FAQ: Outdoor Wood Burning Furnace Questions and Answers

FAQ Question Categories:

  1. General Questions
  2. Why Hawken Furnaces are Best
  3. Furnace Installation
  4. Furnace Operations
  5. Maintenance
  6. Warranty
  7. Customer Satisfaction
  8. Impact on the Environment

1. General Questions

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

Absolutely! We will assess your heating requirements and provide you with the size of outdoor wood furnace that meets your needs.

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

It is very simple. Although an outdoor furnace is like a boiler, your home does not need to have hot water heat – the Hawken furnace system will easily interface with any forced air heating system. The heat from an outdoor wood furnace fire is transferred to water that is stored in the system. This hot water is pumped from the outside wood furnace to the home and back to the furnace through an underground insulated pipe. A heat exchanger inside your home or building takes the heat from the water and delivers it to your home.

I have a forced air heating system with ductwork and registers. Will a Hawken furnace work at my house?

Yes. The Hawken furnaces are designed to interface very easily with any forced air heating system. This is the most simple of all installations. A water-to-air heat exchanger (which looks like a car radiator) is very easily placed in your furnace plenum and then your furnace operates in “fan-only” mode to blow very warm air throughout your home without burning any gas. See the "How It Works" page of our website for more details.

Can I heat more than one building?

Yes. The Hawken 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?

Many things can be efficiently heated with an outdoor wood furnace other than your home: Domestic hot water, hot tubs, pools, garages, barns, workshops, any commercial building, and other commercial uses including greenhouses and dairies.

How large of a furnace do I need?

Your Authorized Hawken Rep will assist you with this decision. Factors to consider include square footage, ceiling heights, quality of insulation, extra buildings, etc. Generally, our HE-1100 is considered the “one-building model” and will heat any normal to large sized home. Our HE-2100 is considered the “two-building model” and will heat any two buildings up to 10,000 square feet. For those applications requiring heat for more than 10,000 square feet, we use multiple furnaces.

2. Why Hawken Furnaces are Best

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

The savings are enormous. Please call us for a custom analysis of the savings you will experience, since this will depend upon which fuel you currently use for home heating, and a few other factors. As an example, if you currently heat your home with propane, you can expect to reduce your heating costs by about 75% since wood is less than one-fourth the cost (per BTU) of propane. If you have your own wood source, your savings will be even greater.

Why is the Hawken Outdoor Wood furnace superior to all other alternatives?

Don’t take our word for it. Please ask for your FREE copy of the Energy Industry Comparison Report that compares the Top 10 outdoor furnace manufacturers based on how well they meet the industry standards set by the Canadian industry experts at www.outdoorwoodfurnaces.org. These industry standards comprise an outdoor furnace “Buyers Guide,” which is also available free of charge from Hawken Energy. This “Buyers Guide” explains 36 critical factors that should be considered before purchasing an outdoor furnace.

How long will the furnace last?

Our furnaces have a 20 year limited warranty. With proper maintenance, this high-grade structural plate steel furnace will deliver many years of trouble free service.

Why do Hawken furnaces have round fireboxes?

The round, barrel-shaped firebox design has passed the test of time. No other firebox design has been tested and proven more effective. Beginning with the original steam locomotives, the round firebox design provides better heat transfer, and higher efficiency based on the way fire naturally burns. This design also has fewer welds, which means greater strength and longevity.

What kind of insulation does the furnace have?

Hawken furnaces use high grade R-30 8" thick fiberglass insulation. This will not crack and lose heat like cheap spray-on foam.

How thick is the steel?

The firebox and water jacket are made of the highest grade one-quarter inch structural plate steel.

3. Furnace Installation

How complicated is the installation?

Installation is simple. Many owners do their own installation using our new Owners Manual. Or, if you prefer, we can handle all or part of your installation through our specially trained and approved installers.

Can I install the furnace myself?

Yes! You need to be able to sweat pipe and have access to a few necessary tools. Hawken has a complete Owner’s Manual and assembly instructions that make the process simple.

How do I get my furnace located where I want it?

Hawken Reps have special trailers that can place your furnace in any location where a truck can be driven. Please advise your Hawken Rep of any special needs such as fences to be moved or unstable ground.

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

No. The insulated underground pipe does not lose heat and is buried about 2-1/2 feet under the ground. You can place the furnace anywhere you desire and the only additional cost is for the insulated pipe and tubing. Some installations have been made in excess of 250 feet. If 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?

All Hawken furnaces are designed to run on 110v electricity. Many homeowners add an additional breaker to their box for the outdoor furnace.

How deep should the electric line be buried?

In many areas, codes require that electric lines be buried at least two feet deep. Please consult your local codes. The electric line can be buried in the same trench as the underground pipe.

Is a chimney cap required?

