DIYbanter - View Single Post - Has anyone ever replaced their conventional furnace fan motor with anECM motor?

98 Guy

Full-quoter wrote:

I'd like to see you take any old 45+ year old furnace and make it
95% efficient.

Unless I add a second heat exchanger, no, it's not going to reach
95%. But there's no reason it can't reach 78% efficiency. Without
adding computer controls and electronic sensors.

Are furnaces today less expensive (in real dollars) compared to
10, 20, 30, 40 years ago?

I would wager that just like most other things, the answer to
your question is yes.

If "most other things" are cheaper today (in real dollars) then that
must mean we're all richer today vs years ago.

I suspect that most other "important" things are not cheaper today.

I'll bet if you look at what a furnace 40 years ago cost and
adjusted for inflation, you're getting a (...) furnace today
for a whole lot less.

Well, I welcome some hard numbers here otherwise this is just
speculation.

You're telling me it's a good thing for the environment to have
to buy a furnace every 20 years vs every 40 years?

Yes, I think it is ... Which is why they offer rebates to encourage
people to replace old inefficient furnaces with new ones.

It is not environmentally sound for me to buy a new 95% efficient
furnace that lasts maybe 15 or 20 years (instead of 30 or 35 years)
and replace it with ANOTHER 95% efficient furnace.

I'd like to see one credible referrence to anyone that agrees
it's better for the envrionment to continue to use a 40 year
old furnace or HVAC system instead of a new one.

What if that 40-year-old furnace is a 90+ furnace?

What if it's an 80% furnace?

and they can look at whatever energy alternatives are available
then. Are you clairvoyant enough to know that in 20 years
the same fuel will be the best choice? By then, the energy
situation could be entirely different

It's a no-brainer that natural gas will always be more economical vs
the only real alternative (which is electric heating).

And if we run out of natural gas in 30 or 40 or 50 years, then welcome
to the world of Mad Max and the end of civilization.

So, they had 95% efficient furnaces 50 years ago?

You don't need a furnace full of electronics, sensors and
computers to get 95% efficiency.

That doesn;t answer the simple question of whether 95%
efficient furnaces were available 50 years ago.

Like I already said, they could have made condensing furnaces 50 years
ago. I bet some were available for special situations.

And you missed the elephant in the room. For whatever reason,
that 50 year old furnace is no where near the efficiency
of one you can buy today. So, what;s your point?

I already made my point.

It doesn't take computers and electronic sensors to make a 90+
condensing furnace. It takes more heat exchangers and more "plumbing"
(ducting, etc) inside the furnace. More sealing, a closed combustion
loop, and more work at the job site to install and plumb (duct) it all
into place.

Back when natural gas was cheap, of course the industry and customers
are going to ask why build a more complicated (expensive) furnace when
the fuel is so cheap? Instead they built long-lasting, durable
furnaces.

We're not talking about AC. That's another matter.

No, it isn't. Because today most people have both as part of
one system.

It doesn't matter if the evap coil is built into a furnace or if it's
installed in the plenum above it. The AC unit is a completely
separate system that just happens to share the same ducting and blower
as the furnace. And as I've stated, it's actually inefficient to
combine the two without gating because it does add resistance to air
flow.

Are you telling us that it's also economically sound to run a 30
year old AC system that was bolted onto a 50 year old furnace

The economics of the furnace or the AC unit has got nothing to do with
one being "bolted" to the other.

If the furnace is 50 years old and if the AC unit is 30 years old then
you look at those units separately when analyzing their cost of
operation. The fact that they're "bolted" to each other doesn't
matter - the "bolting together" doesn't affect their relative
efficiencies or costs of operation.

Or that one should just replace a failed 30 year old AC
system on an even older furnace? LOL

LOL yourself.

I don't have the same hang-up that you do where you see the furnace
and the AC unit as inseparable.

But again it shows why 20-25 years is the sweet spot in terms
of system life.

As has been pointed out several times in this thread, current 90+
furnaces are struggling to achieve 15 years of service life.

I can totally understand that the average american is so strung-out
(money-wise) that hvac makers are responding by making units that
barely hang together and that builders are putting crap like that into
new construction.

But what I can't understand (if this is the case) that all hvac makers
have changed ALL of their model lines such that they no longer offer
units that absolutely will last 30 - 40 years (and then charge
accordingly for them).

Ductwork should be gated such that in the winter, air can flow
around the A-frame instead of being forced through it. And in
the summer, air should be ducted so it doesn't have to flow
through the furnace heat exchanger.

If you're so smart and know the technology and market environment
so well, why don't you go get venture capital, start a
company and build HVAC products designed to last 50 years.

Changing your ductwork as I described above is not related to changing
the longevity of the HVAC system.

I'll bet the system will look a lot like the car Homer
Simpson designed for his brother's car company and have
similar success.

The AC evap coil (A-frame) is an unneeded resistance for the furnace.
Would you like to argue otherwise?

I'll bet the system will look a lot like ...

I don't know if you've noticed, but most HVAC installations don't look
pretty when all their various lines, connections, and ducting is
finished.