Chimney Dillemma

Constantin

...and the question is how to best go about it. There are going to be three flues, two for fireplaces, the third for the oil boiler. While we studied DV oil boiler options, it's probably best to use the chimney instead (close quarters, some cranky neighbors and all that).

My present plan is a tiled chimey with a insulated liner for the exhaust gases from the boiler. That should minimize condensation, but it probably would not eliminate it altogether. Thus my question...

Most chimney installations I have seen use a sideways "T" to bring the boiler flue into the chimney flue, even when only the boiler is attached. Presumably, below the "T" there is a small pan to capture delicious (albeit non-edible) bits of carbon black and other nutriciously acidic byproducts of oil combustion.

Can one drain away any condensate from said pan (if it exists) or is it better to simply increase the stack/flue temperature to the point where the combination of good insulation and stack temp prevent condensation for the most part?

Do condensing boilers rely on drainback, and if so, doesn't this require the use of a 90° elbow at the base of the chimney?

Your delightfully ignorant engineer home owner....

techheat_2

Thats why condensing boilers are direct vent.Proper sizing and installation of the liner should prevent condensation with almost all situations. The only time I've ever seen condensation in a lined outside chimney was a 6 section Weil-McLain Gold underfired at .75 GPH,stack temp was 280 net.

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DaveC

I think the \"Tee\" you are referring to...

on the flue pipe is for the barometric damper. It should be in-line with the horizontal portion of the pipe, facing sideways (not down), and close to the chimney connection point. I've eaten alot of soot, doing chimney/boiler cleaning, and found none of it delicious or nutricious. In a typical tile lined chimney, the liner extends straight down (about 1 or 2 feet) to a cleanout door. This is where the condensation (and flakes of your tile, if bad enough) run down to - sometimes you see the stains running down the wall, to the floor.

BillW@honeywell

Here's a good resource...

Chimney Safety Institute of America (CSIA).They are the chimney pros, offer training and certification courses for professional sweeps, and have lots of good info. Go to the following website: www.csia.org They are based in Indiana, and have a referral service for CSIA Certified Sweeps. All the certified guys carry a picture ID with an ID number on it. Be careful of those who do not.

Constantin

Thanks Jim!

Naturally, I didn't mean for folks to eat the soot inside a chimney. I was merely trying to be funny.

Anyway, I take it from your comments that having anything other than the odd bit of soot flowing down in a chimney to be a problem. Thus, I won't worry about drainage.

As for the stainless liner with a "T", the graphic I saw showed it inside the chimney. That is, the two arms were pointing up and down, with the long end sticking out horizontally and attached to the boiler. The lower arm terminated at a cleanout. Hence my question regarding the cleanout and drainage, particularly if a condensing boiler is ever in the cards.

Unknown

Condensing boilers

Condensing oil boilers cannot be vented into a masonry chimney, period.

If your flue gasses DO condense within your chimney, your chimney will eventually wind up as a pile of rubble in the basement.

The taller the chimney, the cooler the flue gasses exit at the top. Let it condense before it exits, and our good old American High sulphur fuel will make sulphuric acid, liquid form, on the walls of your tile, inside chimney or not.

An inside chimney is much more likely to retain it's temperature between cycles, and not condense after it warms up..

Condensing is out of the question with a masonry chimney.

Noel

Constantin

Yup!

Thanks for the reply, Noel. The plan was never to fire a condensing boiler into a unlined chimney. Our current equipment choices are waffling between a oil-fired G115 or the Vitola, as the FCX series probably would have required 2 units to satisfy heat demands and could produce some interesting results WRT to the very high sulfur allowances in US heating fuel.

Coming back to the chimney, our plan (at present) is to use a insulated metal liner inside a clay tile flue. Given the height of our chimney (about 45' from basement floor to tip) that seemed like the best option to minimize condensation even with a non-condensing boiler.

