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 Posted: Mon Jul 15th, 2019 05:46 pm
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rhw
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Just had a brand new water heater installed replacing the one I had for 17 years. Installer upgraded the vent to the chimney from 3" to 4". Installer also mentioned that a chimney liner is needed. I have lived in the house for 30+ years with carbon monoxide detectors and never had a problem. To line the chimney will cost over $3500 as it will need to be enlarged to fit the liner. Not sure why so expensive or if there is another less expensive way to get this done. Any suggestions welcomed.

PS: We need to get a certificate from an installer that we need to bring to our town.

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 Posted: Mon Jul 15th, 2019 06:09 pm
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elenano
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My friend Larry Weingarten who probably has a more complete answer is traveling right now, so I'll do the best I can. My first question is why the installer would change from 3-inch to 4-inch. My understanding is that the vent size is dictated by the flue size of the heater. If the new heater has a larger diameter flue, then it makes sense. Back when I did inspections, I commonly saw mismatched vents and flues and sometimes it was a problem.

Second, are you saying it vents into the chimney and stops? Couldn't the vent run all the way up the chimney to the roof? That would be cheaper than lining the chimney. Larry should be back online fairly soon...
Randy Schuyler

Last edited on Mon Jul 15th, 2019 06:11 pm by elenano

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 Posted: Mon Jul 15th, 2019 06:55 pm
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rhw
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Thanks. 4" seems to be code in our area. And yes the flue from the H/W heater runs into the chimney and stops. I do no know why the vent cannot run up the chimney to the roof but I will ask. I will also wait to hear from your friend as well.

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 Posted: Mon Jul 15th, 2019 08:27 pm
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eleent
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Hello, I follow what the manufacturer makes.  If the outlet from the heater is three inch, stick with that all the way.  What the manufacturer calls for nearly always trumps local inspectors. If you up-size the vent too much, it loses it's ability to vent properly. I've seen three inch pipe run into 12 inch pipe and it simply doesn't work. That's not much different than running into a brick chimney (which will be hurt by condensing, acidic flue gasses). If there is any way to switch out your new heater with another, I'd consider going with a direct vent heater.  That would sidestep all the problems and help keep the indoor air a bit cleaner. Better yet would be to consider going with a heat pump unit if it can be put someplace where noise wouldn't be a bother. Additionally, there may be incentives to go with the heat pump. I know I've wandered a bit from the question, but it's not bad to know your options.
Yours,  Larry

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