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  #1   Report Post  
NewGuy
 
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I do not know much about furnaces, but to me it looks OK that blower motor
runs longer, because your furnace already heater heat exchanger, blower
still blows into your house leftovers of the heat.


"RZ" wrote in message
...
I have a Lennox natural gas furnace, model G24M3/4-100A-2 with
electronic ignition. The furnace was installed new in 1994, and I see from
a
service log that the burners and inducer were serviced in 2002, and the
inducer was replaced one month later, after the servicing. We live in
Canada, where this furnace is heating for 5 months of the year.
I don't know if I have a problem or not,but the blower motor seems to
run on longer than the burn period. So, you end up with unwanted cool air
blowing out of the heat registers, and a blower motor that is running an
electric bill up, unnecessarily.
Here is a run-down of a complete cycle:
1. thermostat sends signal to furnace to heat home
2. flue fan starts, and runs for 45 seconds
3. burners ignite, and burn continuously
4. blower motor starts 45 seconds after burners ignite
5. thermostat sends signal to furnace that ambient temperature is 1 deg
warmer than set desired temperature
6. flue fan stops and burners shut off simultaneously
7. blower motor continues to run for 3 minutes
8. blower motor shuts off
I was told by a furnace repairman, over the phone, that the problem is
most likely the pressure-switch, and it should be replaced. This
pressure-switch is an easy DIY replacement, and would cost me $40, but
before I go ahead and get a non-returnable switch, and find out that I
still
have the blower running longer than the burn cycle, I want to know if this
is the normal operation for this furnace. And, is there anything else I
should be looking for, before I have to get a repairman to come have a
look
for $60/hr.

Does anyone have any experience with these furnaces, and what would you
suggest?

Thanks







  #2   Report Post  
David Efflandt
 
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On Wed, 17 Nov 2004 11:58:33 -0600, RZ wrote:
I have a Lennox natural gas furnace, model G24M3/4-100A-2 with
electronic ignition. The furnace was installed new in 1994, and I see from a
service log that the burners and inducer were serviced in 2002, and the
inducer was replaced one month later, after the servicing. We live in
Canada, where this furnace is heating for 5 months of the year.
I don't know if I have a problem or not,but the blower motor seems to
run on longer than the burn period. So, you end up with unwanted cool air
blowing out of the heat registers, and a blower motor that is running an
electric bill up, unnecessarily.
Here is a run-down of a complete cycle:
1. thermostat sends signal to furnace to heat home
2. flue fan starts, and runs for 45 seconds
3. burners ignite, and burn continuously
4. blower motor starts 45 seconds after burners ignite
5. thermostat sends signal to furnace that ambient temperature is 1 deg
warmer than set desired temperature
6. flue fan stops and burners shut off simultaneously
7. blower motor continues to run for 3 minutes
8. blower motor shuts off
I was told by a furnace repairman, over the phone, that the problem is
most likely the pressure-switch, and it should be replaced. This
pressure-switch is an easy DIY replacement, and would cost me $40, but
before I go ahead and get a non-returnable switch, and find out that I still
have the blower running longer than the burn cycle, I want to know if this
is the normal operation for this furnace. And, is there anything else I
should be looking for, before I have to get a repairman to come have a look
for $60/hr.


What pressure switch. It is normal for a thermostat inside the furnace to
wait to kick on the fan until the heat exchanger is warm (so you do not
get such a blast of cold air) and run on after the wall thermostat turns
off to extract remaining heat until the heat exchanger is not so hot.
But if you get cool air during shutdown, the shutoff on that internal
thermostat for the furnace fan may be set too low or not functioning
properly. So have the repairman check the fan thermostat in the furnace.

