Hi, I work for a small fireplace business and all most all of the broschures I hand out give an efficiency rating; however only some are a.f.u.e. rated whats the difference? What does a.f.u.e. stand for and can you you explain this to me in a way that would be easy to tell my customers? Thank You
A.F.U.E. RATING VERSUS EFFICIENCY RATING
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" The AFUE is the most widely used measure of a furnace's heating efficiency. It measures the amount of heat actually delivered to your house compared to the amount of fuel that you must supply to the furnace. Thus, a furnace that has an 80% AFUE rating converts 80% of the fuel that you supply to heat -- the other 20% is lost out of the chimney.
Note that the AFUE refers only to the unit's fuel efficiency, not its electricity usage.
The US Department of Energy (DOE) determined that all furnaces sold in the US must have a minimum AFUE of 78%,"
"AFUE (government efficiency) ratings can be off by 25% or more, an error that can under-estimate fuel consumption by up to 47%.
The study shows that a consumer who purchases a home heating system based only a comparison of AFUE ratings may actually spend as much as $800 per year more on fuel with one system, compared to a second system with a nearly identical AFUE rating. This difference in real efficiency is determined by a characteristic of all heating systems called idle loss, a performance factor which is not evaluated for AFUE determination. Idle loss includes two primary areas of heat loss on conventional home heating systems: standby loss, and jacket loss. Also almost entirely neglected are draft regulator and room air losses.
In the study, the reduction of idle losses is identified as a primary factor in improving real system efficiency. Only when idle losses are reduced or eliminated is it possible for real efficiency to approach the AFUE rating of a heating product. In fact, significant idle losses may lead to actual efficiencies as low as 55%. This “real” efficiency rating may determine system performance even when the government AFUE rating is established in the 80-90 percentile range. "
Note that the AFUE refers only to the unit's fuel efficiency, not its electricity usage.
The US Department of Energy (DOE) determined that all furnaces sold in the US must have a minimum AFUE of 78%,"
"AFUE (government efficiency) ratings can be off by 25% or more, an error that can under-estimate fuel consumption by up to 47%.
The study shows that a consumer who purchases a home heating system based only a comparison of AFUE ratings may actually spend as much as $800 per year more on fuel with one system, compared to a second system with a nearly identical AFUE rating. This difference in real efficiency is determined by a characteristic of all heating systems called idle loss, a performance factor which is not evaluated for AFUE determination. Idle loss includes two primary areas of heat loss on conventional home heating systems: standby loss, and jacket loss. Also almost entirely neglected are draft regulator and room air losses.
In the study, the reduction of idle losses is identified as a primary factor in improving real system efficiency. Only when idle losses are reduced or eliminated is it possible for real efficiency to approach the AFUE rating of a heating product. In fact, significant idle losses may lead to actual efficiencies as low as 55%. This “real” efficiency rating may determine system performance even when the government AFUE rating is established in the 80-90 percentile range. "
AFUE=Annual Fuel Utilization Efficiency
This takes into account such things as jacket losses, standby losses (pilot) and such things
Regular (steady state) Efficiency is usually only taken when the unit is up and running and does not take everything into account.
Therefore, AFUE is usually LOWER than the steady-state.
When it comes to wood and pellets stoves, I don't think many manufacturers test or publish AFUE - which can fool the customer big time. Example: A fireplace insert claims 70% efficiency - BUT, that is from tests then the unit if freestanding, NOT in a fireplace. Put the unit in an exterior fireplace, and it is possible the AFUE could be 15-20% lower. Now you can see why they don't test and publish this data!
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Extra Info....
Taking a oil boiler, for example. Regular efficiency is usually calculated simply by the stack temp, percentage of gases in the stack and by the smoke (or lack of). But if this boiler had terrible insulation and lost 20% of it's water heat into the unheated basement, that would not be figured in. AFLUE would take all this stuff into account.
A big loss for oil equipment is heat sucked up the stack when the unit is off - again, this is calculated in AFUE, but not in a standard efficiency test.
This takes into account such things as jacket losses, standby losses (pilot) and such things
Regular (steady state) Efficiency is usually only taken when the unit is up and running and does not take everything into account.
Therefore, AFUE is usually LOWER than the steady-state.
When it comes to wood and pellets stoves, I don't think many manufacturers test or publish AFUE - which can fool the customer big time. Example: A fireplace insert claims 70% efficiency - BUT, that is from tests then the unit if freestanding, NOT in a fireplace. Put the unit in an exterior fireplace, and it is possible the AFUE could be 15-20% lower. Now you can see why they don't test and publish this data!
----------------
Extra Info....
Taking a oil boiler, for example. Regular efficiency is usually calculated simply by the stack temp, percentage of gases in the stack and by the smoke (or lack of). But if this boiler had terrible insulation and lost 20% of it's water heat into the unheated basement, that would not be figured in. AFLUE would take all this stuff into account.
A big loss for oil equipment is heat sucked up the stack when the unit is off - again, this is calculated in AFUE, but not in a standard efficiency test.
Craig is right about stack loss when the burner is sitting idle.. I have made this suggestion before to have an automatic or motorized damper.
It is wired into the ignition and opens before ignition. After the eshaust gasses are removed the motorized damper closes and holds heat in the furnace/ boiler
It really eliminates the iddle loss of heat being drawn out of the burner up the chimney.. This is one way to increase the effeciency of existing burners.
Another way is a fire retentioner. and to set the timing cycly of the oil feed Just like a car default settings are not the most effecient
there are ways to improve and increase effeciencies. other than buying a new furnace /boiler
It is wired into the ignition and opens before ignition. After the eshaust gasses are removed the motorized damper closes and holds heat in the furnace/ boiler
It really eliminates the iddle loss of heat being drawn out of the burner up the chimney.. This is one way to increase the effeciency of existing burners.
Another way is a fire retentioner. and to set the timing cycly of the oil feed Just like a car default settings are not the most effecient
there are ways to improve and increase effeciencies. other than buying a new furnace /boiler
I would tend to worry about the motorized flue damper failing to open and allow gas passage. It would be unfortunate to CO your whole house.
That's a pretty easy fix though Highbeam, make sure the burner can't light until that damper is open.
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