portage and Main Outdoor Water Furnaces
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Portage & Main Outdoor Water Furnaces FAQ

Please note that the questions have come from our customers. They have been asked when inquiring about the Portage & Main Outdoor Water Furnace; however the industry has acquired terms such as boilers, stoves, furnaces, outside wood stoves, hydronic-heaters, etc therefore if the question was asked using such terms we used it as asked.

FAQ Categories for Wood Burning Furnaces:

  1. Portage & Main Outdoor Water Furnace General Questions
  2. Why Portage & Main Outdoor Water Furnaces are Best
  3. Portage & Main Outdoor Water Furnace Installation
  4. Portage & Main Outdoor Water Furnace Operations
  5. Portage & Main Outdoor Water Furnace Maintenance
  6. Portage & Main Outdoor Water Furnace Warranty
  7. Portage & Main Outdoor Water Furnace Customer Information & Requests
  8. Portage & Main Outdoor Water Furnace Wood Burning Impact on the Environment
  9. Average Heat Values in Various Species of Wood


1. General Questions for Wood Burning Furnaces

What is the Portage & Main Outdoor Water Furnace?

Portage & Main Outdoor Water Furnaces are designed to look like an attractive storage building and installed outside the building to be heated. The water jacket surrounds the furnace firebox and the heat is transferred from the wood fire to the water. It is a safe and efficient way to heat your building with wood. They are called water furnaces because they circulate hot water to provide heating needs. They have been referred to as outside wood furnaces because they are outside and burn wood.

Can an outdoor wood furnace provide all the heat and hot water I need?

Certainly! Your Portage & Main Outdoor Water Furnace Dealer will assess your heating requirements and recommend the size of outdoor wood furnace that meets your needs. Best burn practices are recommended. Correct sizing of unit will reduce smoldering. Best to tend fire twice daily.

How is the heat from the outside wood furnace transferred to the building?

An outdoor water furnace is like a boiler however the Portage & Main Outdoor Water Furnace is non-pressurized. They are atmospheric vented—they are very safe.

Your building/home does not need to have hot water heat—the Portage & Main Outdoor Water Furnace system will easily interface with most heating systems—water to air or direct circulation heating system. The heat from the p&M outdoor water furnace fire is transferred to water that is stored in the system. This hot water is circulated from the p&M outside water furnace to the home and back to the furnace through an underground insulated pipe.

I have a forced air heating system with ductwork and registers. Will a Portage & Main Outdoor wood furnace work in my home?

Yes. The Portage & Main Outdoor Water Furnaces are designed to interface very easily with any forced air heating system.

The most simple of all installations is a water-to-air heat exchanger (radiator) very easily placed in your furnace plenum. Your furnace operates in "fan-only" mode to blow very warm air throughout your home without burning any gas.

Can I heat more than one building?

Yes. The Portage & Main Outdoor Water Furnace units are designed with two feed lines making it easy to heat two or more buildings.

What else can be heated by an outdoor wood furnace?

The Portage & Main Outdoor Water Furnace can efficiently heat your home, domestic water, hot tubs, pools, garages, barns, workshops, any commercial building, and other commercial uses including green houses, dairies, veal barns, poultry barns, fish farms etc. Please discuss your specific requirements with a P&M dealer.

How large of a furnace do I need?

Consider the square footage of the building(s), ceiling heights, quality of insulation, number of buildings or other demands on the system. Your authorized Portage & Main Outdoor Water Furnace dealer or consultant will be able to assist you in determining your heating requirements.

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2. Why Portage & Main Outdoor Water Furnaces are Best

Portage & Main Outdoor Water Furnaces addresses the two most common concerns people have when purchasing an outdoor boiler—wood consumption and life expectancy. Most outdoor boilers/water furnaces are straight shot design resulting in sparks and fire exiting the chimney resulting in excessive heat loss up the chimney. The Portage & Main Outdoor Furnaces are designed with a multi-pass for the flue gas resulting in the most efficient heat transfer.

Double welding (boiler style), ¼" cold rolled W44 steel and a great design make for long life.

