On Wednesday, July 25, 2018 at 10:26:31 PM UTC-4, Ed Pawlowski wrote:
On 7/25/2018 10:14 PM, pchalas wrote:
I'm replacing my oil furnace and I'm deciding between a single stage or a 2
stage furnace w/ variable speed fan.Â* I was just wondering since my
house is
so old, will it make any difference to get a 2 stage furnace w/ variable
speed
fan? it's about a $1000 dollar difference. Thanks


While it would be good, I'd put that money toward increasing insulation.
Better payback.

If you have the money, do both.

+1

All a two stage furnace does is fire at a high output or low output.
The higher output is good because it will get the temp up faster from
being setback, when you come home and turn it on, when you've been
away on vacation and turn it on, etc. There are also wifi thermostats
now where you can turn it on from your phone, so that can also get
the temp up on the way home.

The low output is good when it's not very cold out and/or it's just
maintaining temperature. The lower firing allows the furnace to run
longer, move more air, distribute it more evenly through the whole
house. If you get a two stage, make sure you get a two stage thermostat
to go with it. A two stage thermostat, the thermostat makes the call
on which stage to use. If it knows the temp has to go up a lot, it
will call for high, otherwise it will use low. With a regular thermostat
a two stage will make the decision, based on how long it's been running.
After it's run like ~7 mins, if it's still running, then it will kick
up to high.

Variable speed blower, IMO, may be far less desirable. I don't think
fully variable speed adds much. I have an ECM, which like variable
speed, is an ECM motor. The big advantage to either is they use
substantially less electric than a conventional blower. How much
that saves depends on how much you use it and the elec rate. The downside
is that the motors have electronics in them, are more failure prone
and if they fail, instead of looking at a $150 motor, you're probably
looking at $600. I also had an ECM fan motor on the AC condenser outside.
It failed after just a few years. New one was like ~$350. I found
a conventional motor that would replace it for $90. IDK how many years
it would take to make up that difference in electric, but I suspect
it's a very long time, given the usage here. For a furnace blower in
a colder climate, the payback could be sooner, but I still suspect it's
many years. Say it's ten, is it worth it, given that if the motor fails
in six, you have to pay 4x more for a new one?