Wood Stoves with Outside Air Intake (Benefits/Disadvantages) - (Catalytic/Non-Catalytic) ?

LS123 · June 5

Greetings!

Recently saw a survey posted by @Erin Holohan Haskell about pellet stoves, I liked it because most people I know in Northwest CT have pellet stoves and wood stoves.

We already have a pellet stove (with outside air intake), and thinking about adding a wood stove. Because of the age of the house (75+ years), we would like to have a wood stove with built in outside air intake (if there are any and reasonably priced)

I have not been able to find a wood stove(s) with built in outside air intake. if anyone of you know any, please could you let me know?
I learned benefits of having out side air intakes, but if any of you know of any disadvantages using a wood stove with built in outside air intake lmk?
Also what are the benefits and disadvantages of using wood stoves with catalytic combustion ( other than they are much more expensive, burn less wood and much more environmentally friendly exhaust gases)? Is the cost of a Catalytic wood stove worth it?

please let me know ( any thoughts @Jamie Hall , @EdTheHeaterMan , @pecmsg and all )

Erin - Will there be a section for renewable heating sources like wood and pellet stoves at some point?

Thank you!

Jamie Hall · June 5

I have exactly zero experience with either wood stoves equipped with catalytic afterburning or wood stoves with an outside air intake. Having said that — which qualifies as not knowing much about them — I do have a good deal of experience with both good air tight stoves (Jotul, Vermont Castings) and non-air tight (Glenwood Parlour). The chief advantage I can see with an outside air intake is that it would reduce infiltration — but an air tight stove doesn't burn a whole lot of air, anyway, and some air infiltration into a house is not a bad thing. The chief disadvantage is going to be extra complexity and cost — and some maintenance on the gaskets. I'm not really keen on the concept of catalytic afterburners — but in some (all?) jurisdictions you have to have them now, so it's often a moot point.

The chief thing I've found over the years with wood stoves — and fireplaces, which Cedric's home has and uses — is the quality of the wood. As the song says — and some of my relatives can attest! — use hickory, ash, or oak, and don't burn green or rotten wood. You'll have little or no smoke, very little creosote (you still want to sweep that chimney, though) and a good, hot, efficient, controllable fire — even in an ancient Glenwood Parlour, which was anything but air tight!

Larry Weingarten · June 5

Hi, I agree with Jamie. A good stove with secondary air doesn't need a catalytic device, so there is less to plug up or fail. I use a Vermont Castings stove that I have hooked up to outdoor air. Even though it has a six inch flue, the intake is four inches… smaller and simpler to install. One benefit it that the air leakage into the building is happening only where you want it to. Also, the stove isn't acting like a big hole in the hose, leaking when it isn't in use.

Yours, Larry

Grallert · June 5

If I'm not mistaken, and I could very well be, some manufacturing companies are getting away from catalytic converters and have come up with different ways to achieve secondary combustion. It's been a few years since I've dug into this. With the age of your house I don't think you'd NEED direct makeup air for clean combustion but maybe that's just something you want in order to have a bit of control over the combustion air.

And Jamie hit the nail on the head. It's all about the wood. Well mostly about the wood.

Erin Holohan Haskell · June 5

@LS123, we have a category for this on the forum called Biomass.

The Alliance for Green Heat's website is an excellent resource for information about wood and pellet stoves. I enjoy their monthly email newsletter too.

hot_rod · June 5

My experience is mainly with wood fired boilers. The gasification principle allows them to run efficiently, meet or exceed emissions without needing a catalytic converter. Some sure wood stoves incorporate that principle, most come from across the pond www.wallnoefer.it is one example.

I have a Cubic Mini wood stove in my camper, made in Canada, and it has a secondary air adjustment that allows it to burn hotter and cleaner.

Marc at this site used to import a bunch of high efficiency wood stoves from Europe. Wood cook stoves also.. Looks like he focuses on bio boilers now.

Moisture meters are cheap and a good way to assure the firewood is dry.

I would duct air to the appliance even if it doesn't have a specific air connection. A grill below ducted to the outside is one way to go.

www.hearth.com is an excellent site where wood burners share experiences. Go to the forums for some good hands on experience.

Next march is the ISH expo in Frankfurt. They have a massive exhibition hall dedicated to wood, bio, and pellet burning stoves. Many are actually operating. A great place to research solid fuel burning devices.

https://ish.messefrankfurt.com/frankfurt/en/exhibitor-search.html?q=Wood%20stoves

WMno57 · June 5

Wood smoke is a carcinogen. If you can smell it, …

We have a child-like approach to safety and risk in this country.