It stands to reason, that when the Portage & Main Outdoor Wood Furnaces use 1/3 to ½ the wood, expected savings on wood purchase would be 30-50% or more. Considering that wood costs can range around CDN $75.00 - $150.00/per cord, the savings can really add up. Since P & M furnaces can burn larger pieces of wood it will dramatically reduce time spent preparing the wood for increased savings on time and resources.

There is no need to be concerned about sparks up the stack. Sparks are dangerous. Our Portage & Main Outdoor Water Furnace users do not need to be concerned about dry grasses or hay stacks, etc. catching fire from stack sparks. Sparks let off from other brands are dangerous and mean the furnace is less efficient.

How much money can I save by heating my home and hot water with an outdoor wood furnace?

Savings are substantial, even if you already heat with wood consider that the Portage & Main Outdoor Water Furnace use ½ to 1/3 less wood to produce the equivalent btu’s of most other outdoor wood furnaces.

For other savings calculations, please refer to the chart the fuel comparison chart.

What is the Portage & Main Outdoor Water Furnace? Is it a boiler?

The Portage & Main Outdoor Water Furnaces are designed to look like an attractive storage building and are installed outside of the, home or building to be heated. The water jacket surrounds the furnace firebox and the heat is transferred from the wood fire to the water. It is a safe and efficient way to heat your home with wood. The Portage & Main Outdoor Water Furnace is also available in an un-insulated model which can be installed in a building you provide. Portage & Main Outdoor Water Furnaces are non-pressurized. They are atmospheric vented, which means they are very safe. Boiler usually refers to pressurized heating vessels.

Why do Portage & Main Outdoor Water Furnaces have round fireboxes?

The Steam Engines were built round for a reason! The round, barrel-shaped firebox design has passed the test of time. Round is the strongest shape for a firebox. Round has fewer welds which translates into greater strength and longevity. Round has minimal expansion or contraction. Round means less weld stress. Round provides the best heat transfer and the highest efficiency based on normal fire burn practices. Other shapes have been tried by other companies but none have proven to be more effective. No other firebox design has been tested and proven more effective.

What kind of insulation does the furnace have?

Portage & Main Outdoor Water Furnace use high grade R20 6" thick fiberglass insulation. This will not breakdown and lose heat like spray-on foam. We use fiberglass insulation, for the same reason it is used in home construction—it breathes—snow doesn't melt off our roof.

How thick is the firebox steel?

Portage & Main Outdoor Water Furnace fireboxes are made from 1/4" W44 cold rolled mild steel-which has proven to be the longest lasting, most welder friendly and easily accessible steel for outdoor wood furnaces. Ask your local welder friend, if you are not sure of the advantages of mild steel over stainless steel.

What are the advantages of ¼" cold rolled mild steel over stainless steel?

Cold rolled ¼" W44 steel is very uniform, long lasting and welder friendly. This is why it is recommended for outdoor water furnaces. In contrast, stainless steel is susceptible to stress corrosion cracking due to its high thermal expansion. Most stainless steel websites indicate that stainless steel is designed for cosmetic finish applications—automobile trim, architectural moldings, kitchen equipment, etc. Stainless steel units require oxygen to service i.e. repair welding.

Mild steel is an ideal choice because of its higher strength, and lower susceptibly to cracking, leaks and broken seams due to the stresses and corrosive environment that outdoor wood furnace metals are exposed to while in use.

There are several reasons why Portage & Main Outdoor Water Furnaces are made of 1/4" W44 cold rolled mild steel—the best material for this application. Piney Manufacturing is proud of Portage & Main Outdoor Water Furnaces and confidently stand behind their outdoor water furnaces with the best full warranty in the industry.

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3. Portage & Main Furnace Installation

How complicated is the installation?

Installation is simple. A lot of Portage & Main Outdoor Water Furnace owners install their systems themselves. Portage & Main Outdoor Water Furnace dealers can direct your installation or have installers they can refer to you.

Can I install the furnace myself?

Certainly! You need to be able to sweat pipe and have access to a few necessary tools. Portage & Main Outdoor Water Furnace has a complete installation manual and design options that make installs straightforward.

Will I lose heat if I place the outdoor wood furnace a long way from my home?

