Warranty, design, and quality of materials should be on the top of your list when choosing your outdoor wood furnace. There are many options out there so be careful. Question your dealer to make sure he gives accurate answers to your questions. Many of the dealers do this part time and are not insured. The best choice is to find a full time dealer that stocks all parts and has many stoves on hand. The full time dealer is more likely to be in business in the future to help with any of your maintenance needs.
BEWARE BEWARE BEWARE!!!!!!!!!!!!
THINGS YOU SHOULD EXAMINE BEFORE PURCHASING AN OUTDOOR WOOD FURNACE
1. FURNACE DOOR INSULATION
The furnace door is the Achilles heal of the furnace. The door must be well insulated. An example of a poorly insulated door would be one that has an inner water-jacket door with a very thin outer door or one that is altogether poorly insulated. This will cause severe heat loss. Simply stated, this means more fire wood for less heat.
2. TYPE OF DOOR GASKETS
The best doors for your furnace are made of cast mild steel and have a recess in the door gasket. This is covered by a fireproof rope that makes an air tight seal. Silicone or rubber gaskets melt or become deformed due to the heat and eventually break down. Leaky doors can cause run-away fires.
3. TYPE OF DOOR CONSTRUCTION
Doors need to be adjustable in all directions. However, if you don't have a fire rope seal in the door the adjusting of the door won't make any difference. Water jacketed doors are more prone to corrosion and have hoses that can leak. Doors that are close to the ground make the stove hard to open and load in the winter. This type of door requires constant snow removal. The best bet would be to go with a single well-insulated door that has a lock and safety catch.
4. LEGS VS SKIRTING
Stoves without legs have no insulation on the bottom of the stove causing great heat loss. If you try to insulate this void on your own it is impossible to stop the insulation from getting wet. Furnaces with legs will save you time and money because they do not require concrete slabs and are insulated.
5. RUST CONTROL
If you do not take time to learn about rust control it is not a question of if you will replace your wood stove but when!!! Prevention of rust doesn’t need to be expensive. If the stove has several thickness of metal or has dead spots, it prevents circulation of water causing corrosion to occur quickly. When shopping look for a high heat furnace that produces less ash; ash causes corrosion. The first step to rust control is a well-designed stove made of 304 stainless steel.
6. LONGEVITY OF STEELS
Stainless steel will last longer than mild steel in your furnace. But not all stainless steel is a “forever” product. There are many grades of stainless steel and some of them are very prone to rust. Auto exhausts are made of a lower grade 409 stainless steel also known as titanium stainless grade. They rust at high temperatures and corrode completely. Most outdoor wood furnace manufactures went to a low cost 409 grade to get a better image resulting in poorer quality. Since 304 stainless steel is expensive most do not use it. 304 STAINLESS TENDS TO STRESS CRACK AS WELL. Cheap steel will result in CORROSION!!!
7. ANTIFREEZE OR NOT
Most dealers that sell stoves made of cheap material recommend the use of antifreeze so your stove will not freeze up in a power outage. This story is to get you to use anti-freeze because the furnace they are selling has an inferior grade of steel. Anti-freeze is also used to prevent rust in cheaper grades of steel. If the power goes out your stove does not need power to stay lit.
8. INSULATION TYPES
There are three types of insulation; glass, spray foam and bubble wrap. Spray foam has a better R value per inch. However when subjected to the great heat from your furnace it tends to crystallize and break down. Furnaces sweat but foam insulation does not allow it to breathe causing corrosion. The use of bubble wrap only works if used on top of another type of breathable insulation. Avoid this if it is the only type of insulation used. Make sure the insulation you have is breathable.
9. WATER JACKETS
Furnaces with a water jacket on only part of the firebox, such as the horseshoe water jacket, does not allow for the coals on the bottom of the stove to transfer heat as well. Without water on the bottom of the stove much of the heat required when the fire gets low on wood is lost. Then there is not enough heat to rise and support the amount of heat your house may require. The lack of water on the bottom of the stove also means there will be dead pockets which lead to RUST! Some manufactures put grates in the bottom of the stove. Unless the grates are filled with water that will circulate through them, it’s useless. Grates without water will burn through and will be costly to replace. Look for a furnace that has water on the top, bottom and sides for less corrosion and better heat transfer.
10. SIZE OF WATER STORAGE
The size of the water storage is a major consideration in furnaces without forced air draft. If your outdoor wood furnace does not have a 150 gallon capacity, heat loss will occur. Storage systems with a 40-130 gallon capacity require much more wood because your house will drain this system too quickly. If you put a 50 gallon and a 150 gallon drum outside which one do you think will cool down first? Less water can mean twice the wood consumption because it cools down faster. More fluid takes longer to heat, but will last longer. This means less wood burned.
11. NATURAL DRAFT VS FORCED AIR
A natural draft system works when you only plan to burn a very dry wood. Forced air systems, coming through the bottom of the stove, burns green or dry wood. Air injected from the front or top of the stove tends to only get heat from the place were the air is injected. This will build up ashes and a mixture of green and dry wood is required. Be careful of the dealer selling stoves with multiple fans, this only means his stove will not burn wood properly and it will consume more electricity.
12. PRESSURIZED VS OPEN AIR SYSTEMS
To hook into an existing high pressure system the new furnace must be tested to standards and must be rust proof; most outdoor furnaces are not. If you want to tie into an existing pressure system use a large stainless steel water-to-water exchanger. This also allows you to put antifreeze in your home system protecting your expensive in-floor tubes and not use anti-freeze in your outdoor furnace. The cost of putting anti-freeze in your outside system could cost up to $1500 or more and could burn 30% more wood.
13. ASH REMOVAL
Auger systems in an outdoor furnaces just do not work. They sound like a good idea but jam with nails and clog up especially when the ashes get damp and freeze up. Other manufactures want to have you shovel out the ashes every few days. This is ok if you do not mind the loss of your hot coals and do not mind the labor of the job. A system with an ash pan works the best, just pull out the pan and dump your ashes in a fireproof container.
14.WARRANTY WARRANTY WARRANTY
Most outdoor furnaces work well when new, but a good warranty is the most important item you will need in the future. Be VERY CAREFUL with 25 to 30 year warranties that only cover workmanship defects, because only the welding is covered and usually welding is not a big problem. BE AWARE of the maintenance that is required to keep you warranty in force; this can be time consuming and expensive. Do not believe what the dealer tells you. Ask to see the warranty and the owners manual, only what is in writing counts!!! Most warranties have a lot of wiggle room, allowing the manufacturer to get out of paying claims. Most warranties will only pay for parts and not labor. Again be careful because getting a certified welder to your house will be very expensive!!!! Don't get caught not knowing what is and is not covered. Look for a warranty that pays for water analysis and covers rust and corrosion for at least 20 years.
15. HOUSING OR SHELTER OF THE STOVE
Do not buy an outdoor wood furnace that does not come with a fully insulated housing. A furnace without an insulated housing is like a house without insulation. Do not fall for the sales pitch, “You can heat the building that the furnace sits in,” this does not work. Your wood consumption could double due to the heat loss generated from an un-insulated unit. Also there is an increased danger of someone touching the hot stove and getting burned. Thus, buy a fully insulated furnace to drastically reduce heat loss and accidental burns.