Chimney height related to stove size in North Florida? Need Draft!

[Wakomon]

BeGreen raised a question about the Jotul Oslo size vs our proposed 13 ft Metal-fab chimney in my first post.

I didn't think of the relationship between stove size, chimney height, and climate (mild by comparison). So let me add more info - and raise more questions.

We are planning to get a new woodstove and chimney system (hopefully this winter if we can figure this out.)

We burn fires when temps are mid-40s and below. (Gets down to teens some nights.)
Our hearth is in a room about 320 SF with ceiling at 6:12 pitch, at 8' to 13' high... but there are two adjoining rooms with no doors, one being an upstairs room. Total SF of all three spaces, plus a bit for the top of the LR, I figure to be about 1000 SF. The whole house is 1800SF.

Here are some sketches I just did this morning to give a better idea of our set up.... both the existing stove set up and our plan.

Our local woodstove dealer (and only known local installer) sells Jotul, Lopi, and morso... though they have no wood burning stoves in their showroom. My wife and I made a trip to Gainesville recently to look at these stoves (as well as VCs, and Windsor steel stoves). We liked the Jotul best. We also researched PE Alderleas, but there are no dealers anywhere close to us.

Our old Sierra (steel) has been a real workhorse and has required little maintenance and no repair for the past 25 years. It is oversized and can heat us out of the room. But it is tough to start, and we have had to deal with too much smoke in the house. We use split oak from our own woods, seasoned at least a year. We want a stove (and chimney system) that won't smoke when we open the door to reload, and burns cleaner. (The Jotuls offer the enticing option of a screen for open fire viewing - does that really work?)

Our old stove is a side loader. The Oslo also has a side door which is appealing for reloading a hot firebox. The next size down - Castine - does not have the side door.


So, what size stove? Should we make the chimney taller? By how much? Is the Oslo too big for our house? Is Jotul a good choice for us?

All feedback will be much appreciated.

 

[oldspark]

Not sure if this is any use to you but here is an interesting article.
https://www.hearth.com/econtent/index.php/wiki/why_stoves_overfire_from_too_much_draft/

 

[Battenkiller]

No wonder you had a hard time starting and burning smoke-free just looking at the chimney setup. As far as the new chimney, you might squeak by with that short a flue height with some stoves up in the north here, but from what I read, even northern folks are happiest with at least 16' with the Oslo. Your average heating needs are equivalent to our shoulder season needs. Extra height helps in the warmer temps.

Personally, I think that stove is way overkill for your needs. We have a few northern members here who get tons of heat from the Castine. I think it would be a more appropriate size, and you will get better heating efficiency with a smaller stove (less wood used for each BTU in the room) because you will be able to run it at higher (cleaner burning) internal temps.

 

[nate379]

With your warm temp and high humidity I think taller would work out better. I don't think you will have enough draft with only a 13 chimney unless it was quite cold (below 0 temps)

I only had about 15ft and I found when it was warm out (mid 30s) that it was tough to get a fire going. It worked fine when it was down in normal winter temps, 10-15* or colder though, but it made the shoulder season almost impossible.

I added another 3ft section this summer and it made quite a difference. I have had no trouble with a fire burning well even with temps to upper 30s. (I don't usually bother to run the stove in temps warmer than that)

I can't really tell you what stove to get though give your mild temps I would consider something fairly small. I mean you could install a Blaze King, but you'd have to burn 2-3 logs at a time to keep the house temp under 80*! Even with temps at -20* and the air control all the way down I have to space out loading my stove or it will sweat everyone out of the house.

 

[spirilis]

Draft is driven by pressure & temperature differentials (temperature usually having an influence on pressure) so to compensate for warmer outside temps (=lower inside-of-flue vs. outside temperature differential) you want a taller chimney. 15-16ft minimum IMO... that link Oldspark provided talks about EPA testing against a 15ft flue. It is good that your new configuration will be a straight-shot vertical chimney.