We recommend Urecon Dual pex Flex Underground pipe for installation. The specs on this pipe indicate that it loses only about 1 degree in 200 feet. This is a very insignificant loss and will not affect heating abilities. Supply/return line is buried about 2-1/2 feet under ground.

You can place the furnace anywhere you desire within your insurance guidelines or your municipality/county or state/provincial codes. The only additional cost is for the insulated pipe and perhaps larger circulation pumps. When two or more buildings are to be heated, it is cost effective to locate the outdoor furnace between the two buildings.

What electricity must be supplied to the furnace?

Wood burning Portage & Main Outdoor Water Furnace are designed to run on 110v electricity. Many homeowners add an additional breaker to their electrical panel/box for the outdoor furnace.

How deep should the electric line be buried?

The electrical lines are usually buried in the same trench as the underground pipe, which is usually at least 2.5 feet deep however, you are encouraged to consult your local codes.

Is a chimney cap required?

Portage & Main Outdoor Water Furnaces have chimney caps because most insurance companies require them. With the multi-pass heat exchanger which has the flue gases travel 5 feet horizontally, make a 180 degree turn and travel another five feet horizontally before exiting the chimney, there is no likely-hood that you will ever see flames or even sparks exiting the chimney of a Portage & Main Outdoor Water Furnace. They however keep rain out of the furnace in the summer.

Is a cement pad required?

We recommend a cement pad.

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4. Portage & Main Furnace Operations

How complicated is it to operate and maintain the Portage & Main Outdoor Water Furnace?

The Portage & Main Outdoor Water Furnace has automatic digital controls (programmable to within one degree)—when heat is needed, a fan automatically turns on and provides fresh air to the furnace which enhances the fire and heat transfer. When heat is no longer needed, the fan automatically turns off and the fire slows down until heat is required again. Portage & Main Outdoor Water Furnaces introduce air over and under the fire for a very efficient burn.

Operation of the Portage & Main Outdoor Water Furnace is very easy. The horizontal heat exchanger requires a simple sweep forward then back to clean it—as it is part of the reason for the Portage & Main Outdoor Wood Furnace burning ½ to 1/3 less wood that other furnaces, our customers agree that for the few seconds it takes to clean the exchanger with the special included clean out tool they would rather do the clean out that spend many extra hours with a chain saw in the woods cutting twice as much wood.

Our furnaces also have a light-weigh, durable, easy to remove and dump ash pan. Again as Portage & Main owners realize that ashes cause corrosion they are more than happy to remove the ashes as required. Of course wood needs to be added once or twice in 24 hours. How often and how much wood to add depends on type of wood, area heating, insulation of building, outside temperatures, etc.

How often do I need to add wood?

It can not be emphasized enough! The Portage & Main Outdoor Water Furnace uses ½ to 1/3 less wood than other outdoor wood furnaces. This means that your need to add less wood. The amount depends upon how much space you are trying to heat, how good your insulation is, the type of wood you are burning, and a few other factors. Under normal conditions, a properly sized furnace will require one or two fills per day. In the coldest weather, you may need to add wood a second time when one fill per day may not last a full 24 hours.

Why is the blower fan system better?

The Portage & Main Outdoor Water Furnace has air injected under the grates and over the fire to allow for a more complete burn of gases—quick recovery and reduced smoke emissions.

A forced draft system blows only a measured amount of air to the fire. This allows for quick heat recovery when necessary while at the same time maintaining a controlled burn.

What is the cost of electricity to run the pump and blower fan?

This will depend upon local electric rates, but recent customers have reported that their electric bill increased roughly CDN $2.50 per month—the annual cost to run the pump and fan is very small.

How is the ash removed?

The easily removed, non-corrugated, galvanized ash pan makes ash removal simple. It takes only seconds to remove ash pan and dump ashes into a metal container. Portage & Main customers do not mind this simple procedure as they realize that ash is an insulator, prevents heat transfer and a cause of corrosion.

How often will I to remove ash?

Taking only 5 - 10 seconds, how often depends on type, quality and amount of wood used. Usually once or twice a week is sufficient.

Is there any danger of causing a fire with an outdoor wood furnace?

