Furnace and Hot Water Heater B Vent

Old 05-18-18, 10:01 AM
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Lightbulb Furnace and Hot Water Heater B Vent

I have an original gas furnace that will need to be replaced, and we're going to get AC installed as well at the same time. I had an HVAC person who does side work, come take a look at my furnace setup. I have a B style venting that goes up through the garage (encased in drywall and some kind of insulator in the wall) to a 4 foot tall stack on top of the garage (I have a colonial). There's a Y pipe in the basement that the original 88 carrier furnace and a 2014 water heater connect to. When the previous owners replaced the gas water heater, they used the original 3" piping, instead of 4" that's required.

My concerns are these.

I live in Rochester, NY and the winters are cold most of the time. It looks like the water heater has had some blowback at some time (Plastic is a little melted and a little singed insulation). The guy that came and is giving me a quote said that it's most likely due to the undersizing of the pipe for the hot water heater. I agreed but want advice on this.

Will I need to get a new power water heater because the heater will now be orphaned if I decide to get an 90+ efficiency furnace? I'm on a limited budget as my wife stays home with our 2 little ones. I only plan on keeping this house for about 7 more years as I'll eventually outgrow it (I bought it last year).

If I get a 90+ Eff furnace, is it safe to still use the b vent for the water heater? The Home inspector told me last year I might need to replace the water heater if I get a high efficiency furnace. He told me about the old furnace before purchasing it, and it still runs, but will need to be replaced by this winter.

Thanks for reading and the advice!
Old 05-19-18, 02:02 PM
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I think that these questions are best answered by your local building dept (Rochester Bureau of Buildings & Zoning 585-428-6526) as codes vary from place to place. Ask which mechanical code they're using and if there are any local amendments. Many/most residential water heaters come with a 3" draft diverter, so one would hope that the mfg was able to determine the correct size, and that's what I've used as a sizing guide for venting. Here I can use a common vent for water heaters and forced-draft furnaces, but it may not be the same there.

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