Proper flue/masonry chimney connection?
RustyNail
| Posted in Energy, Heating & Insulation on
Hi all! What is the proper means to connect a metal flue pipe (coming off a hot water heater) to a masonry chimney? The flue is standard single wall pipe (exposed in the basement), passing into the chimney.
Do I just install a standard piece of flue pipe, similar to the metal flue leading to the chimney from the water heater? I ask since the previous installer did as I just mentioned… and it has since rotted out inside the concrete block (block surrounding the terra cotta masonry flue.
Thanks in advance!
Replies
i'm confused .... if it's a masonry chimney... does it have a metal flue liner or a clay flue liner ?.. i think it has a clay flue liner from your description
ok... does it have a thimble let into the clay flue liner
sound a little jury rigged ....
other than the previous one rusting/ corroding.. you could simply do the same thing.... maybe a heavier guage
if there is a heat issue .. with the flue pipe being too close to combustibles... you may want a heat shield
It's a masonry chimney (block/brick) outer with clay flue liner.
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Nope, no thimble let into the clay flue liner for the hot water heater. Just the single wall metal flue stuffed into a hole knocked though the outer block and inner clay flue of the chimney (with mortar slathered around the metal flue).
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Looks kinda jury-rigged, but an HVAC guy I just had in for some other work said that that's standard installation. I asked "no requirement for stainless steel/clay thimble of sorts?". "Nope".
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To me, it's something that just looked so crappy, I had to ask whether this is really the way it should be done...
Otherwise... no heat issues (i.e. no fear of nearby combustibles becoming kindling)...
take a look at your clay flue liner.... if it's in good shape... then the heavy guage metal thimble / lead-in will be just fine
worked ok for the previous, right ?Mike Smith Rhode Island : Design / Build / Repair / Restore
From what I am reading, it sounds like this was added to a flue designed for something else. Is that true? Other than that - going back to the original question - the firs thing to do is to inspect the chimney to see if it is safe, and then to be sure it is the right size.Most times, the right thing to do when adding an appliance to a flue already in place is to line that flue with SS to downsize it to the right size for that appliance. Modern fuel burning appliances are more efficient so they tend to produce more condensation. They don't run long enough or waste enough heat energy to keep the flue warm, so the water vapour by product of combustion will condense in the cold flue. That water is probably the reason for your rust.
Stainless steel or heavier gauge will deal with that, but there could still be more necessary. A common mistake is to say - hook up a burner needing a 6" round exhaust to an 8" square flue. That will cause a slow draft and even more condensation. That is why a liner to re-size the flue can be needed.
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It appears that the chimney flue was used for both the hot water heater and furnace years ago. The chimney actually has three thimbles: one for the old furnace (no longer in use, due to a high-efficiency furnace now being in place), one for the hot water heater (in use, and the source of this question), and one for possibly a previous hot water heater (it is a clay thimble, but is too low and has been mortared up).
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I'm thinking you're also correct about the flue actually now being too big for just the hot water heater. I believe the clay chimney flue is 8x12...
<!----><!---->I'd put in a liner, but since this house will be going up for sale soon, I'm looking to spend as little $ as needed...
Well, I think you now know what the problem is.
8x12 is far too large for a water heater.One more problem with that - the oversized flue can make it so hard for a good draft to get going, that the fumes can gutter and spill inot the house.So get a couple good CO meters to warn you that you are poisoning the family
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"I'd put in a liner, but since this house will be going up for sale soon, I'm looking to spend as little $ as needed..."LIABILITY ALERT!If the buyer should suffer injury resulting from gases spilling into habitable spaces due to that over-size flue - the previously mentioned guttering or a corrosion failure of the water heater flue or whatever - you could have an expensive lawsuit filed against you that would make the cost of a liner look very cheap.
BruceT
I know, I know... another one of those, you touched it in some manner, now you're liable. Neglect the fact the venting has been like this for an unknown number of years (13+)...
what RE law says is that if you KNOW about a defect and fail to disclose it, you have a liability and penalties can apply on top of the liability. Not that you touched it, it is that you knew it needed some correction.