With the heating system out of the home, risk of fire is greatly reduced. Normally you will locate the outdoor wood furnace at least 50 feet from your home or other buildings ( or as per local government/insurance recommendations). Of course with the Portage & Main Outdoor Wood Furnace efficient multi-pass heat exchanger with horizontal smoke travel, the risk of a fire starting from chimney sparks is eliminated.

Will my indoor furnace still operate if the outside furnace were shut down for any reason?

You can design you indoor furnace to become a back up and would provide heat if needed.

Do I have to worry about my outdoor wood furnace system freezing?

With 180 degree water, the system will never freeze as long as the outdoor furnace is running and the pump is circulating. The use of antifreeze provides peace of mind. Portage & Main Outdoor Wood Furnaces are well insulated and waterproof unit with a 2" insulated base. No legs for the wind to blow through—no heat loss from underneath the furnace. The ash pan frame allows for a convenient fill height.

What should I do with the outdoor furnace if I go on vacation in the Winter?

There are various factors to consider such as length of time away, heating requirements while away, anticipated weather to be while you are away? If you only plan to be a way for a week-end you could turn down your indoor thermostat, fill the furnace full of wood and turn off the draft fan, and enjoy your weekend away.

Away for a longer period, you should still turn down the indoor thermostat, but make arrangements to have a friend or neighbor feed your furnace.

Some outdoor wood furnace owners, who plan to be away for extended periods, install an electric back up boiler or furnace. Discuss you options with your dealer.

Should I use antifreeze?

The advantages to using antifreeze include freeze protection, corrosion resistance and may increase the life of your pump. The use of propylene glycol gives peace of mind Portage & Main Outdoor Water Furnaces distributor recommend the environmentally-friendly propylene glycol to customers who use antifreeze.

What happens if we have a power outage?

Most home heating systems require a power source. If power outages are common in your area, we recommend that you install a generator. A small generator will ensure heat for extended power outage.

Is a Portage & Main Outdoor Water Furnace pressurized?

Portage & Main Outdoor Water Furnaces are non-pressurized. They are atmospheric vented. They are very safe. When it is connected to a home that has a pressurized boiler, the heat from the outside water furnace is transferred to the inside pressurized water by using a plate heat exchanger.

How does the Portage & Main Outdoor Water Furnace heat my domestic hot water?

The water from the outside wood furnace is never mixed with potable hot water, the heat is transferred from the outdoor furnace to indoor potable water through a plate heat exchanger or the more common side arm exchanger. These exchangers enable homeowners to enjoy an endless supply of domestic hot water.

My boiler is a pressurized system, how does an outdoor wood furnace connect to these systems?

A plate heat exchanger transfers heat from the outdoor wood furnace to your home, keeping your pressurized system safe, and providing operational efficiency which allows you achieve considerable savings.

Do you have to add water? How?

Portage & Main Outdoor Water Furnaces are non-pressurized and open to the atmosphere, water can evaporate from the system. The very convenient float indicates when fluid should be added. The Portage & Main has no sight glass or tube to discolor. The breather tube, filler pipe have unique design with reduces evaporation. Normally, the addition of water is required only once or twice a year.

Do you have to drain/flush the water out of the furnace?

No. It is not necessary to drain or flush the water out of the furnace. In fact is recommended that you do not flush your system as the flushing adds oxygen to the system. Oxygen promotes corrosion.

What is the proper pH level for the water?

Certified boiler treatment for the original install is supplied with your furnace. Certified boiler treatment is manufactures in Minnesota. It is specially formatted for use with Portage and Main Outdoor Water Furnaces. Certified boiler treatment will satisfy pH requirement provided that soft water (non treated, lake or rain water) has been used. Your authorized Portage & Main Outdoor Water Furnace will have testing strips to monitor your pH levels.

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5. Portage & Main Water Furnace Maintenance

What are the regular maintenance items?

Portage & Main Outdoor Water Furnace require simple maintenance

  • Remove ash as needed—generally once or twice per week depending upon the wood you burn. See your Operator’s Manual for more details.
  • Clean multi-pass heat exchanger with simple forward and backward sweep
  • Add water to the system when ever the water float level drops to add. The addition of water is normally only required once or twice a year.
  • Clean the water filter via the filter by-pass (as per your design). On occasion, disassemble the filter and flush it out or replace filter

Do Portage & Main Outdoor Water Furnace require any creosote maintenance?

