sizing a wood stove

Bob Harper

Get a hearth professional into your home to consult. Go to www.nficertified.org to locate one near you. A few basics:

The chimney must have a Level II inspection. This is put an end to speculation about clearances and the condition of the chimney liner. Plan on it failing, which will then require the chimney to be relined.

Liners: for solid fuel, liners must be listed to UL 1777 with the appropriate insulation for the clearance. There are NO listed liners in the US for wood that do not require insulation. The amt.and type of insulation is determined by the Level II inspection. Plan on the framing being at zero clearance which will require the maximum insulation. This will possibly mean a 6 inch round liner with the insulation will not fit. You may have to install a larger liner that has been ovalized to meet the same flow capacity. This could actually require any old terra cotta to be broken out to make room for the new liner. Don't let the mass and size of a chimney lure you into a false sense of security--most are lousy.
With a full length liner, you can sweep it yourself. Forget about those chemical logs. For one, you cannot use them with liners as the salts in them will ruin the liner and void the warranty and listing. Two, I've never seen a log inspect a chimney or mechanically brush out the creosote.
Don't oversize the stove. If it is too big, you will choke it down thereby gunking the chimney full of creosote until you have a fire. Just because liners are tested to withstand a 2100F chimney fire doesn't mean you should try it. Do you road test the air bags in your car?
You will probably need additional hearth extension protection and possibly a mantel shield--see the listing of the stove.
Good advice on ash removal-- get one of those metal cans with a tight lid and never place ashes into paper bags.
You want hardwoods seasoned to a moisture content of 12-18%. Get a moisture meter ($100) and test your wood.
By sweeping the flue yourself, you gain valuable feedback on how you are burning. If the room is too hot, reduce the fuel--not the air.
Remember, the stove doesn't have air ducts like a furnace so don't expect it to heat the entire house.

For the cleanest burning stoves on the market, check out: www.quadrafire.com

Dan_15

I’m a H.O. who reads these posts diligently and I thought I could ask your help on a sticky problem. Im trying to size a wood stove for my house. The stove will reside inside my fireplace, which is located in the living room on the first foor. I’ve done a room-by-room heat loss on the entire first floor. The nominal output of the smallest size stove is 3.5KW or about 12,000 BTU. This would plenty of output for the living room, which has a heat loss of 8800 BTU. The next size up puts out 6KW or about 20,000 BTU. I’m stuck trying to figure how the stove will affect the other rooms that are adjacent to the living room. Is the convective/radiant nature of the stove strong enough to move cold air from the adjacent rooms and deposit warm air into the adjacent rooms? I assume that the convective effect will depend on whether there are obstacles like walls and doors in the way. This is a small house—1750 sq ft—about 900 sq ft each floor. The layout is like a shoebox colonial style with typical boxy rooms. Its not exactly an open plan, but there are quite large openings connecting all the rooms on the first floor, so it seems like there is much opportunity for air to move around. I can make a straight shot from one end of the house to the other, with nothing in the way (see photo—the fireplace is next to the lounge chair). Is there any more scientific method for understanding convection in this kind of situation? Im not planning to use the stove as my sole source of heat—it will be merely supplemental at best. But if I can size the stove properly, it would be a nice bonus to rely on it for more than just supplemental heat. Thanks, Dan

Plumdog_2

I would get the larger one

You will be surprised at how the heat will migrate thruout the house. And that's a nice house, too. Get an insert that has a blower and make sure you get an expert to look over the chimney and install the insert correctly. And don't forget to clean the flue as per the installation schedule. Ah, the sweet smell of wood burning in the stove. I gave up woodburning 11 years ago but now I'm gonna do it again because the gas around here doubled in price and it will go up again.

LarryC

Wood stove heat circulation

Moving heated air is the key. Use ceiling fans if available, rotation so they suck air up under the fan and blow the warmed air down along the walls. Mount "muffin" fans along the tops of door openings to move the warm air from one room to another. If possible, force cool air from the second floor back down to the first floor. Remember the air acts alot like water, you have to have room for a chunk of air to travel up, at the same time other chunk of air has to travel down.

If the house allows it, look for place(s) where a opening in the ceiling can allow the air to flow straight up to the second floor.

LarryC

Joe_76

I have to agree with what is already been posted. I would like to add that make sure the BTU rating is with the same type of fuel you will be using. Most wood Btu ratings are with hardwood about 10% moisture content or less. The wood fired boilers I carry are rated this way, so that means with the wood we have in Montana (Pine,Fur,Larch) you see less BTU output.

