Water Heater Vent

My plumber assured me that a vent made of 4" PVC running out through the roof would be sufficient to vent a tankless hot water heater and a furnace in my 1700 square foot home. The plumber has since disappeared and I'm having a bit of trouble finding a suitable tankless heater. The heater will service a standard kitchen and 2.5 bathrooms, one of which will have a pretty nice shower (body sprays, hand wand, large capacity shower head). My question are, will PVC be a sufficient material to use as a vent and does anyone know of a water heater which can share a 4" vent with the furnace ?
Thanks, Curt
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It's my understanding that the tankless units require a stainless steel, individual vent, not combined with other gas appliances (under pressure). They can terminate horizontially however, out therough the sidewall. PVC would melt and cause a fire of course; your plumber is an idiot.
Try your local Menards, Lowes or Home Depot. Cost will run around a grand (may qualify for a $300 Home Energy-Efficiency Improvement Tax Credit however.)
"crhras" snipped-for-privacy@sbcglobal.net wrote in message

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Thank you for the response. This week I have learned quite a bit about water heaters, venting and clowns.

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