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Here are some of the most common questions we are asked. Click on the links below to find answers to your questions. Or visit the Series specific pages to learn more about a particular model.

Changes in the Industry

As many of you now know new EPA regulations on woodburning stoves were put in place in 2015 and another lower emissions level came in in 2020. A lot of changes have happened and there seems to be confusion on what the regulations are.

A brief history:

Until 2015, wood furnaces were only regulated at a state level. A patchwork of various state regs existed, mostly in the northeast and far west. Over the years the EPA has received pressure from various groups pushing environmental and health concerns related to wood smoke. A lawsuit was brought by several states and health groups forcing the EPA to regulate wood furnaces at the federal level using it's authority under the Clean Air Act.

In response, the EPA issued new standards that require emissions testing on all new residential wood burning furnaces. Existing units are grandfathered in. This regulation affects all residential wood furnaces manufactured after May 15, 2015. After May 15, 2020 all new wood stoves must meet the 2020 standard. Coal, commercial and ag-biomass furnaces are exempted. This ruling not only applies to outdoor furnaces but also regulates indoor wood stoves, pellet stoves- basically any new wood heating appliance.

Some states (Virginia included) have passed legislation prohibiting state officials from enforcing this law. However, this does not change the law in any way and it can still be enforced from the federal level. Some manufacturers seem to be ignoring these federal regulations and unapproved wood furnaces are out there if you shop around.

HeatMaster SS has prepared for this years ago by putting in a very sophisticated in-house test lab. Constant R&D is now the norm and new products will continue to be developed.

The G series line of furnaces is HeatMaster's answer for 21st century wood heating. The G series units easily passed emissions testing, are very low maintenance, and burn half the wood of a traditional outdoor furnace. The efficiency gain of a G series unit is very impressive.

Also HeatMaster's conventional grated models can continue to be sold for coal use and non-residential installations. Parts for repair work on existing furnaces will still be available so no customer will be left "hanging". HeatMaster SS is here to stay and will be developing new innovative furnaces in their in-house test lab as time goes on.


How quickly will an outdoor furnace pay for itself?

With gas or oil heat, it's pretty simple to calculate. Look back over your fuel bills and do the math. With a heat pump, it's a little harder because you don't know how much of your bill is going to heat your home and how much to appliances, lights etc. However, if you look at a month like May or October where you are doing little to no heating or air conditioning you'll be pretty close to what your bills will look like with an outdoor furnace. Remember neither of these methods factor in the savings on hot water which could be quite a bit more for a family.

Comparing your cost of heating to the cost of a loan to pay for an outdoor furnace (typically $1-200/month) often makes a wood heating system a no-brainer.
Most people can expect to pay it off in 2-5 years, depending on your heating costs. Buying firewood lengthens the payback period considerably. A better option might be to get a local logger to dump a load of wood that you can cut up yourself. That's what a lot of firewood sellers do so why not eliminate a middle man?
Several other things to consider: No more thermostat wars between the bill-payer and the kids! Unlimited hot water means the last person to get a shower, gets the hottest shower, and it doesn't matter how many loads of laundry you do in a row.  And with a outdoor furnace, the air coming from the duct is much warmer than with a heat pump.

What types of heating systems can an outdoor furnace be tied into?

Basically any type of forced air system (heat pump, gas or oil furnace, electric forced air) can be adapted with a water to air heat exchanger mounted in the duct. Hot water (boiler) systems are usually heated with a flat plate heat exchanger. An electric baseboard system will not adapt to an outdoor furnace and would need a new forced air, infloor heat or boiler system installed. Give us a call and we can discuss your needs or to schedule an appointment to look at your house.

Will my existing heating system still work?

Normally the existing heating system and water heater is not disabled and will still be there as a backup. Most systems can even be wired to switch over automatically so there is no risk of a cold shower or chilly house. A properly installed furnace is very easy to use.

I don't own any woodland. Is an outdoor furnace still a good idea?

Burning a furnace without owning at least 5 or 10 acres of woodland just means you need to think ahead a little more. Most of the time there is an almost unlimited supply of free wood in the hot summer months. Check on Craigslist, talk to your neighbors, drive around after a storm- use your imagination. Help your neighbor clean up after a high wind and they'll tell other folks. Remember, you can burn wood that no one else wants like pine and poplar. Check with local sawmills, loggers, or any busness that uses wood. Take a vacation in West Virginia and pick up a ton of coal on the way home if you have a grated unit. Fuel is out there if you look for it.