Trains, cars, campfires, and nitrate free hot dogs* are 100 percent good.

Nuclear power, Irradiated food, GMO foods, and vaccines are 100 percent bad.

I like the smell of wood smoke by the way. But I know I'm inhaling carcinogens.

https://en.wikipedia.org/wiki/Polycyclic_aromatic_hydrocarbon#Human_health

*except those nitrates occurring naturally in sea salt and celery powder.

Jamie Hall · June 5

I wish it were a child-like approach, @WMno57 . At least with children there is an element of innocence…

There are astonishingly few compounds — natural or man-made — which are NOT harmful at some dosage or other. You mention polycyclic aromatics? Better stay from that broccoli or spinach — they're loaded with them (and all of them are carcinogens, if you get enough of them). Sunshine? Oh dear me. Melanoma!

Diprotium Oxide? Very common, and a one hundred percent mortality rate among people exposed to it.

A little realism about hazard goes a long way. About three thousand years ago, a man named David wrote this about it: three score years and ten is the measure of a man, or by strength four score, We have pushed that out a tiny bit, but… not much. What has all of our banning and Prop,65ing and warning accomplished? Um…other than terrifying a lot of people, not much.

Live a little.

Jon_blaney · June 5

My catalytic stove was more trouble than it was worth. It required constant attendance. New stove with secondary burn is much better. A leaky old house does not need a fresh air intake.

EdTheHeaterMan · June 5

Very little experience with wood stove and the technology of pellet stove in practical use. I had one customer with an outdoor wood boiler that needed it connected to his Weil McLain WGO boiler that had Plus 40 indirect. The wood stove installation did not allow for heating the indirect and he ended up using unnecessary fuel oil for DHW. I redesigned the piping and control logic to use the wood stove water more efficiently.

Another customer had a combination oil fired / wood stove boiler in the basement. The previous owner had it installed and the current owner (my customer) never used any wood at all.

Finally, I bought a used wood stove for my family room (almost 40 years ago) when the house was still all electric. I was told that it would burn for 17 hours without needing attention, I could never get it to stay lit for more that 6 hours. That meant that it was always flamed out with no hot coals available to re-stoke the fire after a day at work or the next morning. So, the electric heaters were on when ever I woke in the morning, or returned from work. Not happy with the results.

Bob Harper · June 7

I sell stoves and have a lot of industry experience. When the Arab world attacked Israel in Oct. '73 and we were embargoed for helping them the current energy mania ensued. Every welding shop in the country fabricated steel boxes to burn wood. They gave off good heat but were creosote factories. UL came up with their 1482 listing for freestanding stoves (not inserts). We learned about controlling combustion through air control, preheating air, air washing the glass, and secondary combustion. Dan Henry, co-founder of Quadrafire(Alladdin Stove) with Alan Trusler, who had been building stoves since '76, figured out burning smoke 4 times. As we entered 1986-87, Oregon and Colorado introduced legislation regulating wood smoke. Stove pipe was reduced to 6" from 8", smaller air intakes that preheated the air and split into a secondary combustion chamber over the fire chamber. Everyone experimented with firebrick, ceramic fiber boards, ceramic fiber blankets, etc, usually lying on secondary air tubes. The chimney fires and dense smoke continued and so did the regulations as the EPA thought that looked like fun and took over. A few years later they tightened emissions again. Each step of regulation forced most of the mom& pop mfrs. out of business as prices shot up. Experiments with catalytic combustors helped scrub the smoke and get more heat out of the wood. However, early cats, (Dow Corning was big) suffered failures from improper burning, care design and materials.

Around 1977, some eggheads in Sweden corresponded with eggheads at Princeton about a new technology they developed to measure building envelope performance. The blower door gave us invaluable info. on how structures worked or did not. A new field called 'building science' arose.

The codes and standards typically ran 10-20 years behind knowledge and technology. They currently run about 8-10 yrs behind. I sit on numerous code cmtes. and can attest to the slow response. I will point out that model building codes focus on fire safety, life safety, durability, habitability, indoor air quality, and construction technology/ materials.

There are a number of stoves on the market with outdoor air capability. However, the new EPA 2020 regulations killed that for most of the current stock as cold outdoor air inhibits efficiency and emissions. They are also horribly unreliable. ASHRAE did a study of passive MakeUp Air(MUA) using a detached house. The results were that passive MUA is completely unreliable. Let's say your stove intake is located at the back of your house. The wind blows at the front side putting the MUA intake in a negative pressure zone. It will tend to pull heat, smoke and gasses backwards out of the air kit. My buddy, Dale Feb, shows a video of flames shooting out an air intake during wind gusts.