While the previous 2.5"-thick brick unlined chimney system lasted about 130 years (as best as I can tell) it had enough cracks to make me wonder why/if none of the previous occupants was suffering from CO issues. Perhaps the draftiness of the house helped....

Anyway, I'm still looking for liner recommendations. The Ventinox stuff looked pretty good... Furthermore, if we ever switch to gas it may be much simpler to switch to a DV system. For one, condensing gas units aren't that dangerous WRT to siding and the sulfur content of city gas seems low enough not to cause too much objection on the part of neighbors.

Constantin

Thanks for the site!

I had a look there as well as over in the woodheat and hearth org sites. Plenty of good info there. I guess we'll go with 3x 10"x10" clay tile flues, then drop insulated liners down them. That should allow wood fires and the boiler to do their business...

Constantin

Ventinox HiFlex vs. VG vs. vs. VFT vs. FasNSeal

Has anyone had any experience with this line of SS flue liners?

• HiFlex seems to be the product of choice for wood-burning fires (warranteed even after a chimney fire). It's made of 321 type stainless.
• VG seems to be best for a condensing gas appliance. Would this Al29-4C stainless work well with a non-condensing oil boiler as well? Probably overkill?
• VFT seems to be the liner of choice for non-condensing oil appliances, even if the liner is made of the same alloy as the heat exchanger inside the Vitodens (316-Ti)
• FasNSeal seems like a pretty nifty product considering its smooth walls and Al29-4C alloy.

Any thoughts? What other brands/systems have you had good success with?

Dale

2 choices

You seem to be talking about a class A chimney with multiple tile flues. These are able to burn liquid or solid fuel and were the standard for ever. Just get a design book for class A wood, size to oil and go. You could also put in a chase and build a metal type L flue rated for oil. If you want solid fuel rated flues also you might be cheaper going with all flues tile rather that a metal class A. You need to speak with a chimney specialist to compare choices knowledgeably.

Jack_21

chimneys

With todays apppliances, masonry chimneys are great architectural devices but poor mechanical devices. Especially for oil and gas. If it was mine I'd avoid the masonry. If you want the look just frame up the top and use a brick facing above the roof on your factory built chimney system (don't use 430 ss). If you go masonry, I would install the SS liner as the flue goes up. That way you can use heavier gauge ridgid pipe sections and assemble as you go rather than using flex. Plan for quite a bit of expansion, of course. Flex is great for a re-line but why have the corrugations to catch by products of combustion, etc. AL 29-4C was originally developed for cooling water systems for nukes. Great stuff but way pricey. Impervious to acidic condensate. I think for solid fuel and oil your 316L is fine. I sold miles of it with Metalbestos and the 316 was bulletproof. The 430 end caps though.... Also I'd check Z-Flex as a manuf of these products.

Weezbo

Hello... like to offer an idea...

You know by now that i am not into code as the last word,from my experience my recommendation is to use a seperate flue for the Boiler.
It might seem too high a standard however,Such has been my experience.
I consider you a friend and wouldnt suggest you waste a Dime..
now here is a what if..WI you had a chance to get a nice buderas and what if you had a really low stack temp?
the stainless l type vent is easier to maintain and deal with. no co leaks for you constantine.

H. Green

Choices for Oil Fired Equipment

Our current recommendation for oil fired equipment is type 316 stainless. This alloy has better sulpher resistance than any of the others you mentioned. The supplier of AL29-4C suggests we not recommend that alloy for use in oil fired installations.

This link is to our customer's site which offers many choices of chimney lining systems. Flexible (corrugated or wrapped) or rigid (smooth wall for less resistance and suitable for a new construction chimney).

http://www.homesaver.com/asp/chimney_pro_search.asp#

As a side note. Whatever system you ultimately install for your oil fired boiler will probably need to be replaced when you replace that equipment. You should always size the liner after you have selected the appliance so you can optimize the venting conditions. This is particularly critical with situations where you expect some condensation in the flue.