Douglas Hicks

So you are going to make your fireplace into a furnace. There are potential problems you may not be aware of.Before the installation of your furnace, make sure there are not any hidden combustables inside your fire place. Many fireplaces have wood framing members hidden in the brick. I do not remember the required clearances, but most of the fireplace/insert fires I saw during my years of service as a firefighter were because of inadaquate clearances in fire places. When you put your wood stove into the fireplace, you have exceeded the design paramters of the fireplace. The fireplace is not designed to contain the amount of heat produced by the stove. The fireplace is designed to have cooling air circulated around the brick. When the air does not circulate around the brick, the heat is transferred to the wood inside of the brick. After a period of time, the wood pyrolizes. Pyrolize means the temperature point at which the wood burns is lowered. We then have a fire in a non-accessable area. http://www.starschimney.com/safety2.htm When the insert is installed, the smoke damper is to be removed, an adaptor installed in place of the damper and a pipe is run to the outlet of the insert. If the insert is not installed properly, creosote falls from the flue the the top of the insert. The next problem is when the chimney is cleaned. Not all chimney sweeps will take the time to pull the insert out of the fire place. When the insert is not pulled out, the top of the insert is covered by creosote. Creosote is flammable, and will burn. When the creosote burns, the problem of pyrolized wood is increased. Another result of burning creosote is the increase in temperature of the brick and/or the lineing of the chimney. When brick gets hot enough, it cracks. The mortor may also crack or otherwise be compromised. We then may see flame shooting out of the chimney. If the chimney was built w/o adaquate clearance, the nearby combustables may catch fire.

I do not want to scare you, but in the fire service, we always strongly advised against the installation of inserts. If you decide to procede with this project, please invest in 110V smoke alarms w/battery back-up, fire extinguihsers (and not the cheap ones with plastic valves), & more insurance. Most importantly, plan for the eventual fire and have an escape plan to get out alive.

Do search for chimney cleaning and ask the sweeps opinion on this project.

Douglas Hicks
General Fire Equipment Co of Eastern Oregon, Inc
25 years on the end of the hose

Jeff Lawrence_25

former house

The house we moved out of a couple of years ago had a wood burning insert in the fireplace that was located in the den. I could get that woodstove cooking and when I got the room up to about 75 degrees, I'd turn on the fan on my furnace. Yes the air coming out of the registers would be cool to the skin, but after a little while, the entire house would warm up.

As someone else mentioned, a ceiling fan in the room was an immense help.

hr

Most important, a top drawer CO detector!

A must when burning solid fuels, or any fuels inside the living space.

hot rod

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Dan_15

Great advice from everyone; thanks so much for your input. Ive decided to get the largest size stove which has an output of 8KW, or about 27,000 BTU. Should be very effective for heating the first floor of only 900sf. Im going to see how well the convective effect works, and I'll use strategically placed fans if necessary to move the heat around. I'm really mindful of creating a fire hazard, so I appreciate the input from a former firefighter. To calm your fears, please be assured that my fireplace (which measures 31 x 37) is carved out of a solid brick base that measures 62" x 60". The clearances to combustibles should pass MA code with plenty of room to spare. Nevertheless, Im going to ask the installer to pay close attention to clearances and look for the possibility of wood framing hidden in there. He has been rebuilding custom fireplaces in MA for a couple of decades, so I trust that he knows what is going on inside an 85 year old chimney. Im going to line the flue with a new stainless steel liner with positive connection to the stove, so the system should be totally closed with no opportunity for creosote to get trapped on the smoke shelf. Oh and I should mention that my town requires a permit to install any solid fuel appliance and a fire inspection. (Not that inspection means anything--when the fire dept inspected my new boiler installation they completely missed the lack of drip legs on the T&Ps, although they did look at the flue connections and shut off sensors). Hot Rod, you are totally right about the CO detector. I've got an NSI3000 near the upstairs bedrooms, and I was thinking of getting another for the stove. I'll have to make that a definite yes. Thanks again all. Dan

Leo

A little more input

Dan as one who has been a Call Firefighter off and on for the past 37 years make sure you keep the chimney clean and dispose of the ashes properly. These are the two main things I have seen turn a house into rubble. A liner is a good thing but don't push your luck. In cold weather make sure the basement pipes don't freeze if you are using mainly wood. The money saved on oil or gas will be off set by thawing and fixing broken pipes. In defense of the Fire
Dept they aren't inspecting the plumbing they are inspecting the oil tank and burner to be sure it meets the fire prevention codes. It is a glitch in the law.
Be careful that very warm room from the wood stove will make you so relaxed you will fall asleep.