Cold air hurts combustion efficiency. You have to preheat the MUA to do any good but that hurts stove efficiency and emissions. The whole mess about using MUA instead of indoor air is hogwash. Fix the house and the stove, fireplace, water heater, boiler or furnace will usually work if the rest is proper.

Modern cats typically carry warranties ranging from 10-20 yrs btw for the first replacement. The cats help pass the EPA 2020 stds so the stoves can qualify for the current IRS 30% tax credit with a $2K cap.

HTH
.

leonz · June 8

Buy another pellet stove.

LS123 · June 8

@Bob Harper , Thank you! Information is very insightful! especially about the location of outside air intake and having it in the wrong place and consequences. I was wondering, assuming there is a outside air intake place in correct location, what percentage would the efficiency drop during really cold days ( or cold air in general) Is there any formula(s)? Where can I get more info (or anything you could point me to?) Just curious to know if its worth having outside air intake wood stove, for example if the efficiency drops 5%, 10% etc. Thank you again!

**The location of the wood stove would be in the basement.

@leonz , thanks… but I would like to have a source of heat during winter that do not need electricity (in case of extended electric outage…I do have a back up generator. I dont like the constant noise. Pellet stove, and Steam boiler need electricity) Plus pellet stove feels like forced air too… During really cold / windy winter days, indoor temp drops really fast (when the pellet stove is off for couple of hours, wood stove also feels like radiant heat). Plus there are lots of fire wood available in the area I live at ( and very affordable)

JMWHVAC · June 8

Bob Harper, thanks, you could write more pages! As a user & lover of wood stoves I like to read all there is on the subject. A big issue for clean burns that I don't seem to see much on, is how the fire is managed. I don't have to sweep my chimney even tho my woodstove is my main heat ( well, lets say at least not more than once in a handful of years). I am not even sure when I last did it. The powerful draft takes the powdery flakes out the top when it is windy and the stove door is opened for reload.

We do not do "overnight burns". (Overnight smoulders??) Ninety percent of the time that we have a fire going there is no visible smoke coming out the chimney. Typically we only add two pieces at a time and they are placed with "mating" sides so they burn from the center. When heat is needed overnight two large pieces will keep things hot for a lot of the night and normally we let the house cool down overnight anyway.

leonz · June 9

It is a case of do you really want more heat or not?

An Ashley console coal stove can do this for you without electricity, and you can use wood or coal in it, and it also has a cook top. The Ashley console coal stove has a fire brick lining to hold in more heat as well.

LS123 · June 9

Thanks @leonz. I do not need more heating in the house. Having diversified sources of heat and fuel allow me to be less dependent on just one type of fuel and possibly cost of them too…

Bob Harper · June 10

The best way to burn a woodstove is like a diesel engine- start it up and run it non-stop for all its service life. On and off wears out a stove an fails to reach the designed efficiency and emissions goals.

A basement is under the Neutral Pressure Plane and thus a negative pressure zone. Basements are the toughest locations to achieve sufficient draft pressure compared to upper levels.

LS123 · June 10

Thank you @Bob Harper!

WMno57 · June 10

Neutral Pressure Plane is a new concept for me. I had to learn more. Found this:

https://bluehouseenergy.com/blogs/bhe-blog/what-everybody-needs-to-know-about-building-science-neutral-pressure-plane

Kind of like PONPC in a hot water heat hydronic system.

thanks @Bob Harper

LS123 · June 10

@WMno57 … thank you for the link. Its very informative!

kenjohnson · June 12

I have owned and burned wood stoves for nearly 20 years that are based on secondary reburn tubes and that use catalytic converters, with and without outside air for combustion. My latest stove is a Woodstock catalytic stove that uses outside air for combustion.

If you have dry wood (dried outside for 2 or 3 years, covered, in an open area and not shaded), catalytic stoves are a dream - you load them up on a hot coal bed and 15 minutes later you can walk away from it after two or three adjustments and it just burns clean for the next 12 (or more) hours. I load mine twice a day in the winter. It's easy and its clean. Cleaning the catalytic converter is easy and is done once per heating season and once at the end and takes about 20-30 minutes total. The cataltyic converter lasts 3 (or more) years (depending on how much wood you burn per year). I wouldn't never go back to a secondary reburn tube stove.

