High efficiency furnace questions

Hi all,
I need to replace a 40 year old furnace in my 1100 sqft bungalow in Edmonton, Canada.
I have had several contractors come in to give me estimates and I am down to 2 companies/furnaces. Both companies seem to have good installers (as far as I can tell).
The two furnaces I am looking at are (both in the same ballpark costwise.)
Lennox G61MPV-36B-70 Trane XV90 - TUY100R9V4W (It was quoted as XV90 / 60000BTU)
And here are my questions:
- Are there good reasons to go with the one instead of the other? - Apparently my chimney needs to be reduced since only the water heater is going to be vented out there. Some contractors suggested a 4" 'chimney liner' where others suggested to use 4" B-vent. What are the differences and advantages? And is B-Vent worth 322 CAD more? - One contractor mentioned that the PVC pipe for combustion air and exhaust need to be 2" where others suggested 3" pipe. Is it true that if you have too many elbows you'll need the thicker pipe? And how important is the sloping of the pipes? - Right now I have a simple digital Thermostat "with 2 wires". Do you think it makes sense to upgrade to a 2-stage-Thermostat?
Thank you very much for your advice in advance,
Zorrolf
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configurations. My water heater and the old furnace each vented into the chimney with separate pipes. I have to assume that each had their own chimney because on the roof there are two outlets. In fact I have two chimney covers, one for each opening. My PCV pipes are 3 in. Pipe slope is important and there are installation requirements that dictate what it should be. My furnace is a 2 stage and the thermostat is one stage. What this means is that the furnace shifts into high gear after a pre-set time. The time is a variable and can be set via dip switches on the motherboard. I set mine for 10 minutes. This function (low to high) is controlled by the thermostat when it is a 2 stage stat. In my case, it wasn't feasible to run another wire from the stat to the furnace in order to get a full 2 stage system. It is a nice feature but one that I've managed to get by without. MLD
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Thanks MLD, I appreciate your reply...
Zorrolf
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diameter of intake and exhaust pipes are specified by manufacturer-- Each bend in the pipe increses resistance and so static pressure. To keep resistance in best range the diameter must be increased--
Slope is also specified by manufacterqar. to steep a slope will result in water etc. running back to furnace.

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<uriah> wrote in message wrote:

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