low water indicators.

Replace components regularly as part of maintenance. Water jackets are cheaper and faster to repair rather than exchanging it. Modular or small parts do not have to be replaced. It can create more seams and lead to corrosion.

A unit should include the best design control such as high limit temperature, water level indicators, outside lights, temperature gauges, aquastats, separate panel boxes, and modifiable fan air velocity.

The CSA or UL standard testing is important. Ask for the testing certification before buying a unit.