Yes, but unlike other furnaces, Portage & Main Outdoor Water Furnace creosote maintenance is easy to do because of simple access doors. A simple pull to the front with the clean out tool and push to the back to re-burn completes the creosote maintenance. It is a simple task, takes only a few seconds.

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6. Portage & Main Outdoor Water Furnace Warranty

How long is your warranty?

The manufacturers of Portage & Main Outdoor Water Furnaces, piney Manufacturing  warrants the Wood burning ML 30, ML 36, ML 42 and ML 54 Wood Furnace with the 25 year Silver Jubilee to the original owner. Included in the Silver Jubilee Warranty is a 10 year non prorated warranty against faulty material or workmanship. Electrical components carry their manufactures 1 year warranty.

Warranty prices are based on the original selling price. Portage & Main Outdoor Water Furnace does not warrant against freezing, over heating, any furnace that has been altered, pressurizing, or the use of inappropriate fuels and negligence. transportation, installation or loss of fluids are not covered. It is the responsibility of the owner to follow proper maintenance procedures as outlined in the Operator’s Manual. All furnaces must have authorized water treatment (Certified Boiler Teatment) added to their furnace water and a water sample must be sent in for testing annually. See your Operator’s Manual for complete warranty details.

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7. Portage & Main Outdoor Water Furnace Customer Information & Requests

Who is Portage & Main Outdoor Water Furnaces?

Portage & Main Outdoor Water Furnaces are manufactured by one of the leading manufacturers of outdoor wood furnaces in Northern America. We were founded in 1973 and named after one of the coldest intersections in North America and have since expanded to include four models of wood burning units as well as wood pellet burners, wood chip, bio-fuels and coal stoker units. Based in piney, Manitoba, where the winter temperatures can drop to -40 °C, we know the value of reliable, efficient, long-lasting, heating systems.

Portage & Main Outdoor Water Furnaces also known as Portage & Main Outdoor Wood Furnaces, outdoor stoves, outdoor boilers have been supplying heat for homes and business since 1973. The industry standard indicates they are Outdoor Water Furnaces (as they are non-pressurized) that are also outdoor wood furnaces.

Where can I get more information?

The Portage & Main Outdoor Water Furnace team consists of outdoor furnace experts who are capable of answering questions you may have. please do not hesitate to call us at (800) 561-0700, or fill out the following form:


*Required fields.

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8. Portage & Main Outdoor Water Furnaces Impact on the Environment

What impact does burning wood have on the environment?

Burning wood has a positive effect on the environment:

  • No net carbon dioxide increase—wood is a totally renewable resource, which, when burned, results in no net carbon dioxide increase. Carbon dioxide is a part of the natural plant-growth cycle and occurs naturally when trees are allowed to rot on the forest floor.
  • Reduction in greenhouse emission because fossil fuels, when burned, release carbon dioxide which otherwise would stay trapped in the earth. Fossil fuel emissions cause a net increase in carbon dioxide, which is believed to be responsible for the heat-trapping "greenhouse effect." So when heating with wood rather than fossil fuels, you actually achieve a net reduction in greenhouse gas emissions. If you are burning wood you are not using fossil fuels.
  • In addition, harvesting firewood has a pruning effect on forests, which allows net growth to flourish. As trees grow they absorb carbon dioxide.
  • Most people burn wood from their local area so it helps the local economy.
  • Using wood as an energy source reduces our nation’s dependency on oil. Heating with wood may sound old fashioned, however, it is truly a sustainable form of energy. Many call it independence.
  • Using wood provides security and satisfaction. Research experts indicate that within a few years we will likely have used/consumed over one-half of the available fossil fuels. With the present, rapidly increasing consumption, there is a fear of running out of fossil fuels. Solar, hydrogen fuel cells and other energy technologies have yet to prove that they are as sustainable as wood energy

A wood burning system is the right choice for the increasing number of consumers who are concerned about our environment. Wood energy is green energy—smart energy that is simply the best!

