"Pete C." wrote:

John wrote:

"Pete C." wrote:

John wrote:

"Pete C." wrote:

Robert Gammon wrote:

Todd H. wrote:
"Martik" writes:


Are you referring to the chimney for the furnace? Why would anyone put
something in there. Sounds like a good way to murder someone! Luckily we
have 2 CO detectors.


Birds have a nasty habbit of not informing homeowners of their nesting
plans. If only the birds would follow the permit process, by god,
lives would be saved.


Given that the top of the stack is a protected entrance, it will be
DIFFICULT, but not impossible for small birds to get in there. The gap
to my fireplace is a bit larger than my furnace flue, and small birds do
find their way to the fireplace from time to time. In 28 years, never
such an incident in either gas water heater or gas furnace.

A maintenance worker sticking a rag down the flue and forgetting to take
it out seems to be a more likely scenario. such an action is more
likely to occur at the bottom of the stack, at the furnace, rather than
on top of the roof.

A large percentage of chimneys do not have screened caps. Raccoons
nesting in open chimneys are not unheard of.

Chimneys? Modern efficient gas furnaces do not require "chimneys." They use
ordinary piping to bring fresh outside air in (so you're not sending your heated
home air into the combustion chamber to throw away) and remove exhaust.

The same applies to modern efficient oil furnaces though they do not use
PVC pipe for those vents.

What is the efficiency rating (AFUE) for these "modern efficient oil furnaces?" My
natural gas furnace is about 96% efficient (AFUE), meaning that about 96% of the
energy in the gas becomes actual heat in my house. How does your "efficient oil
furnace" compare?

Well, no, it means that the furnace sends 96% of the energy in the gas
to it's output as heat, whether that actually becomes heat in your home
is dependent on other factors. A good oil fired boiler I looked at was
86.8%, I don't have numbers handy for oil furnaces at the moment. Again,
there are multiple reasons to choose oil over nat. gas.

Not true. Heat that goes up the chimney or out the exhaust is not included in AFUE. It
would make AFUE pretty pointless if the heat being measured in its rating wasn't used to
go into the distribution system. (I am assuming that all heat in the duct system goes to
the house and that you aren't running ducts outside, through an ice cellar, or through a
cold attic).

"The Annual Fuel Utilization Efficiency (AFUE) measures the amount of fuel converted to
space heat in proportion to the amount of fuel entering the furnace. This is commonly
expressed as a percentage. Energy Star labeled furnaces must meet or exceed 90% AFUE
energy-efficiency ratings." http://www.waptac.org/sp.asp?id=6841