High efficiency furnace questions

Posted by Zorrolf on November 19, 2005, 2:20 pm

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

Posted by MLD on November 19, 2005, 3:42 pm

> 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

I installed the Trane XV90 with two PCV pipes for the inlet/exhaust
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

Posted by Zorrolf on November 21, 2005, 3:04 pm

Thanks MLD, I appreciate your reply...

Zorrolf

Posted by uriah@nospam.net on November 23, 2005, 9:40 pm

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.

>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

Posted by CBHVAC on November 24, 2005, 5:19 pm

> 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--

Not to mention you left out the more important issue addressed by each
unit...TEL.
Total Effective Length.

Each 90 adds 5 feet to this.

> Slope is also specified by manufacterqar. to steep a slope will
> result in water etc. running back to furnace.

Thats why EVERY unit that is a condensing unit, requires a drain at the
unit, and in the exhaust.

>>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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