We recommend chimney caps for the following reasons: 1. The clover leaf design of the chimney caps keeps rain out of the furnace; 2. they reduce heat loss, particularly in high winds; and 3. the chimney cap works as a spark arrester.

Is a cement pad required?

NO! All Hawken furnaces can be installed on cement header blocks (similar to patio blocks). This saves considerable time and cost, and gives you the flexibility to easily move your furnace in the future.

4. Furnace Operations

How complicated is it to operate and maintain an outdoor wood furnace?

Thanks to new technology, the Hawken Outdoor Furnace works automatically. When heat is needed, a fan automatically turns on and provides fresh air to the boiler 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. Therefore, operation of the Hawken Outdoor Furnace is extremely simple. All you need to do is add wood once or twice daily and remove ash.

How often do I need to add wood?

Less often than you would expect! Naturally, this 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 fill 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?

You should only purchase a furnace that has a “forced air” draft blower fan. Do not make the mistake of purchasing a “natural draft” furnace which has much lower efficiency, and will only burn certain types of highly processed wood. Natural draft furnaces only have a small door that opens allowing air to feed the fire when needed. However, since this system does not control the amount of air entering the firebox, the fire takes a long time to recover, and then burns uncontrolled which is inefficient and harmful to the system. Furthermore, natural draft furnaces will not burn large pieces of wood, or green wood.

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?

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

How is the ash removed?

Ash removal is done the same as all other furnaces – with a garden shovel. In most cases this is only required once every 3-4 weeks.

Some furnace brands boast a complicated grate and auger system. Hawken is proud NOT to offer this source of frustration. Augers don’t work because they drill a core in the ash, then requiring a shovel to remove the ash. Unnecessary grates complicate the process further. We have tested grates and augers and have found that they are only a burden.

How often will I need to remove ash?

In most cases, ash removal is only necessary once every 3-4 weeks.

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

By moving the furnace fire out of the home, you greatly reduce any risk of fire. Normally you will locate the outdoor wood furnace at least 30 feet from your home or other buildings. A chimney cap spark arrester will diffuse sparks.

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

Yes. Your internal furnace becomes a backup and this inside furnace would come on if the outside furnace were stopped. Otherwise, the inside furnace will not ever operate. The same is true of your hot water heater – it just becomes a storage tank.

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

No. With 180 degree water, the system will never freeze as long as the outdoor furnace is running and the pump is working. Even without wood, the furnace will absorb some heat from the indoor loop further preventing freezing. The outdoor furnace is highly insulated which minimizes heat loss, even in the coldest weather.

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

This depends upon how long you plan to be away, and how cold the weather will be while you are gone. If you will be away for a weekend, you can turn down your indoor thermostat, fill the furnace full of wood and turn off the draft fan, and enjoy your weekend away.

If you will be away for more than a weekend, you should still turn down your thermostat indoors, but you should make arrangements to have a friend or neighbor feed your furnace. If you will be away for an extended period of time during the winter, you may want to use antifreeze. As always, please follow all manufacturer's guidelines.

Should I use antifreeze?

There are many benefits to using antifreeze – in addition to freeze protection (which is a very small risk in normal conditions), antifreeze also provides some corrosion resistance and may increase the life of your pump. The downsides to using antifreeze are as follows: 1. It is very expensive, 2. it needs to be “recharged” annually, and 3. it reduces efficiency of heat transfer up to 13 percent.

For customers who wish to use antifreeze, Hawken recommends the environmentally-friendly propylene glycol similar in formula to Dow Frost. Be sure to follow the anti-freeze manufacturer’s recommended percent mixture to give you the freeze protection you need.

What happens if we have a power outage?

In a power outage, most home heating systems will not operate because they require power. If power outages are common in your area, we recommend that you install a generator.

Is a Hawken furnace pressurized?

No. Most all outdoor wood furnace systems are not pressurized. All Hawken furnaces are non-pressurized. When we connect to a home that has a pressurized boiler, we transfer the heat from the outside furnace water to the inside pressurized water by using a plate heat exchanger.

How does the Hawken furnace heat my domestic hot water?

Since 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. These plate heat exchangers enable homeowners to enjoy an endless supply of hot water.

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

It is a very simple connection through a plate heat exchanger which transfers heat from the outdoor wood furnace to your home. This keeps your pressurized system safe, and provides tremendous efficiency which helps you achieve big savings.

Do you have to add water? How?

Since outdoor furnaces are non-pressurized and open to the atmosphere, water can evaporate from the system. We recommend adding water once monthly. With the Hawken system, this is easily accomplished by opening your fill valve in your basement. Other furnace brands require their customers to haul a hose out to the furnace to add water on a regular basis – even during the coldest months of the winter.

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. A small amount of water is drained once per year to clear out any sediment, and to take a water sample for testing. See your Owner's Manual for more information.

