"Christian Fox" wrote in message
...
: In article
. com,

: says...
: I read somewhere that an old furnace loses its efficiency and
if its 10
: years old, it is only 55% efficient. Is this true? My furnace
is a gas
: furnace and is 12 years old.
: 1) If so, I am thinking of replacing it with a new one. What's
the best
: one out there that is 95% efficient?
: How much should I expect to pay for it and also for
installation?
:
: Unless the furnace has reached the end of its lifespan, it's
probably going to cost you a
: lot more to replace it than you'll ever save by putting in a
higher-efficiency model.
: It'd probably make more sense to wait until the furnace is
closer to the end of its life
: (it should last at least 15 years, and possibly much longer)
before you replace it.
:
: As to the costs, the only way to find out is to get some HVAC
contractors out and get
: estimates. There are too many variables involved to give you
an accurate answer.
:
: 2) Also, is it a good idea to replace my water heaters (also
gas)? Is
: it better to replace them (I have 2) with "tankless water
heaters". Are
: tankless water heaters installed in the bathrooms or can they
go in the
: basement?
:
: Tankless water heaters usually get installed in the basement
and service the whole house.
: If you have enough demand for hot water to require two regular
hot water tanks, you're
: not likely to be happy with a tankless model. Tankless water
heaters have limits to the
: amount of hot water they can produce at any given time.
:
: 3) I am thinking of adding a few more inches of insulation in
the attic
: but concerned that too much of it may lead to condensation
which could
: result in mold. Any ideas on this?
:
: You can add tons of insulation to the attic, and it shouldn't
cause any condensation at
: all as long as the insulation doesn't block the ventilation.
The attic should be vented
: at the soffits and at the peaks, creating a draft that flows
through from bottom to top.
:
: Whether the insulation will reduce your heating costs, however,
is a different story - if
: your house is only 12 years old, it probably has adequate
insulation already.
:

Many people miss the idea that insulation thickness has a point
of diminishing returns. The first few inches makes an incredible
difference. Succeeding inches add successively less heat loss
protection per each inch. Once the optimum thickness point is
reached, more insulation becomes a negligible help; other factors
become more important.
It's a logarithmic curve if that helps; rises fast, then slope
becomes gradually less and less, approaching zero (flat)
eventually. When it's REALLY cold out and touching a wall feels
resonably warm, you're at or near the point of diminishing
returns. Assuming proper installation, that is.

I know it varies by region, but I wonder what that optimum
thickness is? Anyone know? Neglecting reflective surface, etc
etc etc..
I suspect it's around 8 or 9 inches, but that's just a guess;
anything over about 6" seems to make very little difference.

HTH,

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