Why don't you recommend installing a HeatMaster furnace indoors?

We have been asked many times why we do not install HeatMaster SS furnaces indoors. At first glance it looks great- no snow or rain to deal with, fuel and furnace in one convenient location.
What we are experiencing is that many insurance companies will refuse to insure anyone that has a wood burning furnace and the fuel in the same building. They have a good reason. One careless moment- some spilled ashes near the wood pile, a firebox door left open by a neighbor, a coal dropped on the floor and rolled underneath the furnace out of sight, you name it- and you've got a real problem.     
However, a furnace installed outside with at least 10 feet of nonflammable space (concrete, gravel, pavers)around it is very safe. Even if a live coal does drop out of the fire box, there is nothing to catch on fire.

The G series models are UL rated to put in a shed or shop. But the concept of keeping fuel away from flame still applies.
I've been told "well, my insurance company doesn't know that my furnace is indoors so I can do what I like"...... My response is well, fine, but you don't really have insurance now.

Our advice is install the furnace outdoors. Do not allow weeds, dry grass, sawdust, or debris to accumulate near the unit, and place your woodshed 10-15' away. Insurance companies are satisfied, your wood stays dry, the smoke from the open firebox can easily vent away and you can duck inside the shed during a sudden downpour if need be. Access for service work is also much easier with space around the unit.
It basically comes down to the fact that we want you happy and most of all, safe. No surprises, no headaches. Can indoor installs be done safely? Yes. But wood shed fires happen.

I personally was asked to provide photos of my furnace to my homeowners insurance. Thankfully it was installed outdoors with clear space around it and all was well. We want you to be able to do the same.

Why are so many people pushing the 'burn only dry wood' thing?

Years ago the normal method of slowing down the burn rate to make a load of wood last overnight was to load the stove with green wood. Studies now clearly show that the emissions from a wood stove can increase to 10 times the normal rate when very wet or green wood is burned. Most of these emissions are burnable and means the efficiency is terrible during at least the first half of the burn cycle (till the wood dries out). And obviously pumping more wood smoke into the air is not good either.
Wood stoves are slowly becoming cleaner, but to my knowledge no wood burning stove will burn cleanly with a load of completely green wood. Even the new EPA certified units will tend to have more creosote problems and  difficulty gasifying and 'reburning' with moisture content above 40% And though a regular outdoor furnace can burn green wood, it'll burn a lot better with dry and save you time cutting wood. The number one cause of excessive smoke is high moisture wood. The good news is that with any furnace that has an automatic draft there is no need to try to control the burn by adding wet wood. All HeatMaster furnaces have dampers that only allow air onto the fire when it is needed to raise the water temperature.

So, some pointers on drying wood:
-Get it up off the ground. It is extremely difficult to dry a piece of firewood that is laying against wet earth.
-Protect from rewetting from rain and snow. Ideally with a wood shed that allows ventilation. Tarps will do in a pinch, but who wants to dig wood out from under a snowdrift? I tend to get lazy and not cover at all if I'm using a tarp.
-Sun and wind are your best friends in speeding up the drying process. Think a south slope out in the open.
- Get a cheap moisture tester on The proper way to test is to split a stick of wood and test the center. You'd be surprised how wet some 'dry' looking wood is on the inside.

And if you're really serious about drying your wood fast, there are all kinds of places online giving plans on solar wood kilns. From what I've read you need to have a triangular shed with the 45 degree angle facing south, cover the angle with a double layer of clear plastic or plexiglass, insulate the walls with styrofoam and paint it black on the inside. Put a fan inside to stir the air to speed up the drying process, and ventilate only enough to stop it from sweating inside.  Theoretically you could heat it up with your outdoor furnace too!

Seriously though, burn dry wood. You'll use a lot less of it and your neighbors will thank you.

I see a lot of debate on the web about stainless v. mild steel. What's the truth?

There are basically three steels used to build outdoor furnaces- mild steel, 304 Stainless and 409 Stainless. The truth of the matter is that it is possible to build a good outdoor furnace out of any of these steels. The type of steel used determines to some extent the design and durability of the unit. Each has it's unique strengths and weaknesses and one manufacturer will advertise against another, using one side or the other and sometimes not giving the whole picture. This has confused much of the general public and is in our opinion not beneficial.


