On Jan 31, 5:46*pm, wrote:
On Mon, 31 Jan 2011 12:42:05 -0800 (PST), wrote:
On Jan 31, 1:54*pm, wrote:
On Mon, 31 Jan 2011 02:10:08 -0800 (PST), wrote:
On Jan 30, 2:27*pm, wrote:
.
Supposedly is the key word here. * According to whom, exactly is an
80% efficiency furnace suddenly 85% efficient, depending on how
it's installed or used?

First of all, it is NOT an 80% efficient furnace. It is an 80+%
efficiency furnace, and test documents the dealer had showed it to be
approxemately 85% efficient when running in the mode mine is running
in (timed low burn) with the specified temp rize across the heat
exchanger etc. Since the company that installed it 8? years ago is no
longer in business I cannot ask for copies of that documentation.
It included all kinds of stack temperature and stack airflow
measurements as well as gas-flow measurements.

It's an 80%+ furnace, just like the 90, 93, or 95 furnaces are 90+,
93+
95+. * Meaning that they are all capable of a wee bit more. * But it
doesn't mean your 80%+ is anywhere near the efficiency of a 95.

I'd also be VERY skeptical of the "dealers" reading of spec sheets
and associated claims.
I can show you plenty of threads where "dealers" are making all
kinds of stupid claims. * I was looking at one the other day where
a guy with 31 years of experience in HVAC was endorsing direct
vent furnaces because using colder outside air results in a lower
flue gas temperature, resulting in higher efficiency..... * WTF?
That's completely wrong and defies not only physics, but common
sense.

I was not dealing with an "idiot" dealer.

Since he believes that a two stage furnaces becomes 5% more efficient
when running at the lower firing stage, I'd say that he could meet
that qualification.

He didn't say that, and nor did I. I said it is an 80+ % efficient
furnace, which he stated is likely running closer to 85% than 80%

Let me refresh your memory. Here's exactly what you said:

" And the 80+% efficient furnace is supposedly running about 85% as
installed -"

And you said the dealer said this:

" It is an 80+% efficiency furnace, and test documents the dealer had
showed it to be
approxemately 85% efficient when running in the mode mine is running
in (timed low burn) with the specified temp rize across the heat
exchanger etc."

So forgive those of us who are totally confused at this point. Is
that furnace
that the manufacurer spec'd at 80% really running at:

A - around 85%

B- closer to 85% than 80%, ie at least 82.6%

C - closer to 80%, which is what the Berkley study I cited shows?



By your own words, it cannot be an 80% efficient furnace because you
said one of the differences between an 80% and a 90% or higher furnace
is the presence of a draft inducer blower - WHICH THIS FURNACE HAS.

I made the mistake of assuming that 80% furnaces don't have a draft
inducer.
I'm wrong on that point. I just looked at one online and it has one
too. But
that detail is a distraction, because it only makes your apparent
advocacy
of an 80% two stage furnace more difficult to defend. The only
difference
left between that furnace and a 93% or 95% furnace today is the latter
has
an additional heat exchanger and costs about $250 more. The cost
differential easily recovered by the 16% reduction in fuel costs.
Even if
your fuel bill is only $500 a year, you'd recover it in 3 years and
then be
ahead. And that is without rebates from govt, utilities, etc. For
many
people, that makes the 95% furnace less expensive from day one. You
can't get a rebate that I know of from anyone for an 80% furnace.

Yeah, I know, that extra heat exchanger could fail, but since they are
covered
under long warranties, like 25 years, seems like a reasonable risk to
me.
You have yet to answer that simple question, which goes to the core of
the
issue:


Say we have a guy with a 2,000 sqft home, living in say Ohio. Would
you
say he should buy an 80% furnace today, or a 95% furnace?



*Did you read the Berkely study? *Can you show me
any study, data sheet, etc that says a two stage furnace, produces 5%
more heat from the same amount of gas as a single stage? * If it is
so,
why don't the manufacturers put it in the specs of the furnace?
Example: * Model XGQ090 *90,000 BTUS, 95% efficient using *first
stage,
90% using second stage. * Would be a hell of a selling feature, no?

There is a small but measurable difference in OVERALL efficiency with
a furnace that runs longer at a time, therefore having fewer purge
cycles and fewer warm-up/cool-down cycles than a "larger" furnace.

I believe the EPA test methodology includes that. And oddly, the
Berkely
study came to the conclusion that two stage furnaces actually benefit
from the current test methods, which they said do not accurately
reflect
actual two stage operation. The new proposed test method, which
Berkley believes more accurately represents two stage operation
shows no efficiency advantage to two stage. None...




The rating of the furnace at 80+% means the furnace will excede 80%
efficiency in any approved installation. High fire, Low fire, timed,
or dual stage thermostat. If it will excede 80% (say for arguement
81%) in a marginal installation, where it is significantly if not
grossly oversised and run on high fire only, it should/will excede 83%
if properly sized to the house/heat load.(on high fire or low fire).
And I don't care what kind of math you use, 83% is closer to 85% than
it is to 80%



Lets' assume the above is true, and the two stage furnace is 83%
efficient in some installations, Then using the same exact
arguments,
the 95% furnace has a slightly higher potential output too. So
what?
83% is still a long way from say 97% and the latter will save about
16% on fuel