Any thoughts to share on hot water heater venting?

[Capsu78]

Just had my annual chimney cleaning (brick exterior on an outer wall) and got my bi annual sales pitch to make some improvements that cost $$$.  The supervisor was very detail oriented and asked if he could inspect my water heater to better understand my house venting system.  I replaced my furnace 10 years ago with a high efficiency unit that now vents out the back wall instead of up the chimney that it used to share with the hot water heater.
He said the issue with this is that it is a 9 inch pipe designed for both appliances, but as it now is only hooked up to the water heater, the gas rises but stalls in the chimney, and puts condensation on the walls.  His solution would be to run a 3 inch stainless pipe the length of the chimney... at a cost of $1750... that is a lot of unbudgeted cash for a "silent" home improvement.
He waited around to see if I would say "just do it" and when I didn't he said the other solution would be to have it revented through the outer wall, which is a lot shorter than a chimney pipe... I appreciated his honestly and might check out what that would cost.
So, has anyone ever made this decision, or wishes they would have made this decision earlier?  My fireplace is a good one- not as inefficient as some of my neighbors and friends, but I certainly don't want a major chimney replacement down the road.   

[Greg]

Whenever I've encountered appliance vents in brick chimneys it's been a problem.  The better solution for you would be to vent it out the wall.  Stainless is unnecessary unless you live right on the ocean.  Plain galvanized will likely do.

DIY if you have the skills which are using tin snips, using a 1/4" hex head driver in a cordless drill, and applying foil tape, among others.

[eil]

Venting into the chimney does sound a bit iffy to me...

Our previous house had a gas hot water heater that vented to the side of the house. Basically there's a big blower on top of the heater that collects the fumes from the top vent and blows them out through PVC pipe. Downsides are electricity consumption and noise when it's on, plus blowing some percentage of warm air out of the house in the winter. But it was totally to code and did work.

[Capsu78]

His reason for stainless was that they have to make adjustments for an offset in the chimney and he has concerns that aluminum could tear on the way down without knowing it and create a much bigger hazard.
The current system was how they built them in 1979 and living were I do they overspec codes and regulations on everything- all electrical must be in conduits etc.  The only time I have heard of people changing their venting was when air would stall and force back a burst of air that would blow out their pilot light.

[CarDude]

I don't have experience with your specific case, but I'm definitely familiar with power vented water heaters. Power vented heaters are safer than unvented heaters because the risk of backdrafts are significantly lower. The downside is that they aren't as common, so they cost more than unvented heaters. I'd definitely go with the plastic vent out the wall.

[Spork]

I just know absolutely nothing about venting an appliance through a chimney, but it sounds really ungood.™   It sounds to  me like a creosote farm -- that you have more area and more nooks and crannies to collect creosote on.

I also wondered about the stainless... but maybe that makes it more cleanable -- less scratching and places the creosote can grab onto.

[Capsu78]

Thanks for the comments... let me clarify my wording, now that I have had a chance to deep think a bit.  My chimney has 2 routes up the stack.  One is dedicated to exiting the fumes from the wood burning fireplace- yes, creosote city that we pay to clean out every year because a wood fire 4-5 nights a week from late October to early March is a pleasure we enjoy- I put way more effort into it than I need to, but my wife feels the family room is not complete on nights we don't have a fire.
The second shaft that ends at the chimney top starts in the basement, runs parallel to the chimney, and handles the vapors from the HWH only.  The gases are clean, but contain water vapors which enter the shaft at high temp which lowers as it moves up to the cap.  If its -0 outside, it starts to give off moisture which is not good for masonary.  I believe the service tech is giving me a valid concern- but I also know that Frank Lloyd Wright designed over 1600 different fireplaces, some terribly inefficient but no 2 alike...  Think I will call my HWH installer first for an opinion.

[Spork]

That at least explains a bit to me (but ... I'm totally out of my element).

We heat our house 90+% with a wood stove.  I get it.  (But I do the chimney cleaning myself... I have no idea if that is an option for you.)