Is wood a "Renewable Resource"?

Wood is most definitely a sustainable resource that has been used since the beginning of time.

Renewable Resource is defined as a source that can be naturally restored or replenished in the same timeframe that is compatible with mankind’s normal use. The heat energy from wood burning is actually the sun’s energy stored in the wood and later released in a wood burning furnace. Proper harvesting of wood is actually a pruning effect on our forests.

What about wood burning adding to the greenhouse gasses?

Carbon dioxide is the primary greenhouse gas that all fuels produce when they are burnt. The average global temperature rises when the atmospheric concentration of greenhouse gasses is increased.

A tree as it grows absorbs carbon dioxide from the air storing it in the wood as carbon. Carbon makes up about half of the wood’s weight. A growing tree uses more carbon dioxide than a mature tree. Burning wood releases the same amount of carbon as that the same wood would release if left to decay on the forest floor. Wood is part of the natural carbon/carbon dioxide cycle. trees need carbon dioxide to grow. Wood energy—it is green energy.

Trees used for wood energy enable part of the forest's annual growth to be used wisely in heating our homes rather than to decay and rot in the natural and forest fire cycle. Firewood is a natural energy product from the forest. Burning wood is energy used not wasted.

The carbon in coal, oil and gas (fossil fuels), by contrast, are taken from underground stores, where they were deposited by nature, and released into the air without means for equal re-absorption.

Wood burning is completely safe in terms of "Greenhouse Gasses"—Burning wood actually helps reduce greenhouse gas emissions by displacing the use of oil, gas and coal

Is there enough wood?

The North American continent fortunately has an abundant supply of wood. proper management and care of our forests will allow for a continual source of heating energy. Gas and oil are being depleted at an astonishing rate.

Wood is appropriate to our resources as it is affordable, renewable sustainable and a secure heating method.

Wood—naturally renews itself and adds no greenhouse gasses to our environment—is meant for human consumption.

Good Forest Conservation policies improve the abundance of wood. As a young tree uses more carbon dioxide than a mature tree, it is wise to harvest mature trees with re-forestation programs in place. Maintaining wood lots is good for the environment. In fact some forest management programs have semi-loads of wood for delivery as it saves them from having to pay dumping fees for the excess wood that requires harvesting. Wood for energy is smart energy and definitely green energy.

Does wood burning save money over burning fossil fuels?

Yes! per Btu, wood is much less expensive than fossil fuels. Please view the alternative heating chart below and determine for yourself with the energy cost from your area. For example in some areas, natural gas is three times the cost of wood, electricity is seven times the cost of wood. These examples have been determined by a customer who purchases his wood; however many people have an unlimited supply of free wood to harvest on their own property.

Alternative Fuel Cost Comparison
For Multi-Building-Farms - 300,000,000 Btu's per Year

Fuel Yield in BTU's> Required Annually Unit cost Annual Cost
Coal 19,00,00 Btu/ton 16 tons 39.00/ton* $416.00
Fuel Oil 36,300 Btu/ton 8,264    
Natural Gas 35,301 Btu/ton 8,500 m³ 42 mm³**  
propane 24,200 Bt/l 12,400 l    
Electricity 3,413 Bt/kWh 387,900 kWh    
Wood 17,000,000 Btu/cord 18 cords    
Wood† 17,000,000 Btu/cord 9-12 cords    

prices listed are for comparison purposes only. please contact your regional supplier for your own calculations. The unit costs provided are example only.

* Freight for coal would have to be added
** Natural Gas delivery charges are included
† Wood has been listed twice as Portage & Main Outdoor Water Furnaces burn 1/3 to 1/2 less wood than other outdoor boilers or stoves.