My secondary reburn tube stove was a great stove, but it is much more finicky with adjustments to keep it from burning too hot and too fast and/or not burning hot enough and causing more smoke than I would have liked (I lived in a compact village at the time). This stove could burn wood that wasn't as dry but was more finicky to operate if you wanted to burn cleanly (some don't care about the latter - I do). BTW, clean burning means more heat for the same amount of wood, and less creosote build up, so why you would not care about clean burning is beyond my ability to understand).

There are newer stoves that are hybrids of the two approaches.

A quality stove of either type will work well, it's just a question of how clean you want the burn and how much you want to tend to it. If someone says one is better than the other for some other reason, there is usually some deeper (and unsaid) other preference they have that drives their opinion (my experience).

If someone says that wood stoves don't work well, or new stoves don't work well, or catalytic stoves don't work well for whatever reason, it is because they are either not well informed and/or they are burning wet wood. Newer tube and catalytic stoves need wood with moisture content of 18-20% which is only achieved with 2-3 years of drying outside in an open area in the wind and covered the entire time (depending on species of wood and size of splits). Old stoves didn't need such low moisture content, but then again, they were less efficient and caused more pollution.

Bob Harper · June 13

Here is one of the best treatises on atmospheric venting and pressure gradients: http://www.gulland.ca/fhs/hhstoc.htm John, working with Don Fugler at the Canadian Mortgage Home Corp. literally wrote the book on it. They conducted experiments, such as calibrating a plastic garbage bag for measuring air flow (it works). They measured air kit flows. E.g. a 4" smooth duct with one gentle broad radius 90 bend under a 5 Pascal gradient can expect about 10-14 CFM on a good day.

The Energy Conservatory made the Minneapolis Blower Door, which is the big daddy. Get the handbook. Tons of free info on pressure diagnostics. Gary Nelson is a legend. https://energyconservatory.com/support/

Another MN legend is Paul B. Stegmeir. He used to drive over to Burnsville meeting me at my hotel whenever I was in town for something at the Hearth N Home Technologies HQ in Lakeville, MN. Paul has been involved in most research, codes, stds. and testing since the 1970's. He worked with Gary Nelson on the Minn Airport noise contour research and reports. The FAA allows 65db max 24hr. avg. This zone failed so lawsuits ensued resulting in a Sound Attenuation Zone with extra tight construction. No atmospheric venting. Sweaty, stinky houses> HRVs and ERVs. Higher construction costs and taxes. The usual.

Fun stuff.

Bob

psb75 · June 17

How come no one has mentioned a masonry heater with large heated mass and convoluted flue, like a Russian stove, or German kachelofen (tile stove)? These are really efficient, low maintenance and use 1/3 of the wood that all metal wood stoves do. Tulikivi is a Finnish soapstone version of this. Oh, by the way these are not "appliances" that you can just "pop" in and out of a building! They are usually built into the building.

LS123 · June 17

@psb75 , I agree with you about the efficiency of mentioned masonry heaters.

I think in US, most people like to modify (customize) their house structures more frequently than other countries (based on my knowledge.. but may not be 100% factual.) Plus I dont know the cost of building one, space required for masonry stove.

In my case, based on cost and location where the stove would be, its preferable to have a wood burning stove.

psb75 · June 18

The cost and space for a masonry heater are considerable. And you are correct about Americans and frequent customization. I remain fascinated by this very old and near-perfect combustion technology. To your original question about outside air for combustion I believe masonry heaters can effectively use this. By the way, I forgot to mention that like other modern efficient wood-burning technology, masonry heaters demand fully seasoned, smaller-split wood. Proponents say that soft wood can work almost as well as hard wood. I also need to concede that masonry heaters don't work very well in the early fall and the late spring—as far as convenience. Woodstoves are the answer to that. Significant winter solar gain in an efficient house would also be a drawback for a house with a masonry heater.

Larry Weingarten · June 18

Hi, There is a middle ground here between high and low mass stoves. It's called a rocket mass heater. The book on it was written by Leslie Jackson: https://www.amazon.com/Rocket-Mass-Heaters-Ianto-Evans/dp/B01FIX87WG

There are a number of videos on this type of stove as well.

Yours, Larry

psb75 · June 19

Yes! I am interested in rocket mass heaters. One called "batch-box rocket mass heater." All of these are self-built. There is a gentleman named Peter van den Berg that has done much interesting work on this.

Wood Stoves with Outside Air Intake (Benefits/Disadvantages) - (Catalytic/Non-Catalytic) ?

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