Mild steel has very good heat transfer and is easy to weld and bend. Most manufacturers use some form of mild steel, typically 1/4" thick, sometimes less. The weakness of mild steel is that it has no corrosion resistance. Moisture in any part of the furnace will cause that area to corrode quickly, in many cases becoming thin enough it is impossible to repair.  I've seen it too many times. Water treatment is critical, and the furnace must be designed to not condensate anywhere. Also rain water must not be allowed to enter the furnace during the summer months. Down draft gasification furnaces are particularly corrosion prone with mild steel because of the condensation that forms in stagnant air in the upper part of the firebox and in the chimney due to low exhaust temperatures.

Some manufacturers have used some form of stainless at their "trouble spots", reducing the condensation corrosion, with the rest being mild steel.

Mild steel will perform well in the short term (which is why they sell) but negligence on the part of the homeowner or poor design can ruin a unit in a few years. We have seen mild steel units last 3 years or 20 depending on the design of the unit and the care it received. Most older mild steel units have been welded on at some point. Again, the key with mild steel is no moisture and having properly treated water.


304 Stainless is used by a few manufacturers, probably because of it's increased corrosion resistance over 409. 304 is much more forgiving of running the unit with no water treatment (although it is still beneficial). The downside of 304 is that it is very expensive, has the poorest heat transfer of the three, and will not tolerate being run low in water (causes warping and cracking). 304 has a very high thermal expansion rate and the design of the furnace must take that into consideration (no square corners to warp and crack etc.). Absolutely never run a 304 unit low in water and it should last. All the "spider cracked" stainless furnaces that I have seen talked about online are 304 SS. But as we will discuss under 409, there are other types of "cracking".

409 Stainless is used by a few manufacturers (including HeatMaster SS) because, although it has it's weaknesses, in the total picture it's strengths add up better than the other steels. It has good heat transfer, good corrosion resistance (we have never seen wet ashes or condensation eat out a 409 unit), can handle very high temperatures (it is extremely rare to see a 409 water jacket split open from low water/overheating), and costs a lot less than 304.
It's weaknesses are that it is more difficult to manufacture than mild steel (requires more experienced welders, is much harder to cut, etc.)  I have never seen spider cracking on any 409 unit regardless of the brand. The "cracked" 409 units that I have seen were welds that separated because of poor welding or overheated material beside the weld. This is why HeatMaster SS is extremely careful when hiring and training new welders. 409 also requires water treatment to prevent pitting from sludge buildup and electrolysis. Heatmaster SS does free water testing for life on all their units.


Beware of manufacturers marketing themselves as "stainless" with only a stainless firebox. The water jacket being mild steel hidden by spray foam. This is misleading but it is happening.

In the past we've sold units made of all three steels. We have had much fewer warranty issues with 409 units which is why we are firm believers in 409 and HeatMaster SS.  

How do I research a particular dealer or brand of furnace? Everyone claims to be the best.

There are many factors to consider when deciding on a particular dealer or brand of furnace. Here are a few of them.

1. References. Testimonies of real people you can talk to face to face are probably the most reliable information you can get. Find a customer that is happy with his furnace and dealer and you're much closer to making a good choice.

2. Talk to the dealer. How knowledgeable is he? What is his relationship like with the  manufacturer? Does he get support and how do they cover warranty issues? How long has he been in business? What does he know about furnace installations and how many has he done? What training has he had? No matter how great the furnace is, it can't heat your home if it's not hooked up correctly. Does he listen to you or just try to sell, sell, sell? Do not let a "limited time offer" cause you to go against your gut feelings.

3. Web research can very useful. It does take some time to narrow down to the best two or three models. 

Beware of a company that repeatedly claims to be the best without giving any real information. Forums can be very useful, but keep in mind you will get opinions from anyone, regardless of their knowledge or experience, be prepared to tune out a few individuals.

There are a few complaints online about even a reputable brand, but stay clear of a brand of furnace that has complaints on every forum. If the furnace works well there will be positive reviews in multiple locations online.  It can be very interesting to do a google search of a brand name. Usually if there is a problem with a particular model it will show up somewhere.

Also the web is useful to see if the company has a full line of EPA certified furnaces. It is no longer realistic for a furnace manufacturer to stay in business without offering a line of compliant models.

4. Installation is key to making a furnace work properly. A good furnace can never overcome a poor installation. Talking to an experienced installer can really help. A small, easily fixed mistake by an inexperienced installer can create a lot of unnecessary headache.

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