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In the effort of trying to learn something new... how do I know that I need a liner, and what size? In the IRC, for draft-hood appliances in masonry chimneys, all I see is the max allowed appliance input rating. No minimum (as the min/max applies to fan-assisted combustion systems). I know I have to be missing something, just not seeing it. <!----><!----><!---->
The water heater setup is as follows: 32K BTU water heater equipped w/ draft hood (not high efficiency heater). The connector (draft hood to chimney) is 3" single wall, 8' long (1' rise), connecting into masonry chimney flue, 8" x 12", approximately 30' long. Again, this is now the only appliance using the chimney. <!----><!---->
From looking at the code book, it appears there's also code compliance issues with the connector, in that it needs to be 4" pipe. <!----><!---->
Oh, and please don't refer me to an HVAC guy!! Been there, done that, and he saw nothing wrong with the setup. :-D Really... Just this past Wednesday. And he was by far the better of the two HVAC guys that I've used in the recent past...<!----><!---->
"how do I know that I need a liner,"'cause a bunch of yahoos on the internet just told you so
;)"and what size?"There is an install manual that came with the unit. If you don't have it, you can find it on the web in *.pdf format at the manufacturers site, or you can call their tech help line.Going generically, since you have a 3" flue feed and that is typical for that type heater, the manual probably calls for a 3" flue, so you should have nothing larger than a 4" the rest of the way out, or have a mechanical assist ( in line fan linked to run when things fire up and for a period after the flame goes off)
But if code suggests 4", that may be the main flue requirement - I am not reading it myself. Sometimes manufactures specs dominate, and sometimes codes do. for now, my interpretation would be that the manufacturers on yours says 3" and the main stack should be 4"
What size is the actual exhaust on the unit?BTW, an 8' nearly horizontal line is also contributing to your problem with draft.
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No, no... I'm not going to imply anyone here is a yahoo! :-D I appreciate the input... I learn, but know enough to go back and check things stated online...
The install manual... kinda useless. It discusses only the connector size, nothing about the vent, and not venting tables. It just refers you to the National Fuel Gas Code. This heater will probably end up getting replaced, as it's past it's expected life (installed in 1995). <!----><!----><!---->
I think I found what I was looking for after I posted last night, telling me how I know the vent's too big. It wasn't in a table, but in the following text, as it applies to masonry chimneys venting a listed appliance with draft hood/category 1 appliance (IRC 2427.5.4): "For sizing an individual chimney venting system for a single appliance with a draft hood, the effective areas of the vent connector and chimney flue shall be not less than the area of the appliance flue collar or draft hood outlet, nor greater than seven times the draft hood outlet area. <!----><!---->
And no, the text wasn't underlined for me in the book, so I'm not that blind! ;-D<!----><!---->
To answer your question, the exhaust on draft hood is 3". So, area of 3" pipe is 7.1 sq in. Area of the existing flue is 96 sq in, well over the 49 sq in max (per the above citation). <!----><!---->
The 8' line, with 3" appears to be a problem. From what I read, two different problems with it (based on IRC G2428.3.2 and 3.3):<!----><!---->
OK, you have some hard info to work from now.My experience is in solid wood appliances mostly, where a lot of other influences and variables are learned.What is not specificly covered in addition to why you have recounted here is the combination of the flue size problem and the horizontal run problem. my instinct is that a specific analysis of your installation by an expert yahoo would indicate that you'd definitely need less than a 49" flue cross section or a shorter feed line or a greater up angle or a combination of all the above.Simplest of course is to just use the 4" all the way.
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On Edit-Note: I wrote this before reading the whole thread: So consider this confirmation.
FWIW, the better heating contractors in my area automatically install a flue liner for the water heater when changing out to a 90+
Consider finding a qualified HVAC contractor in your area using the contrator locater at http://www.nationalcomfortinstitute.com
>>it has since rotted out inside the concrete block (block surrounding the terra cotta masonry flue.
OK. You've been getting condensation at that point - showing, or at least suggesting, that the block/liner is relatively coldand thus the flue gases are cooling too much causing the condensation.
I'm guessing the chimney/flue originally served both a furnace and the water heater, and now the original furnace has been replaced with a side vented 90+ furnace, leaving the chimney much cooler than before.
If so, a flue liner should be added to the water heater flue as it passes up through the chimney.
In NW Ohio, for a 2 story house, you'd be looking at $300+/- installed price.
Or you can DIY.
If the furnace hasn't been replaced, check for too much air getting into the flue (either at a flue connection or through a cleanout reducing the effective draft in the water heater (and furnace flue)
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Edited 7/6/2008 11:36 am ET by rjw
Oh yeah, if your house is 70-80+ years old, that third flue opening may well have been for an incinerator.
Remember Mary Dyer, a Christian Martyr (Thank you, Puritans) http://en.wikipedia.org/wiki/Mary_DyerMay your whole life become a response to the truth that you've always been loved, you are loved and you always will be loved" Rob Bell, Nooma, "Bullhorn"
You guessed right, both the furnace and hot water heater used to use the same chimney. The furnace installer (years ago) put in a 92 AFUE furnace and didn't bother to address the now oversized flue for just the hot water heater. <!----><!----><!---->
Yes, thinking that both a flue liner and new water heater may be in the future...
Hmm, you have me wondering about the incinerator. House was built around 1940.<!----><!---->