for those with homes

The Value of A High Efficiency Home Furnace

June 22, 2006 07:08 AM - John Laumer, Philadelphia


“Is a high efficiency furnace worth it”? That’s the question
posed by Kim, one of our readers. From a technology standpoint, we
scanned this overview by “HomeTips.com" and decided there are too
many options to offer a yes or no answer. A few efficiency points
added to millions of home furnaces would result in a large cumulative
cutback in greenhouse gas emissions; and, hopefully, much money
saved. But, is it worth that outcome to discard millions of perfectly
good furnaces, taking a chance on newer technology, of unknown
reliability? Could there be unintended consequences? Lets start with
an assumption that your existing furnace burns natural gas or
propane, is quite old, and operates near or below the low end of the
“name plate” efficiency range of modern furnaces. Unfortunately,
if you burn oil, and have no access to natural gas, there is not much
can be done in the way of high efficiency furnace technology. If
thats' the case, skip to the next post!

If you have access to gas, numbers first. Get three or more directly
competitive bids. Ask each bidder to give you one estimate for a
“budget” system, of high reliability, but low capital cost; and
another bid for a high efficiency furnace. Ask for detailed line
items in the bids, and be certain to ask that the exact Annual Fuel
Utilization Efficiency (AFUE) rating be included on each furnace listed.

If a bidder gives you line item details on one system and not the
other, tell him to try again. Rule of thumb: unresponsive bidders are
the unlikely to provide reliable cost estimates.

Choose bid(s) you like: one high and one low. What is the installed
cost difference between them? Is it hundreds; or is it thousands? If
it’s a few hundred, the decision can rest on reliability.

If the installed cost difference is thousands, you’ll want to know
that the payback period is relatively short for the high performing
furnace. OEM furnace makers usually supply guidance on expected cost
savings. Check their web sites.

For a ‘back of envelope’ projection of annual fuel savings of the
high-end model versus the low-end model, figure out what your fuel
bill was last year. Although even the “budget” system likely could
do substantially better than your existing furnace, use your actual
fuel consumption for a “conservative” baseline. Considering that
the weather and fuel prices are both fairly unpredictable, and likely
to be less predictable in the future, this is about as good as you'll
be able to do with fuel cost basis for your comparison.

Calculate the incremental annual savings of the high-end system by
direct proportion. Here’s a hypothetical example:

79% AFUE budget system
-------------------------- * Last year’s bill = lowered fuel bill.
97.% AFUE high end system

0.814 * $2,400/yr = $1,954 (sample calcultion of fuel expense last
year with new high efficiency v.s. the new budget system for the
duration)

Incremental savings with the high end system would have been just
over $400/last year.

If you can find a furnace model comparable to your existing one and
it has a modern AFUE rating on the sticker (likely to be under AFUE
60), run the calculation again to see what the improvment would be
from your existing, to a new high end model. (In the hypothetical
example calculated savings would have been close to $900/year
assuming a 60 AFUE number for the existing furnace.)

Looking over the process diagram for the high efficiency condensing
gas furnace (see illustration), one of the odd things, both
environmentally and aesthetically, is that the existing chimney would
be abandoned, as only a small plastic pipe is needed to discharge the
cool, dry exhaust. Tearing down the chimney would be an added cost
that would certainly change the look of a building -- some would say
detrimentally. You'd at least want to see that any exterior chimney
bricks be re-used. Or just have it plugged and left in place.

The plastic pipe used for exhaust has has to be corrosion resistant
and very well could be vinyl: not an issue for this writer but some
may find it 'compromising.' Also needed is a condensate discharge
pump and line. Apparently the high efficiency gas furnaces discharge
several gallons of combustion produced water per day. Because natural
gas should be relatively free of metals, it may be possible to at
least consider using the condensate discharge as a feed for things
like toilet flushing, depending on corrosivity.

Bottom line: if the investment pays for itself in 5 to 10 years and
you can afford the cost, its all good for the worlds climate from the
first time you use it until end of its operating life.

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