Flue Size??

[strmh]

Foundation is poured and about to begin framing a shop with boiler room.

EKO 60 is ordered to heat house and shop.

Tried downloading the EKO manual to figure out optimal chimney size........couldn't read the small print, and I probably wouldn't have understood it anyway.

I'm planning on a masonary chimney with conventional flue. Chimney will be inside and about 26' tall.

Initially I was going to go with an 8" x 12" flue.......I thought the bigger the flue, the better the draft, but after reading some posts it sounds like the flue can be too big.

Would I be better with an 8"x8"??

Looking for some suggestions.......thanks!!

 

[Eric Johnson]

The recommended flue is 8" round. Masonry is fine, but I'm not sure if an 8x8 tile liner is the same as an 8" round one. If so, that's the way I'd go. Insulate it good, in any event.

 

[buderus]

Hi I am new to any forum and not fluent in print, so please bear with me and keep in mind I profess to be an expert at nothing, the manual for the eko 60 calls for an 8" flue so 8"x8" will be fine. I would like to warn you away from a conventional masonry chimney. I have been a building inspector for 20 years and have seen very pour longevity with standard block chimney's with tile liners. I would recommend either an insulated metal chimney or if you want masonry, check out isokern, this is a system made of volcanic ash and has a zero clearance rating, the tiles for the liner actually overlap to make a far superior joint and are octagonal inside. I don't see chimney fires as a big concern with the eko but any advantage you can get is a bonus, zero clearance is a big bonus. I also want you to take into account your climate, the portion of this chimney that is exposed to the weather will be subject to huge temperature changes you want the most stable product available. I am not sure if cost is a big concern but insulated stainless is probably the most cost effective solution easy to clean and install for diy's.

 

[Eric Johnson]

Welcome to the Boiler Room, buderus. Nice to have the benefit of your experience and (yes) expertise.

Clay tile is far from optimum, but it meets current code and is probably the cheapest option. I have an 8" Duratech ss chimney, and was impressed at how easy it was to install and maintain. No creosote with a gasifier like an EKO, but with exhaust temps as low as you see with gasifiers, it's a good idea to have good insulation to avoid condensation in the stack. Ironic that a system primarily designed to protect you from high temps also does the job on the other end of the spectrum. Like a thermos, I guess.

Reminds me of a joke:

Lunch break in the coal mine
Wally: Otto, did you know that a thermos will keep hot things hot and cold things cold?
Otto: Ack no! [pause] How does it know which is which?

 

[strmh]

OK....thanks.....8 x 8 it is.

Never heard of the Isokern product, but I went to their site and it looks like a straight forward assembly. I'll have to look into the cost......trying my best to budget this project, but nonetheless, i want it to be right.

 

[strmh]

Eric....

This could be a dumb question, but when you say insulate the chimney....?? Between the flue and block???

 

[buderus]

thanks for the welcome eric................ Is condensation a big issue with a gasifier? if so how much? If so then a stainless stack really should be your best option both for insulation and resistance to corrosion. The amount of stack exposed to exterior would also become a big issue, is your stack interior, does condensation collect at base I have a conventional wood boiler am waiting for a gasifier and would value all your input especially since I give many people advice daily. By the way this forum is a wonderfull source of knowledge I pass it on every day to someone new to wood burning.

 

[Eric Johnson]

Around the block inside the building. You could build a chase and insulate it for the external run, but if it's short, not much point.

 

[pybyr]

OK, I'm no chimney mason, but I designed my own triple flue chimney and tended and brought mortar mix for the experienced mason who built my chimney in '99 to replace the sadly burned-out and blown-out chimney that someone built here in the 1950s--

1) it's pretty well accepted in the realm of physics, although less widely recognized in the masonry trades, that round flue tiles will flow flue gas better than the more normal rectangular ones. no corners for the velocity and heat of the escaping gasses to get lost and slow down in. round terracotta modular tiles are definitely a "stock" non-high-tech item, although you WILL have to insistently ask for them when the counter guys at the supply place give you the "duh, don't you mean 8" square" blank look