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9. Average Heat Values in Various Species of Wood

Species Density of Dry Wood (lbs/ ft3) Weight of Dry Cord (lbs) Heat Value of Green Wood BTUs/Cord (millions) Recoverable Heat Value of Cord Dry Wood BTUs/Cord (millions) Units needed to produce 1 million BTUs
Apple 48.7 4,100 26.5 18.55 0.054
Aspen 27.0 2,290 14.7 10.29 0.097
Balsam Fir 26.3 2,236 14.3 10.01 0.1
Basswood 24.8 2,108 13.5 9.45 0.106
Beech 44.2 3,757 24.0 16.80 0.06
Black Ash 35.2 2,992 19.1 13.37 0.075
Black Spruce 29.2 2,482 15.9 11.13 0.09
Box Elder 32.9 2,797 17.9 12.53 0.08
Cherry 36.7 3,121 20.0 14.00 0.071
Cottonwood 24.8 2,108 13.5 9.45 0.106
East. Hophornbeam 50.2 4,267 27.3 19.11 0.052
Elm 35.9 3,052 19.5 13.65 0.073
Hackberry 38.2 3,247 20.8 14.56 0.069
Hemlock 29.2 2,482 15.9 11.13 0.09
Hickory 50.9 4,327 27.7 19.39 0.052
Jack Pine 31.4 2,669 17.1 11.97 0.084
Norway Pine 31.4 2,669 17.1 11.97 0.084
Paper Birch 37.4 3,179 20.3 14.21 0.07
Ponderosa Pine 28.0 2,380 15.2 10.64 0.094
Red Maple 34.4 2,924 18.7 13.09 0.076
Red Oak 44.2 3,757 24.0 16.80 0.06
Sugar Maple 44.2 3,757 24.0 16.80 0.06
Tamarack 38.2 3,247 20.8 14.56 0.069
White Ash 43.4 3,689 23.6 16.52 0.061
White Oak 47.2 4,012 25.7 17.99 0.056
White Pine 26.3 2,236 14.3 10.01 0.1
Yellow Birch 43.4 3,689 23.6 16.52 0.061

The type of wood burned, whether hardwood or softwood, is important for the heat value and the energy efficiency.

Hardwoods have less resin and burn slower and longer. Softwoods burn quickly. In addition to the type of wood, the seasoned length of the wood influence on the fuel efficiency. Seasoning the wood refers to the allowed drying time before burning.

Moisture reduces the woods fuel value and wood needs to be dried at least 4 to 12 months before used. For best results store wood under a roof to keep wood at 20% moisture.

Note that in the table above 1 cord = 85 ft 3 is used between to convert between the "Density" and "Weight of Cord" column. Be aware that the densities used for the wood species may vary significantly. The densities used above is for natural dried wood where the average moisture is approximately 20%.

Heat values of Cords with dry wood can be estimated by adding the green wood cords values with approximately 10%.

Recoverable heat values are calculated with a stove efficiency of approximately 65%.

The Combustion process of Burning Wood

  • Wood heats up to approximately 212 °F evaporating the moisture in it. There is no heating from the wood at this point.
  • The wood solids starts to break down converting the fuel gases (near 575 °F).
  • From 575 °F to 1100 °F the main energy is released when the fuel vapors containing 40% to 60% of the heat burn.
  • When the fuel gases have burned off and the moisture is evaporated, only charcoal remains burning at temperatures higher than 1100oF.
  • T(°C) = 5/9[T(°F) - 32]
  • 1 m (meter) = 3.2808 ft
  • 1 lb = 0.4536 kg
  • 1 kWh = 3.6x106 J = 3.671x105 kpm = 859.9 kcal = 2.656x106 ft lbf = 3.412x103 Btu

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phone: 1-306-922-1722 or 1-800-561-0700 Fax: 1-306-922-1662
Address: R.R. 5 Site 16 Comp 114, prince Albert SK, S6V 5R3
Contact: bmartin@sasktel.net

The highly efficient Portage & Main Outdoor Water Furnace, with industry's best warranty, can provide 100% of heating requirements. Also known as outdoor wood boilers, yard furnaces, outdoor hydronic heaters, wood boilers, etc. models are available to heat homes, multiple buildings, greenhouses, shops, hot tubs, pools, domestic water and more. They easily adapt to new or existing forced air and hydronic heating distribution systems. Portage & Main Outdoor Water Furnaces have a model and size for every heating need-- residential or commercial. Portage & Main Heating units are being proclaimed as "Best boilers ever" by the consumers.

Copyright 2005-2011 by Portage & Main Outdoor Water Furnaces.