I will agree with you every time, that an expansion tank is a good idea, but I've got to tell you that with almost twenty years in plumbing, it's actually pretty rare to see a hot water tank with an expansion tank. The plumbing code here in MA is one of the strictest in the country but an expansion tank is not required on a residential hot water tank. Just a vacuum breaker and drop tube on the t&p.

A majority of the hot water tanks you will see are "glass lined". That doesn't mean that there is a glass bottle inside a steel tank. It's a sprayed in liner. It helps protect the steel tank from the corrosive effects of the water. If it's not glass lined steel it's hydrostone, sprayed in cement liner, or it's a stainless steel tank. There is no reason you can't use plastic flue piping on a glass lined tank.

Actually, this is a power vent heater which just means that there is a mechanical draft. A direct vent means that combustion air is drawn from outside the building, and there is a mechanical draft. What you are thinking of would require a high efficiency heat exchanger. This water heater opperates just the same way as an atmospheric draft heater, the only difference being the mechanical draft. A instentainous water heater or a high effiency condensating bloiler would use a high effiency heat exchanger to extract most of the heat created by combustion thus lowering exhaust gas tempretures. PVC pipe actually has a pretty high heat rating. I don't remember exactly what it is.

I'm not trying to be a know it all, and anyone can tell me im wrong. I don't know much but I've been dealing with stuff like this for a while now.

 

Thanks Wittom, I knew the PVC pipe was ok, just wrong on the theory. I have seen the PVC used on forced air furnaces also.
But what do you expect out of a dumb carpenter? ha ha

 

lol,definetely not the same theory as a he furnace with 2 heat exchangers,being a hvac contractor helps

 

Hey, we know our trades. You should see the carpentry work that I did in our house. You can tell it was done by a plumber.

Dumb carpenter? You know what the electricians say to me? "If I was any dumber I would have been a plumber".

 

My favorite one is; I almost became a [ insert trade here] but they found out I could read and write, then I almost had them talked into it till they found out my parents were married!