Build a wood stove build-it-yourself BIY advice
Build a wood stove from a scrap barrel
I want to build a wood stove with a pretty 50 gallon metal drum. Make a baffle box out of steel with a 10 cm gap to increase the heat output. I might use an old catalytic converter from a truck as an option. No policeman is going to look for you if there is some smoke and this would be a great heat source.
Review of the rocket stove
Your barrel stove idea to build a wood stove is nothing new: similar designs have been around since….. well, since barrels. I’ve seen several variations of your double-baffle idea over the years, and while incorporating baffles in the design might improve the burn of barrel stoves a bit, I hope you realize that you’re never going to build a stove that even approaches the efficiency of an approved design (I’m going to assume that your idea of incorporating a catalytic converter out of a truck is not something you’ve actually tried, because there’s no way that would ever work).
The point is, certified approved designs are better than homemade stoves in several respects:
- They heat the same area while burning about half the fuel (saves half the cutting, splitting, hauling, not to mention usage of the wood resource).
- Their stay-clear viewing windows allow you to ensure your fire is burning properly from across the room (prevents smouldering, assures utmost burning efficiency).
- They cut the formation of creosote in the chimney by about 90% (less frequent need for sweeping, less chance of having a chimney fire).
- If you ever do have a fire, your certified stove and installation ensures that your insurance company will pay your claim. (Seen many sad clients who build a wood stove house fires).
- They are MUCH kinder to the environment, as they exhaust the only 1/20th of the particulate emissions into the airshed as not approved stoves. Since our generation has finally come to the realization that protecting the environment is everybody’s business, deliberately burning a homemade smoke dragon like you describe could be looked at like tossing your empty drink cans out of your car window.
My own self-welded stove
I don’t like any of the wood stoves you sell or any of the wood stoves I’ve seen anywhere else. They are all too small, they all have such dinky little viewing windows. I’m pretty handy with as a welder and want to build my own wood stove to heat my 120mt2 home (which is very well insulated). The stove I have in mind would need to meet the minimum certificate emissions standards without a catalytic converter and I have an old firebox like the wood stove my Dad used to have, which is big enough to hold 76cm pieces of wood, or even bigger (I cut my own wood, and don’t want to have to whack up small pieces). I also want to have a larger glass door than the ones I see on manufactured wood stoves. I’ve been all over the web and you seem to know your stuff. I feel like if I just understood the theories I could weld something up and make modifications to it until I get it to work right. Can you tell me the basics to build a wood stove as I need to know to design this thing? Also, if you have the time or any tips you care to share that might be helpful. It’s getting cold outside!
Problems with your own build a wood stove concept
Let’s start with a basic overview of how non-catalytic wood stoves clean up the smoke emissions. The concept is pretty simple: in order to meet standards, you’ll need to create a second fire inside the wood stove’s firebox to reburn the exhaust from the primary fire. The secondary burn area in an approved stove is usually located at the top of the firebox. Designed in such a way that the exhaust from the fire must pass through it on the way out the chimney. In operation, the wood exhaust ignites inside the chamber, creating a 600+ degree flame (much hotter than the wood fire below) which burns up approximately 90% of the smoke particles as they pass through it.
In order to fire off your secondary burn, three things must be present at the same time and in the right amounts: fuel, heat and oxygen. The fuel part is easy: it is the smoke from the primary fire. Likewise the heat: ceramic blanket insulation used above the chamber to trap the heat from the fire below and ensure light-off temperatures. The oxygen part gets a little tricky: since the primary fire has consumed most of the oxygen available in the firebox, preheated air must be introduced into the reburn area so secondary combustion can occur. Your design challenge will be to figure out a way to preheat the secondary combustion air to the right temperature and cause it to be drawn into your secondary burn area in measured quantities that automatically adjust with the draft control that supplies air to the primary fire, keeping in mind that the secondary flame must keep burning and cleaning up the exhaust even when the primary draft control is at its lowest setting.
