I’ll get to the actual installation story in a bit, but first I’d like to give you some history. Our original furnace was never completely up to the job. It was under-powered as far as I'm concerned, as is quite possible in new homes, where the basement is undeveloped. I believe that the calculation did not account for a fully developed living area in the basement. That, coupled with the fact that our house is long and narrow, caused our home to be cooler at each end. We tried to make the bedroom warmer using a vent fan, but that just created an imbalance in the system, and we stopped using it after a few days. So, one thing I wanted to be sure of, was that our next furnace was sized correctly for our home. In case you’re wondering why I had to replace the furnace at this point, the symptoms it was exhibiting indicated three possible causes, all of which would be expensive, with no guarantee it would work. We had already replaced pretty much every part in the furnace except for the heat exchanger. For me, that was the point of no return. Furnace issues weren't just limited to us either. We’ve seen a furnace repair truck parked in front of every house on the block over the years more than a few times.
So as you may know, a mid-efficiency (80%) furnace vents the exhaust out a metal chimney, typically to the roof. A high-efficiency furnace does not. Instead, it vents the much cooler exhaust through PVC plastic pipe to an outer wall and out. It also typically requires a separate pipe for combustion air to come in. In some instances, they can use a special 2-in-1 pipe that does both.
It was the venting options that caused me the most confusion and worry. It seems that every time I asked a different professional what my options were, I got different sets of answers. Ultimately, what is possible is limited by local codes. These codes change over time. This worked in my favour apparently, because some options I was told about lately were not even legal five years ago.
Venting out the side of the house presents some challenges in a modern home, because of proximity to your neighbour and your own existing vents, services, windows and doors. You can’t vent exhaust gas anywhere near a door or window. Nor can it be near any fresh air intake vent. Nor can it be near the natural gas inlet pipe. In many houses, that doesn’t leave many options, especially if you’re in a duplex like we are, because one wall is already off limits (the shared wall) and in our case, another wall was off limits because of the porch and another wall is possibly too far from the furnace. Then there’s the combustion intake pipe. It can’t be near any type of exhaust vent, including the dryer vent.
There is another venting option, but it involves the existing chimney space. This is great when the wall(s) just aren’t giving you the clearances you need between vents, windows, etc. They can run pipes up the chimney, but this requires room in the chimney space and it probably requires pipe that can handle the heat from the metal stack. That means more expense. If you’re now only going to be using a hot water heater up the stack, it also probably means putting a liner or a smaller metal stack, because using a full sized metal stack is going to be too big for just one little hot water heater. More money. Never mind that they’ll need access to the chimney space from inside the house, which means cutting holes in the interior walls.
Sometimes the salesman / estimator will tell you some things are possible, making you feel great. Then the installer comes over and tells you the real story, and you have to make some snap decisions.
In my case, I was lucky, but it required some creative manoeuvring. I had space on my side wall for the furnace exhaust vent, but I was also trying not to open up the finished ceiling between the furnace room and the outside wall. Fortunately, there was wide open ceiling in my basement just a few feet over and we followed that route to the outside. The next issue was my combustion air intake pipe. I had no space on the wall other than where I had finished ceiling in the basement. So I asked if they could use the existing fresh air intake that the old furnace used, terminating at the furnace side wall. For the model of furnace I was buying, the answer was ‘yes’. No cutting into the ceiling required!
If I had decided that I also wanted to get a tank-less hot water heater, this would have posed an additional problem, because we would need a vent or two for that as well.
The only thing left to deal with was putting a liner in the existing chimney to reduce the diameter for use only by the hot water heater.
So I guess the moral of the story is that if a high-efficiency furnace is in your future, ask around. Get a few differing opinions. Examine every option that exists under current code and make sure you ask what each option means in terms of extra cost and cutting into walls and ceilings. Be sure to hire a professional that knows code well and arranges to get the permits and book the inspection. If you don’t like what you’re hearing, get another opinion.