2) one thing the experienced chimney mason who built my chimney (who was also a physics teacher in his day job) taught me is that with modern tile-lined chimneys, you have an outer structure (brick or chimney block) and an inner structure (tile). And other than at the top and bottom, they are largely and surprisingly totally separate and distinct in both thermal and structural functions. The outer structure serves mostly to hold the whole thing up. The inner structure of the flue tiles serves mostly to convey the hot exhaust gas, get up to temperature fast (and keep that temperature). As I helped build the thing under the "tutelage" of this much more experienced fellow, I was in total disbelief how little mortar or anything else filled the gaps between the inner tiles and the outer masonry- the inner interstitial structure between the inner tiles and surrounding masonry seemed downright dinky ( a broken brick here, a blob of mortar there, and it looked like a sneeze would break it all apart). I kept wanting to make it a TOTAL solid mass of mortar (given my innate tendency that overkill = just enough) but he pointed out to me that it is important to allow a void between the outer and inner masses so that the flue tile can heat up fast and expand and contract independently of the outer supporting mass. 9 years later, the chimney still has a strong draft to beat the band, and has built up virtually NO creosote or other crud, nor has it needed cleaning, even once! (with old very non-airtight heating appliances so far)

 

[pybyr]

PS- DON'T go with an over-sized flue, especially for a gasifier. basic physics means that if you send something meant for an 8" round flue into a much bigger rectangular flue, it will slow down, and build up crud and condensation, which will be bad for everything and everyone concerned. gasifiers have even less residual heat in the flue gas (than old time wood appliances) to help the flue gas rise through and out of the chimney, and oversized flues have caused a lot of trouble with "1970s" semi-airtight wood stoves (like in the 1950s chimney of my house) , so don't repeat others' problems.

If your only unit will be the EKO, a stainless fabricated flue may well be the best way to go; if you really, truly, want a masonry chimney, go round-flue-tile and make it no bigger than you need for the appliance you anticipate feeding into it.

 

[strmh]

If I go with a stainless system (like Dura Tech) does the entire chimney need to be insulated? I thought it would be better to run the chimney on the inside of the building........is outside better?

 

[Eric Johnson]

If I go with a stainless system (like Dura Tech) does the entire chimney need to be insulated? I thought it would be better to run the chimney on the inside of the building........is outside better?

Like PooK says, inside is much better. Chimney "systems" like Duratech are well insulated at the factory. There's a layer of spun glass insulation between the inner (stainless) pipe and the outer (usually stainless, but sometimes galvanized) shell. You just lock the sections together, poke it through a hole in the roof, and you're in business.

On the question of condensation, yes, it is a concern. A properly operating gasification boiler will generate temps at the exhaust port of (usually) less than 400 degrees--sometimes closer to 250. There's not much margin for error with temps that low.

Since gasifiers produce gas temps below the nozzle of more than 2,000 degrees, winding up with 300 degrees after it goes through 4 feet of heat exchanger tubes tells you exactly how much heat is being transferred into the water jacket. Pretty darn efficient, compared to a non-gasification boiler.

I don't know if you can get round ceramic flue tiles anymore. I don't think so, despite the fact that they are superior.

 

[strmh]

The whole efficiency thing just gives me a warm fuzzy.....

You mention galvanized chimney.......I see that galvanized piping is cheaper, am I compromising anything by using the galv pipe?

 

[Eric Johnson]

Depends on the application, though it may be more a question of aesthetics than anything else. My 8" Duratech chimney is all galvanized except the top section which is visible from outside. It's stainless. As long as it's an inside run, I think galv is the way to go. There's a lot of old triple-liner galvanized connected to old fireplaces, and aside from being ugly, it's hanging in there--I'm guessing for the past 30 or 40 years. People even paint it, presumably with stove paint. Looks fine.

I bought it because it was cheaper.

 

[canyon]

I'd have to advise avoiding galvanized for hot gas exposure as the nasties come off at pretty low temps. The fumes are toxic.