Venting gas wh into the chimney(is it safe?)

[Vikram Desikan]

I had my water heater replaced yesterday and one change that was done by the plumber was to vent the wh into another part of the chimney. If I'm not mistaken, there are 2 sections to the chimney. One for wood burning fireplaces (2) one for the the old boiler oil that was eventually replaced by the gas wh that was replaced yesterday.

My questions are-
1. Is it ok to vent the gas wh into the chimney which was/may be used to burn wood?
2. If ok, then what prevents the wh from venting out through my living room fireplace(located above)?
3. I live in new England where weather can be cold in Winters; should I be worried about the size of the chimney being an issue and cause backdrafts?
4. Should I call for a chimney inspection; will they be able to point out issues related to venting?

 

[Stuff]

Call a chimney sweep. Get what you have cleaned and then have them evaluate. Standard water heaters generally need a flue liner installed.

 

[Sponsor]

 

[Dana]

The situation you have is commonly referred to as an "orphaned water heater". (google it for more)

The answer to #1 is "NO!", unless the large-ish flue for the wood burners is being used regularly (as in "daily") as a space heating appliance during the heating season the flue won't be warm enough to generate sufficient draft on the low, intermittent burner output of a typical standalone water heater. A right-sized flue liner for the water heater (either 3" or 4" in diameter) could be installed in the flue formerly used by the oil burner, which is what a responsible installer WOULD have done.

The flue liner isn't cheap, which is probably why they hacked the other "solution". If the oil boiler was being replace by a gas boiler, the water heater money would have been better spent on an "indirect" fired water heater tank operated as a zone off the gas boiler, which would result in higher net efficiency overall, and usually better hot water service. That too would have probably been recommended in lieu of a mis-vented standalone atmospheric drafted water heater by a competent responsible installer.

Alternatively, a condensing power vented gas water heater could have been side vented, or with plastic venting using the now abandoned flue as the vent chase.

So, to help figure out what's the best thing to do now, what replaced the boiler?

 

[Sylvan]

When I convert heating boilers from oil to gas I call in a chimney sweep to do the cleaning and inspection and issue a certificate

If the existing chimney is defective then relining is needed

I would never connect a natural gas flue into a wood burning chimney

 

[Dana]

When I convert heating boilers from oil to gas I call in a chimney sweep to do the cleaning and inspection and issue a certificate

If the existing chimney is defective then relining is needed

I would never connect a natural gas flue into a wood burning chimney

In many (most?) locations that would even be a code violation, but I believe it can be done legally in Vikram's 02476 ZIP code ( MA), or at least may have been at one time. I've encountered it multiple times- they probably weren't all bootlegged hacks (but maybe they were?) The installer in this case apparently thought it was allowed, but I'd have to look it up.

There are lots of pre-existing kludges out there in this state. A guy I work with just bought a house in MA that came with an oil burning hot air furnace sharing a flue with a completely separate wood burning hot air furnace, where the oil burner was effectively controlled as the second-stage backup for the wood burner with some cobbled together controls. (He's getting rid of all of it before next winter, replacing it with a right-sized heat pump solution, using the flue for a wood stove for both ambience and as "Hail Mary" auxiliary heat for when the grid goes down in a winter nor'easter.)

It's a dubious practice at best, even when the wood burner is a primary space heating appliance, due to the enhanced chimney fire potential. Under NFPA 211 chapter 9 sharing a wood burner's flue with any other appliance (even another wood burner) is expressly disallowed, but there are many state exceptions. According to this reference NH allows it, but only if it's a combi-fuel appliance designed to use both biomass and some liquid or gas fuel ( not the kludge my co-worker just bought.)

There isn't much point to cleaning & relining a flue that isn't going to be used. Any clay lined flue previously used by an oil burner would be way oversized for an atmospheric drafted 35-50KBTU/hr gas water heater burner, and would need a narrowing 3" or 4" liner even if the original flue were in perfect shape.

 

[Cacher_Chick]

For am orphaned water eater it is a pretty common practice to pull a stainless steel liner through the flue to "right-size" the flue and to protect the masonry from being damaged by the natural gas by-products.

 

[Dana]

For am orphaned water eater it is a pretty common practice to pull a stainless steel liner through the flue to "right-size" the flue and to protect the masonry from being damaged by the natural gas by-products.

For a non-condensing gas water heater it need not be stainless. Most installers in my (and Vikram's) area use comparatively inexpensive (~$75 - $150 ) aluminum alloy flex liner kits (complete with trimmable sheet metal chimney top caps), and they work just fine.

It's rather pathetic , first that this is a brand new but orphaned water heater, and second that the installer didn't do the right thing and install a liner, instead opting for the questionable at best (and possibly no longer legal) hooking it up to a combined flue used by a fireplace (or two.)

 

[Master Plumber Mark]

For a non-condensing gas water heater it need not be stainless. Most installers in my (and Vikram's) area use comparatively inexpensive (~$75 - $150 ) aluminum alloy flex liner kits (complete with trimmable sheet metal chimney top caps), and they work just fine.

It's rather pathetic , first that this is a brand new but orphaned water heater, and second that the installer didn't do the right thing and install a liner, instead opting for the questionable at best (and possibly no longer legal) hooking it up to a combined flue used by a fireplace (or two.)

Its a pretty common thing and its not pathetic.... the plumber should have mentioned the option
of getting someone to install one if you wanted to spend the extra money.....most people dont
want to fool with it because it was working fine when the heater finally failed.....

We have to do this all the time and its technically not the plumbers responsibility to install a liner...
Usually its never a problem, we install the heater and tell home owner he has the
option to either have one installed by a HVAC or chimmney guy or simply live with it.......
It is never included in the heater install price....

In my own home I have a 75 gallon gas going alone up a 6x12 tile chimney that was for both the
heater and furnace... the furnace is pvc now going out the side of the house... It has worked
perfectly since 2005

they also claim it will cause moisture in the liner and eventually rot out the cement
but that could take forever to happen too.......

If you have good draw up the flu , I would not worry about it too much
If it bothers you then get someone to throw a liner down the chimney but it will cost you

I dont plan on ever installing a liner... it drafts just fine and probably always will......

 

[Stuff]

You won't see the problem as much with a high BTU burner. A friend of mine is living with an orphaned system. Issue pops up on the colder winter days as has a low BTU tank. The top of the tank has the rubber/plastic melted from the backdraft. The CO detector goes off sometimes.

 

[Dana]

You won't see the problem as much with a high BTU burner. A friend of mine is living with an orphaned system. Issue pops up on the colder winter days as has a low BTU tank. The top of the tank has the rubber/plastic melted from the backdraft. The CO detector goes off sometimes.

It must be your friend's imagination- Mark sez that almost never happens in real life. Must be just another hoax being spread on the internet by greedy liner manufacturers.

A lot of things can affect the amount of draw to expect with an oversized flue. The relative air tightness of the house, whether the flue is on an exterior chimney vs. running up through the middle of the house where it's much warmer, the total flue height from the port to the top, air-leakage into the flue from imperfectly seal other ports, the total duty cycle & BTU rating of the water heater, etc. If your friend has clear evidence of backdraft it's well worth installing a liner.

It is the installer's responsibility to install a liner if it's needed for safe operation of the equipment. The installations instructions spell out the venting requirements, and responsibility for any variance from the manufacturers instructions fall on the installer.