What is the proper Ph level for the water?

The new Certified Labs chemical and water sample test will satisfy any Ph requirement.

Can Hawken furnaces burn corn?

Although there has been much excitement about burning corn, shelled corn is a very difficult fuel to use. So far, no manufacturers have found an effective way to burn shelled corn in an outdoor furnace, except in industrial applications. Many manufacturers have introduced corn burners to customers who have been disappointed to learn of the difficulty these units have in maintaining normal operation.

The biggest difficulty of corn burners is starting the fire. Once corn stops burning, it is very difficult to restart (unlike wood that will smolder for days until fed oxygen again). Since outdoor furnaces must cycle on and off based on heat requirements, corn burning outdoor furnaces must be able to restart the fire after cycling off. Currently, no outdoor corn burner exists that addresses these issues.

Hawken has tested various corn burners and has found several problems exist with them. First, given that corn is difficult to ignite once cycled off, we found that several corn burners will attempt to feed more corn into the fire to solve the problem. Unfortunately, since the corn is not burning, the result is that corn is quickly fed to the burn chamber until the hopper is empty. Second, some corn burners do not have proper fuel feed designs and fire can creep up the auger and burn up the entire hopper full of stored corn. Third, we found a corn burner whose design did not have the water jacket completely surrounding the firebox. A continuous run study proved disastrous as the control box became cherry red!

One manufacturer recently introduced an add-on kit that converts a wood boiler into a corn burner. Not only is this system excessively costly, it is also highly inefficient given that the dynamics of heat transfer from corn fuel are far different than those from wood fuel.

Although the use of shelled corn as a fuel is attractive since it appears to require less work than burning wood, it is actually anything but. All corn burners require daily maintenance and cleaning, and the corn fuel must be perfectly dry (less than 15 percent moisture) to avoid “gumming up” the system.

Hawken Energy only sells products that are proven and reliable. Unfortunately, outdoor corn burning furnaces have not yet proven that they can operate reliably and without continual supervision. Many companies selling corn burners have had to disguise their serial numbers to make them appear to have sold thousands of them when, in fact, they have only sold a few and the initial customers are guinea pigs. One company has had to recall all of the units they sold.

Hawken remains hopeful that our research efforts will yet uncover the ideal design for an outdoor corn burning furnace, but our commitment remains that we will not sell a product that is not proven to be reliable. Our initial studies have shown that corn on the cob burns quite well in our wood burning furnace, but more research is yet required.

5. Maintenance

What are the regular maintenance items?

Hawken furnaces only require a few simple maintenance items: 1. Check water level and add water to the system when needed by opening a valve for a few seconds; 2. Periodically inspect and clean the water filter by opening the filters by pass valve and closing the two valves on both sides of the filter to discharge the filter. On occasion, disassemble the filter and flush it out. 3. Rake and remove ash as needed – generally once or twice per month depending upon the wood you burn. See Owner’s Manual for more details.

Do Hawken Furnaces require any creosote maintenance?

No. Unlike other outdoor wood furnaces, the Hawken unit does not require any creosote maintenance because its superior design reduces creosote formation. Any creosote quickly burns off and is not harmful to the high grade of steel in all Hawken furnaces.

6. Warranty

How long is your warranty?

Many outdoor wood furnace companies are embarrassed of all the loopholes and tricky legal language they use. For example, one company boasts a "25-Year Limited Warranty," but when you read their fine print, they limit their coverage to only 10 years on the firebox! The firebox is the most critical component. The Hawken "Industry Best" 20-year warranty does not limit warranty coverage of the firebox – the firebox is covered for the entire 20-year warranty period.

A warranty is only as good as the company that stands behind it. We back our products not only with the "Industry Best" Hawken 20-Year Warranty, but also with the commitment from Hawken to stand behind your entire furnace package – including all parts and components. You will never find a Hawken customer who is unhappy that they purchased a Hawken furnace!

See your Owners Manual for complete warranty details.

7. Customer Satisfaction

Who is Hawken Energy?

Hawken Energy is dedicated to providing cost-saving heating solutions using outdoor wood furnaces. Hawken markets in much of the United States. Hawken locates and trains Reps certified in the sale and proper installation of this equipment.

Where can I get more information?

The Hawken Energy team consists of outdoor wood furnace experts who are capable of answering any questions you may have. Please do not hesitate to call us at (888) Log-Burn, or (888) 564-2876, or send us an email to Info@HawkenEnergy.com.

8. Impact on the Environment

What impact does burning wood have on the environment?

Wood is an environmentally friendly resource that reduces greenhouse gases and produces no increase in carbon dioxide – this cannot be said for fossil fuels. Also, wood as a fuel reduces our nation’s dependency on foreign oil.