Tip: Over 1000 wood stove manufacturers worldwide have gone out of business in recent years as a result of being unable to engineer a stove that would burn clean enough to meet emissions standards. The sad fact is, unless you are an exceptionally talented thermal design engineer with a background in wood combustion and lots of time and materials for prototype testing, your BIY secondary burn design probably isn’t going to work.
Next, let’s look at wood stove viewing window basics. Early attempts at adding viewing windows to wood stoves were miserable failures, as the windows turned black almost immediately from contact with the wood smoke. Since it is kind of silly to go to the expense of incorporating a viewing window if you can’t see through it, wood stove manufacturers soon learned to incorporate an “airwash” in the design of the stove, taking a portion of the incoming combustion air, preheating it, and directing it across the inside surface of the window to keep the smoke away. Airwash designs are a little tricky, as they require building the necessary preheating chambers into the design of the stove and then providing a means to direct the airflow across the inside window surface without adversely affecting burning efficiency. When you build a wood stove yourself most people end up eliminating the viewing window totally because as it is extremely difficult to have a clean glass viewing fire.
Tip: Manufacturers know that a big view of the fire will appeal to wood stove buyers, and make every effort to provide the largest viewing window that can be kept clean by the airwash system. Pacific Energy where leaders in the industry. As you build a wood stove, modify and retest your stove with various airwash delivery systems and various sizes of windows, you’ll find that there’s a limit to how big the window can be and still be kept clean by the airwash. You could save yourself a lot of futile effort by resigning yourself to a viewing window that is about the same size as the ones you see on manufactured stoves.
Finally, let’s tackle firebox sizing. Wood stove manufacturers know that people who buck up their own fuelwood want fireboxes that can hold larger pieces of wood, because cutting wood is hard work, and larger pieces mean fewer cuts. So why, in recent years, have these manufacturers been making their fireboxes SMALLER, instead of larger? In a word, heat. Too much heat. Remember that 600+ degree burn in the secondary burn chamber? Your Dad’s stove didn’t have one of those. If it had and was as big as you describe, he wouldn’t have been able to stand the heat long enough to go into the house, let alone get close enough to the stove to add one of his 70cm chunks of wood to the fire.
Tip: Our highest output wood stove, the Pacific Energy FP30, has a firebox measuring just 50cm x45cmx 33cm (76 litres), yet generates up to 29 Kw per hour (enough to heat a 275mt2 house). If you do manage to design and build a reburn chamber that works and wants to heat your 120mt2 house without blasting your family out into the yard, you’ll want to plan a firebox that will accommodate your 70cm logs after they’ve been cut in half. This won’t cause you any extra labour at cutting time because if your reburn design works, you’re only going to burn about half the wood your Dad did to heat the same area.
Here’s something you didn’t ask about, but need to know: Country and district laws prohibit installation of any wood burning heater that isn’t listed and certified. Obtaining this approval is not practical for a single stove: even if you were able to build a stove that would be safe enough and clean-burning enough to pass, you’d be out about twenty grand for the safety and emissions testing. If you were to go ahead and install your home-built wood stove without listing labels from the test labs, you most likely wouldn’t be able to get a permit from your Authority to install it. In the event of a fire claim, the insurance adjuster might notice the lack of listing labels or ask to see your installation permit, at which point your coverage would probably hit the fan.
To sum up, the most likely product of your efforts to build a wood stove will be an illegal, wood-gobbling, creosote manufacturing smoke dragon with a viewing window you can’t see through. And no insurance coverage in the event that this monster burns your house down.
I just read your page concerning the gentleman that wanted tips on how to build a wood stove. I have to say I appreciate the complete, well thought out and intelligent response. You could have just said it’s too hard you cannot do it and it would be illegal, In my mind a worthless, frustrating answer that would indicate we are all too stupid to understand a thorough explanation.
Thank you for taking the time to give a very good answer to a relevant question !!
Thanks for the kind words! They used to say, “Asking a question is not stupid. Having the answer and not sharing it is stupid.”