On Mon, 06 Dec 2010 19:49:24 -0600, "
wrote:

On Mon, 06 Dec 2010 09:29:03 -0500, mm wrote:

On Sat, 04 Dec 2010 10:15:21 -0500, Jeff Thies
wrote:

On 12/4/2010 9:01 AM, Stormin Mormon wrote:
There is a limit how creative furnace makers can get. The same basic
operating principles are used in all brands.

My experience has been to avoid Sears, and Trane. They use off
standard parts, and it's hard to get parts for them. Except to go to
Sears or Trane.

Goodman is the "discount" brand at my parts house. They have fairly
standard parts, and are inexpensive to repair. I've heaed that Goodman
is reasonable quality. The money you save on equipment costs is
signifigant.

Many folks have written that the installation is the important part.
Ask your friends and coworkers who they use. Call the company, and
have them come out for estimate. Avoid companies that manipulate,
pressure, or try to rush you into a quick decision.

Since the new system will be more energy efficient, the company may
reccomend a smaller system. It is very possible that the last company
over sized the equipment. So, the new sytem may very possibly be less
BTU and fewer tons. Many times, a smaller system will provide a lot
better comfort. The old AC may have a name plate of 4.5 tons, but
might actually be delivering 3 tons of cooling. So, a smaller system
may be needed.


How can that be? My understanding is that the rating is cooling
output, not BTU input like a furnace.

I thought furnaces were rated on BTU *output*, not input. The input
is mentioned to calculate the efficiency.

Am I right?

The ones I've looked at are rated as BTU input, primarily because they have a
fixed operating point (orifice sizes, pressures, etc.) and the efficiency
isn't well regulated.

Interesting. So do they have an AFUE rating?

The burner efficiency can be measured and the BTU
output calculated, though.

But the burner "efficiency isn't well regulated". So you mean an
instantaneous measurement of efficiency?

Or an average measurement? Isn't an average measurement made only by
looking at heat (BTU) output and dividing it into BTU input?

How can burner efficiency be measured without first measuring BTU
output? What is there about the burner that can be measured other
than BTU output?

It's not like a lever where the lengths of on both sides of the pivot
can be measured, or a gear where the number of teeth can be counted,
etc.** In cases like this, efficiency is not a real thing that can be
measured. Only input and output can be measured.

**Even in the case of levers and gears, measuring theoretical
efficiency by measuring arm length or counting teeth assumes there is
no loss due to friction or slipping. The real efficiency of a
mechancical device can only be determined by measuring input and
output and dividing one into the other.

The spec sheet I got for at least one oil furnace this year included
input and output and AFUE. If it was on the web and I can find it,
I'll post it.