Responsible companies in this industry, like Hawken Energy, only sell to customers who either live in rural areas, who properly vent smoke, or who use proper emission control devices. Though heating with wood may sound old fashioned, modern wood-burning appliances are anything but. The use of emissions control devices can reduce 90 percent of smoke emissions.

The world is running out of fossil fuels. Experts have shown that in just a few years, the world’s inhabitants will have consumed one-half of the known fossil fuel reserves. Once this happens, fuel prices will skyrocket as fears of “running out” will become more of a reality. This prediction is based on the present world consumption; however, world consumption is expected to increase. Since solar, hydrogen fuel cells and other energy technologies are still in their infancy, wood fuel is becoming the fuel of choice for many homeowners.

Is wood a “Renewable Resource”?

Yes! Wood is a plentiful renewable resource that has been safely used as a fuel longer than any other fuel – since the beginning of history. A “Renewable Resource” means that it can be restored and replenished by nature in a period of time that is compatible with our human use. The heat released from wood is actually stored energy from the sun-released when consumed in a wood burning boiler.

Why doesn’t wood add greenhouse gasses to the environment?

Wood burning is completely safe in terms of “Greenhouse Gasses” - All fuels produce carbon dioxide, the primary greenhouse gas, when they burn. When the atmospheric concentration of greenhouse gasses increases, they cause the average global temperature to rise.

Wood differs from the fossil fuels - coal, oil and gas - because it is part of the natural carbon/carbon dioxide cycle. As a tree grows, it absorbs carbon dioxide from the air and stores it in the wood as carbon, which makes up about half of the weight of wood. When the wood is burned, carbon dioxide is released back into the atmosphere. No additional carbon is released because the same amount of carbon dioxide would be released if the tree died and were left to rot on the forest floor. The carbon in coal, oil and gas, by contrast, are taken from underground stores, usually from overseas, where they were deposited by nature, and released into the air without means for equal re-absorption.

When trees are used for energy, a part of the forest's annual growth is diverted from the natural decay and forest fire cycle into our homes to heat them. Firewood is a natural energy product from the forest. Burning wood actually helps reduce greenhouse gas emissions by displacing the use of oil, gas and coal.

Is there enough wood?

Yes. Wood is an abundant resource in this country that is easily sustained. Provided they are cared for and managed properly, our forests can be a perpetual source of fuel, unlike gas, oil, and coal, which are being depleted at a rate that is astonishingly faster than the millions of years it took nature to make them. Wood is affordable, renewable, sustainable, it is a secure domestic heating method, and wood is appropriate to the resources of our country.

Wood is ideally suited for human consumption since it naturally renews itself, and adds no greenhouse gasses to the environment.

Does wood burning save money over burning fossil fuels?

Yes! Per Btu, wood is much less expensive than fossil fuels – natural gas is three times the cost of wood, propane is five times the cost of wood, and electricity is seven times the cost of wood. This assumes wood is purchased, but many people have an unlimited supply of free wood.

What is the BTU value of different types of wood?

See chart below:

Heat Values in Various Species of Wood

Species Density (lbs/cubic ft) Weight/Cord (lbs) BTUs/Cord (millions) Recoverable BTUs/Cord (millions) Units needed to produce 1 million BTUs
Hickory 50.9 4327 27.7 19.39 0.052
East. Hophornbeam 50.2 4267 27.3 19.11 0.052
Apple 48.7 4100 26.5 18.55 0.054
White Oak 47.2 4012 25.7 17.99 0.056
Sugar Maple 44.2 3757 24 16.8 0.06
Red Oak 44.2 3757 24 16.8 0.06
Beech 44.2 3757 24 16.8 0.06
Yellow Birch 43.4 3689 23.6 16.52 0.061
White Ash 43.4 3689 23.6 16.52 0.061
Hackberry 38.2 3247 20.8 14.56 0.069
Tamarack 38.2 3247 20.8 14.56 0.069
Paper Birch 37.4 3179 20.3 14.21 0.07
Cherry 36.7 3121 20 14 0.071
Elm 35.9 3052 19.5 13.65 0.073
Black Ash 35.2 2992 19.1 13.37 0.075
Red Maple 34.4 2924 18.7 13.09 0.076
Boxelder 32.9 2797 17.9 12.53 0.08
Jack Pine 31.4 2669 17.1 11.97 0.084
Norway Pine 31.4 2669 17.1 11.97 0.084
Hemlock 29.2 24.82 15.9 11.13 0.09
Black Spruce 29.2 24.82 15.9 11.13 0.09
Ponderosa Pine 28 2380 15.2 10.64 0.094
Aspen 27 2290 14.7 10.29 0.097
White Pine 26.3 2236 14.3 10.01 0.1
Balsam Fir 26.3 2236 14.3 10.01 0.1
Cottonwood 24.8 2108 13.5 9.45 0.106
Basswood 24.8 2108 13.5 9.45 0.106

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