I'm in the market for a new gas high efficiency furnace (93% or higher efficiency w/ variable speed fan). I have a few "issues" and i've gotten a few opinions but I'm still not sure what to do.

Situation is this: House is a 1980 ranch in Wisconsin with exposed/finished basement, original gas furnace (106k BTU I think). Approx. 2,400 finished square feet. New windows in the late '90s. House lost 1,350 cubic feet/minute in a blower test.

Issue #1: I was told my 3 year old gas water heater isn't venting properly (i.e. letting some carbon monoxide into the house), probably due to location (long angled run before getting to chimney). I was told a chimney liner "might" fix this.
Issue #2: Normal installation of a new high efficiency furnace is out the side of the house, but there is no good place to do this, the only option possible would be to put it out right under a wood deck (and right where we might want a sunroom built someday).

Question 1: One of the two contractors I talked to said that if I were willing to buy a power vented water heater w/ 2" pipe, he could run that and the new furnace venting pipes up the existing chimney and out the roof. I hate the thought of having to buy a new water heater, but I like the idea of using the existing chimney for everything.
Is this acceptable to put them vertical through the roof? (I thought those normally have to go out the side of the house)

Question 2: One contractor said 60k BTU would be more than adequate for our house, and another said he would feel more comfortable with 80k BTU. As a dumb homeowner, how do I decide? There is a possibility we might want to add on a few hundred square feet in 5-10 years. Any advice on sizing given the house info above?

Sorry for the long post but I wanted to give as much info as possible for the 2 questions. Considering the high $ cost and how long I'm going to be stuck with this system, I want to make the right decision. Thanks for any advice you can give!

Hi John,

Both vents would need unrestricted venting, so under a deck/room may not be acceptable. I have power vented furnace and heater and I like it from the standpoint that I'll never have to worry about my chimney again.

Have you called MG&E and see if you can get them to do an assessment of what size furnace you need?

Back again

Around a year ago, I had a guy come to the house and do an assessment of the energy efficency of my house. In a nutshell, it sucked. Bad. They house is old, wasn't insulated, etc. They gave me lots of good inof on what to imporve, what to not worry about, etc.

The cost was about $300 if I recal but they also helped me out with rebates on the things I had done. There's all sorts of stuff you can get $ back on. ie. - a high eff. water heater can net you a rebate of $250. A new gas HE furnace - $150, etc.

THis is their web site

http://www.homeperformancetesting.net/

And I dealt with a guy named Mark who really knew his stuff.

John,

The contractors should have run a "Load Calculation" on your house to see what the proper size unit is needed. The vertical run of a chimney needs to be a minimum of 2 times the length of the horizontal run for proper draft. Yes they can run the 2 units up your chimney. Be sure these units get inspected by your local municipality or city so you know it was done correctly and safely, plus your sure that the contractor is properly licensed. Like Kurt said your local energy company can assist you with some off these things.

Thanks for the replies. I actually had that same testing done (it wasn't Mark, it was the other guy). That's how I learned my water heater wasn't venting properly.

It's just a tricky situation because of the water heater problem and especially because there really isn't any good place to side-vent these things in our house due to the design of the house.

The funny thing is the energy specialist calculated a 60k furnace would be appropriate, but one of the contractors (who was recommended by the energy specialist) disagreed with the 60k. I should just have them talk to each other since they know each other!

I'm not so hung up on the 60 vs 80 but I just want to make sure that taking these out the roof is acceptable practice. Maybe I will call MG&E and/or the town building inspector to make sure that is ok with code.

A properly burning gas appliance does not produce any carbon monoxide under normal operating conditions.
Depending on % of surrounding air dilution, slight spillage of carbon dioxide from the water heater into a large unconfined area is probably nothing to worry about.

Now IF the appliance is in a confined area without enough make up air to dilute the carbon dioxide it is possible that it can start breathing it's own exhaust (carbon dioxide) and the second time through it will be carbon monoxide.

All furnaces come with installation instructions with examples of different ways to terminate their flue exhaust pipes and fresh air intake pipes (if they have one)

On my furnace, I have a type "B" furnace flue pipe going up the chimney with the water heater exhaust going up around the outside of the furnace flue pipe.
Of course all furnaces are not exactly the same and each individual appliance's installation instructions MUST be followed.

I would also question the ability to run the vents, and the intakes, up the chimney - that's might be a fairly long run for power vent units.

Each manufacturer of HE power vented units have specifications on how long the intake/exhuast runs can be, and the number of 90* and 45* bends factor into the overall distance. Pushing the gases vertically for the majority of the run is harder than pushing up them horizontally. Reason is that the exhaust gases are realatively cool coming out of the HE units (you probably won't have this issue with the water heater unless it too is a HE unit).

I'd start with the manufacturers intake and exhaust run length charts, and see what each (Furnace and Water Heater) says about vertical runs.

Dan