As for your first question about the tee at the base of a reline. Many state codes require this, even though it is generally a bad idea with higher efficiency appliances. The other reason it is commonly used is that a tee can be, and usually is, supplied with a removable take-off to facilitate dropping the liner into an existing chimney without opening a large area for the chimney connector. For a newly constructed masonry chimney, I recommend an elbow at the base.

H. Green

Heat-fab

www.heat-fab.com

DaveC

Constantin, Heat-Fab is a great product...

and the people there are great too! If you're still following this post, Harold - are you recommending a condensate drain (with a loop) further down on the flue pipe, close to the boiler connection, if an elbow is used at the bottom of the chimney?

H. Green

Drain on oil fired system

Jim, possibly yes.

There is an arguement to leave off the cap and install a drain, flushing any accumulation with each rain-storm.

Even with a cap it depends on how cool the stack is and how much you expect to condense in the flue, given that virtually all systems display some condensation before reaching atmosphere for some part of each cycle.

I know you don't want to have a lot of condensate washing back into your systems.

Harold

Constantin

Thanks Weezbo!

I appreciate your note. I have been planning separate flues for all appliances as a matter of course, code or not. It's simple enough to do when you're building a brand new chimney system... As a consequence, we'll have 3 flues in the main chimney, 2 for 2 fireplaces, one for the boiler.

Judging from what I read here and elsewhere, it is probably overkill to line properly-sized tile-flue-lined chimney's with stainless exhaust trunks. We are currently considering the bellfires BMR line of fireplaces, which are happy with either 7" or 8" flues. Considering how little we expect to use the fireplaces, simple clay liners are probably good enough. Besides, between the chimney cap and the hot temperatures of the fire below, condensation should not be an issue. On the other hand, if installing insulated SS liners gets us zero clearance approval, that may change things yet again... uninterrupted up-down chases are very precious indeed!

The boiler on the other hand requires either a 5" or a 6" flue depending on what unit we end up with. That is smaller than the round flue liners used for the two fireplaces. Considering that the boiler will be used a lot more (and may condense), it probably makes more sense to line that chimney with a tile flue (7" to match the other two), then install a insulated 6" or 5" stainless liner inside. That way, two barriers exist to keep CO out of the house and condensation will only damage a easily-replaced liner, not the tile.

Constantin

Thanks Harold!

I appreciate your comments and will add your line of chimney liners to our list. It's probably best not to contemplate condensation washing down... see my comments to Weezbo below, insulation and the higher stack temps of non-condensing furnaces should be OK for us.

I'm still considering lining even the wooden fireplaces with insulated stainless liners inside a clay tile system if that gains us zero clearance approval. This is something I'll have to verify with the local inspector first (MA seems very picky in all things approval, which is OK as long as you figure out the rules in advance).

While the rest of you may be scratching your collective heads here (2" clearance to combustibles isn't that bad, right?), the house is a Victorian, with precious little room to run infrastructure. Thus, the chases next to the fireplaces would be ideal for AC ducts, hydronics lines, and anything else going to the top of the structure. The more room we gain there, the better off we'll be.

DaveC

I would promote using...

a stainless steel cap with screened protection against critter invasion on each of the flues (figure out the spacing between each flue so the caps all fit without interference) or a single (custom made, perhaps) cap to cover all three flues.

Constantin

Thanks Jim!

Yup, that was my thought too. I happen to like two products I saw over at HomeSaver, the Locktop and the Gelco covers. I would strive to keep all three flues under one cover.

In the small attached sketch, I show a top-view of the area inside the masonry brick exterior of the chimney, along with the square shapes mandated by the Locktop. The two upper flues are for the fireplaces, the lower one is for the boiler. With this layout, there is no interference between the spider legs of the lock-tops... However, I'm sure a chimney professional is likely to recommend something better that I hadn't thought of...

The below sketch is simply of interest because it allows us to use the exact same exterior dimensions of the former chimney. We could widen it, I suppose.