Stove size is up to you, I kinda think for the space you're heating (1000 SF) the Oslo sounds too big. I wanna say I've also heard folks complain about the Oslo's performance with anything under 20ft flue height but I'm reaching from memory here.

edit: Here's one mentioning it... https://www.hearth.com/econtent/index.php/forums/viewthread/83643/

 

[mellow]

My take would be to keep the Sierra, for the little bit you burn an EPA stove is not going to save you a lot of wood, and if you burn it hot it will burn clean. What I would spend money on first is running an insulated liner down that chimney, I would run a 6" and extend the chimney up 2+ feet past the crown.

It is not your stove causing your problem of smoke spillage, it is your chimney.

 

[Wakomon]

Thanks to all for all your insights.
We will chew on this. (and anymore tips.)

Our concern with the old Sierra and chimney is the 2 ft horizontal run from stove to chimney, assuming it would even be possible to hook up a 6" liner, or fit the T down. (That would be great if it would work - no additional holes in the roof!) We've also considered keeping the old stove and adding the new flue for it. Still a horizontal connection, (but much shorter) and we'd have a straight-up insulated chimney from there.

I don't entirely understand the influence of the outside temps given that the flue first runs thru the warm room and then thru presumably well-insulated pipe above the roof... but more height makes a lot of sense. Not to doubt the outside temp/pressure/humidity influence, just harder to wrap my brain around.

 

[begreen]

There are a few issues here. The mild climate, the short flue and modern EPA stoves. Many modern stoves require more draft than the old air tight stoves because they work on different principals and assumptions. The old stoves were designed so that you could get the fire going good, then close them down by cutting off the air supply. This meant that you could wake up in the morning and still have hot coals. But the reason this worked was that it reduced the fire to a smolder which could (and often did) result in a tremendous amount of smoke spewing out the chimney and bad creosote buildup. Modern stoves do not completely cut off the air supply. To eliminate smoke they reburn the wood gases before they head up the flue. Some do this by introducing secondary air at the top of the firebox after preheating it via air channels built into the stove. This can be very effective, but it takes stronger draft to pull the air through those channels and out of the secondary manifolds. Thus the need for a better flue.

This article should provide some helpful guidance about the importance of flues and the influence of temperature on draft:

http://www.woodheat.org/all-about-chimneys.html

While at the dealers, look at the Morso 3610. It is a relatively easy drafting, 2 cu ft stove that might work ok here. Also, I would recommend you consider a catalytic stove. In your mild climate a cat stove is a good fit. They tend to be less fussy about draft because instead of drawing in secondary combustion air, they use a catalyst to reburn the wood gases. The other nice thing about a cat stove is that they can run at low output for hours without smoldering. This is ideal for mild climate burning.

The Woodstock stove line is very popular with Hearth.com stove owners. They don't have a showroom and only sell direct. Fortunately, their customer service and products are excellent. And they have a no questions asked return policy. If you don't like it, return it within 6 months for a full refund (less shipping). www.woodstove.com. If I lived in N. FL I would be putting in a Keystone in this house. And I would probably try it hooked up to a 7" insulated liner in the brick chimney, with a 2 ft extension on top like mellow suggested or perhaps an extendaflue - www.extendaflue.com for a nicer look.

 

[Wakomon]

Thank you so much. That article about chimneys was very helpful. We ended up just putting in the new flue, but added 4 more feet than we had planned. And now our old Sierra works like a dream. No back puffing AT ALL. Super-easy startup. Won't burn all night like it used to, but I suspect our old smoulders were not good for the stove or chimney, and it's so easy to re-start the fire in the AM that it's no biggie. We sure appreciate the help from everyone.

 

[HotCoals]

Good deal!
You have oak in Florida?
Thought there were just palm tress there..lol.

 

[begreen]

Thanks for the update. I'm glad the Sierra is working well now.