Yes, but my understanding is the furnace
manufacture calculates the heater efficiency
without taking required ventilation (draft) into
account. So when you compare a gas furnace which
requires a certain amount of ventilation to an
electric furnace which requires no ventilation,
The results are skewed in favor of the gas furnace.

Bob wrote:
Heaters have two different types of efficiency ratings. One is called steady
state efficiency, and one is called seasonal efficiency.


The only way to rate a heater is under laboratory conditions. If you take
the exact same heater, and install it in two different homes, the season
efficiency will change, depending on run time. Natural draft through a
vented heater will cool it down when it isn't running.

The draft you are talking about is considered "infiltration", and is taken
into account during a heat loss/gain calculation. It has little to do with
the efficiency of the heater.



"George E. Cawthon" wrote in message
...

m Ransley wrote:

Right OP didnt say what his lpg heater is so how can you figure a
comparison without knowing its efficiency. Im sure its as efficient as
Ng and there are many types and ratings so he could have junk running
40% efficiency or a ventless 99% or furnace at 60-94.5% eficiency
Electric is 100% efficient.


One thing that bugs me about gas furnace/heater
efficiency is how they calculate it.

My gas furnace is 80 percent which I assume means
that the 80 percent of the BTU's in the gas end up
in the house side of the heat exchanger, i.e,
useable heat.

But I don't think they ever consider the heat loss
from the the vents. How many BTU's are lost
through the the two openings of 100 square inches
each, one at the floor and one at the ceiling.
The flow of air through these vents is continous
24 hours a day. The furnace may put 80 percent of
the heat into the house, but how much heat is lost
through those vent openings? The greater the
difference between inside temperature and outside
temperature, the greater the total heat loss.
Maybe that is why they don't estimate that loss.

I could imagine that at 0 degrees, as much as 50
percent of the heat could be lost. In other
words, at 80 percent AFUE furnace would actually
result in only 40 percent of the heat retained in
the house compared to Electric heat which would be
100 percent since no vents are used.