Leo

George Peteya_2

Keep the Chimney Clean

Dan, I have been through two seasons with an insert. Chimney is lined with 6" stainless. I have found that I need to clean the chimney every 6 weeks. Much longer than that, and it gets real hard to push that brush down. Since I'm an engineer, I started putting a bag over the bottom of the liner so as to collect the accumulated creosote and weigh it. There will be many variables, including how seasoned your wood is, and how hot you run the stove. BTW, if your stove is oversized, you will be tempted to run a slow fire ... don't. In milder weather, build a hot, short term fire and let it go out. Matches are cheap. It's a shame that either the first or the second thing a stove manufacturer will tell you is how long a burn time you will get with a full load of wood.

jp_2

green wood or burn too slow

george, sounds like your wood is too green or you are shutting down your stove too much?

I burn 12 hrs everyday for about 6 winter months, have a single walled pipe all the way up and I produce zero creosote.
ash but no creosote.

after burning wood for about 6 yrs, one time I produced creosote from trying to get "all night" burns, other than that I have never had creosote problems.

Dan_15

George can I pursue that thought for a moment. Why do you think slow burns are bad? This is the stove I am thinking of getting. http://www.nestormartin.be/pdf/woodbox_technology_en.pdf

Their technology seems to be about as precise as naturally possible for a wood stove, and they claim to get 10 hour burns on hot coals if tended properly. They have an interesting remote control feature that automatically adjusts the firing rate based on indoor air temp feedback (although I have doubts about how efficient that is). I think that a stove with this design will have minimal buildup problems as long as tended properly and correctly loaded. Every chimney is different, so I wont really know until I try it. I pledge to keep a close eye on the flue before creosote becomes a problem.

George Peteya_2

Yes, at first ...

... and maybe those habits got me into cleaning the chimney every 6 weeks. I try to keep the stove hot enough to keep a Condar surface thermometer (on top of stove) at 300° or above.

We'll see how it goes this year ... about half my wood is almost 2 yrs old.

BTW - I don't try to keep a fire overnight. Too much temptation to load it up and choke it down.

I'm real skittish about chimney fires ... I had one start in a former residence, and I don't like the sound of jet engines in my house!! So I guess every 6 weeks whether I need to or not, said the engineer ;-{>

George Peteya_2

Where to Learn More

Dan -

Visit www.woodheat.org for lots of info on woodburning.

Also, Item 2 in the pdf file you referred me to (alright, the pdf file to which you referred me) mentions a shutter that is adjusted for a minimum safe burn rate. Properly adjusted, this helps protect the system from pilot error (you're the pilot).

Leo G_99

George

try to see if the Chimney Sweep logs are available in your area. They really do work, even the Fireplace Mag did a report on them and gave them the thumbs up. Last year, I used a powder that I bought from the local hardware store, same idea as the logs, but this you can pour on to a hot fire, so much more convenient. My chimney sweep was very impressed with the cleanliness of the chimney last year!

Leo G

George Peteya_2

Chimney Sweep Logs

Leo -

I googled "chimney sweep log" and came up with mostly poor reviews.

I don't mind sweeping my own chimney - it's only 14 feet (2 rods plus my arm) high, and i get a nice view of the northern Catskills from the roof.

Not to butter you up, Leo, but maybe your sweep was impreseed by the cleanliness of your chimney because you know how to burn wood and most of his other customers don't.

Bob Gagnon plumbing and heating

wood stove questions

I have a traditional wood stove vented into my fireplace with about 6' of vent pipe extending from the top of the stove up past the firebox. It is an on outside wall and its about 25' high. is this method O.K.? or should I run a liner all the way up the chimney? I'm assuming that the wood stove out in front of the fireplace I won't have the overheating issues that the inserts have? Thanks, Bob Gagnon

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Dan_15

Bob, you're in MA right. I have been told that your method is legal in MA. However, may not be efficient. It really depends on your chimney. My outside chimney is too cold and incorrectly sized to pull a decent draft. I feel safer lining with 6" round stainless steel positive connection to the stove. I'd be worried about long slow burns in an unlined outside chimney. Call this guy and ask him to take a look. Ive been impressed with his knowledge as a tradesman; he is also opening a fireplace/stove retail store first week of Sept. I thought his price to line a chimney was pretty reasonable.


http://www.erikanthonycustomfireplaces.com/index.html

George Peteya_2

I think you know the answer ...

... or you wouldn't have mentioned the 25' high, cold chimney into which you'll be condensing all that creosote!!

Run a liner all the way to the top, IMHO.

