John wrote:

"Pete C." wrote:

trimmed

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).

I was referring to the losses after the furnaces heat output, not the
stack.

Bad assumptions as well since a large percentage of furnaces and related
duct work travel through unconditioned space. Horizontal configuration
gas furnaces in particular often end up in cold attics.


"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

Yes? And? As I said there are a lot of losses after the furnace output
and gas furnaces often end up in icy attics where oil furnaces almost
never do.

Pete C.