Water heater vent choice suggestions

Jeffrs

Hello all. Moved into my now current home about a year ago. Looking for opinions on what venting options make sense. 

Water heater is a 40 gal atmospheric vent tank type, orphaned into a 8x8 clay tile flue. I can see that I’m getting some back draft, but not enough to set the CO alarm off. Water heater is 7 years old anyway so planning it’s replacement soon and my venting options. 

Not looking to going to a larger gas meter, as they might require a repipe into the house, so a tankless condensing unit is out of the plan. 

Was originally planning on dropping a stainless flue liner in and then running another atmospheric vent, but wanted to compare my other choices.

I don’t want to do direct vent, as direct vent non power requires punching thru the block foundation, which I’d prefer to avoid if possible. 

And finally, could do a power vent with pvc out the side of the house just above the sill, however a power vent unit adds at least $650 or more to the cost for a comparable atmospheric unit, and I’m limited on my venting locations out the house where the water heater is currently located. 

I’m leaning towards the atmospheric vent as I like that it opens up more available options, the ability to change out the unit with whats available at the big box stores if needed to be replaced in an emergency, and the unit will still heat even when the power is out. However, it seems that the consensus online is that atmospheric venting will disappear soon, which if it does, will negate the need for the  flue liner  in future water heater replacements. What’s your guys thoughts?
Thank you all. 

Larry Weingarten

Hi, How about running some B vent in the existing flue? A 40 gallon heater should need three inch vent pipe. Change anodes regularly in the tank and it will give you many years.

Yours, Larry

Or just go with a heat pump water heater...