George Peteya_2

More Info from woodheat.org

www.woodheat.org/chimneys/chimneys.htm

Bob Gagnon plumbing and heating

the draft has been good for

2 years now. Pretty good anyway, I have to start it with a torch. The draft just started to slow down at the end of the last heating season. a visual check down from the top with a flashlight shows no buildup at all. I'm thinking the end of the 6'vent might have buildup? I build a big fire before I go to bed and turn the stove 1/2 way down and it seems to burn O.K. Is that way correct? It seems if I keep the fire going and the chimney warm, the draft is fine. thanks for your help, Bob Gagnon

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CC.Rob

similar setup

I have about the same setup -- wood stove set out from the fireplace a bit, 6" stainless liner goes up about 6' into a ~25 ft exterior chimney. Located 75 mi SSE of you, similar climate.

We are fortunate to have a really good chimney guy who cleans and inspects it every year. We burn only good seasoned hardwood and fire it by the book. He is impressed with how clean the system is compared to others he services. Part of this is probably due to the stove -- it has a catalytic combustion system that I inspect and maintain. Very thorough and efficient combustion. I hadn't seen that woodheat.org link before but on quick glance it looks like some excellent info.

Only under rather infrequent atmospheric conditions (prolonged periods of very cold, still air that result in poor mixing and allow temperature stratification in the chimney) does the chimney draft poorly, and then only for a minute or so at start-up. Typically if we haven't used it for several days.

I generally don't build a 'big' fire before going to bed, but tuned properly I can keep 2-3 typically-sized split logs going pretty much through the night so there's a bit left to stoke in the early AM. It's a pretty high-mass chimney and will retain warmth for over 24 hr after burning ceases.

George Peteya_2

I once had a chimney ...

... that needed to be started with a torch, too. It was an exterior Security chimney that I had had installed with extra long standoffs so it would clear the soffit, to prevent any chimney fire from spreading to the attic (see earlier post about jet engine). The whole chimney was way out there in the cold. Establishing a draft was so difficult that when I sold the house, I left a whole page of instructions for the new owner (open basement window, close door to upstairs, prop vent damper open, go make coffee, drink coffee, come back downstairs and stick torch into flue through vent damper etc. etc.). I eventually switched to coal so I wouldn't have to go through this procedure too often.

Your draft problem at the end of the heating season may be due to warmer weather (less draft then), more frequent startups, or as you said, blockage in the 6' pipe. You may also have a pile of loose creosote where the stove connects to the pipe, especially if it's a vertical connection.

Hope this helps ... and that others start to weigh in with their experience. Most of my expertise is in the area of how not to do stuff.

George Peteya_2

Amen ...

> Get a hearth professional into your home to

> consult. Go to www.nficertified.org to locate one

> near you. A few basics:

>

> The chimney must have

> a Level II inspection. This is put an end to

> speculation about clearances and the condition of

> the chimney liner. Plan on it failing, which will

> then require the chimney to be

> relined.

>

> Liners: for solid fuel, liners must

> be listed to UL 1777 with the appropriate

> insulation for the clearance. There are NO listed

> liners in the US for wood that do not require

> insulation. The amt.and type of insulation is

> determined by the Level II inspection. Plan on

> the framing being at zero clearance which will

> require the maximum insulation. This will

> possibly mean a 6 inch round liner with the

> insulation will not fit. You may have to install

> a larger liner that has been ovalized to meet the

> same flow capacity. This could actually require

> any old terra cotta to be broken out to make room

> for the new liner. Don't let the mass and size of

> a chimney lure you into a false sense of

> security--most are lousy. With a full length

> liner, you can sweep it yourself. Forget about

> those chemical logs. For one, you cannot use them

> with liners as the salts in them will ruin the

> liner and void the warranty and listing. Two,

> I've never seen a log inspect a chimney or

> mechanically brush out the creosote. Don't

> oversize the stove. If it is too big, you will

> choke it down thereby gunking the chimney full of

> creosote until you have a fire. Just because

> liners are tested to withstand a 2100F chimney

> fire doesn't mean you should try it. Do you road

> test the air bags in your car? You will probably

> need additional hearth extension protection and

> possibly a mantel shield--see the listing of the

> stove. Good advice on ash removal-- get one of

> those metal cans with a tight lid and never place

> ashes into paper bags. You want hardwoods

> seasoned to a moisture content of 12-18%. Get a

> moisture meter ($100) and test your wood. By

> sweeping the flue yourself, you gain valuable

> feedback on how you are burning. If the room is

> too hot, reduce the fuel--not the air.

> Remember, the stove doesn't have air ducts like a

> furnace so don't expect it to heat the entire

> house.

>

> For the cleanest burning stoves on the

> market, check out: www.quadrafire.com

George Peteya_2

Amen ...

... amen, amen, amen.