I am not an expert, just grew up with oil scorched air furnace in the 50's
(my brother now owns the home and replace it with a gas furnace).
  #3   Report Post  
Joe Fabeitz
 
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RZ,
It's normal for the fan to run for a short time after the fire goes out.
This is to distribute the remaining heat in the heat exchanger. In older
systems, the fan (blower) was controlled by a temperature sensor near the
heat exchanger. At the beginning of a heat cycle, when it sensed the fire
had heated the exchanger enough, it started. At the end of a cycle, after
fire, it remained on until exchanger had cooled a bit. Some newer furnaces
use electronics ( a timer) to determine how long it runs. Btw, you may want
to measure the temp. coming out of a heat register. Moving air feels cooler
than it actual is. You may find the apparent "cool" air is actually a few
degrees warmer than the room air, in which case you don't have a problem.
Newbie heat pump users experience this phenomenon because they expect
"warmer" air to be expelled, similar to a gas (or oiled) fired furnace.

I'll go out on a limb here and say the "bad pressure switch" idea is bogus.
Usually the pressure switch is used to verify the blower is blowing. If it
is not, the fuel is cut off to prevent the heat exchanger from overheating.

"RZ" wrote in message
...
I have a Lennox natural gas furnace, model G24M3/4-100A-2 with
electronic ignition. The furnace was installed new in 1994, and I see from

a
service log that the burners and inducer were serviced in 2002, and the
inducer was replaced one month later, after the servicing. We live in
Canada, where this furnace is heating for 5 months of the year.
I don't know if I have a problem or not,but the blower motor seems

to
run on longer than the burn period. So, you end up with unwanted cool air
blowing out of the heat registers, and a blower motor that is running an
electric bill up, unnecessarily.
Here is a run-down of a complete cycle:
1. thermostat sends signal to furnace to heat home
2. flue fan starts, and runs for 45 seconds
3. burners ignite, and burn continuously
4. blower motor starts 45 seconds after burners ignite
5. thermostat sends signal to furnace that ambient temperature is 1 deg
warmer than set desired temperature
6. flue fan stops and burners shut off simultaneously
7. blower motor continues to run for 3 minutes
8. blower motor shuts off
I was told by a furnace repairman, over the phone, that the problem

is
most likely the pressure-switch, and it should be replaced. This
pressure-switch is an easy DIY replacement, and would cost me $40, but
before I go ahead and get a non-returnable switch, and find out that I

still
have the blower running longer than the burn cycle, I want to know if this
is the normal operation for this furnace. And, is there anything else I
should be looking for, before I have to get a repairman to come have a

look
for $60/hr.

Does anyone have any experience with these furnaces, and what would you
suggest?

Thanks







  #4   Report Post  
Joseph Meehan
 
Posts: n/a
Default

RZ wrote:
I have a Lennox natural gas furnace, model G24M3/4-100A-2 with
electronic ignition. The furnace was installed new in 1994, and I see from
a
service log that the burners and inducer were serviced in 2002, and the
inducer was replaced one month later, after the servicing. We live in
Canada, where this furnace is heating for 5 months of the year.
I don't know if I have a problem or not,but the blower motor seems to
run on longer than the burn period. So, you end up with unwanted cool air
blowing out of the heat registers, and a blower motor that is running an
electric bill up, unnecessarily.
Here is a run-down of a complete cycle:
1. thermostat sends signal to furnace to heat home
2. flue fan starts, and runs for 45 seconds
3. burners ignite, and burn continuously
4. blower motor starts 45 seconds after burners ignite
5. thermostat sends signal to furnace that ambient temperature is 1 deg
warmer than set desired temperature
6. flue fan stops and burners shut off simultaneously
7. blower motor continues to run for 3 minutes
8. blower motor shuts off
I was told by a furnace repairman, over the phone, that the problem is
most likely the pressure-switch, and it should be replaced. This
pressure-switch is an easy DIY replacement, and would cost me $40, but
before I go ahead and get a non-returnable switch, and find out that I
still
have the blower running longer than the burn cycle, I want to know if this
is the normal operation for this furnace. And, is there anything else I
should be looking for, before I have to get a repairman to come have a
look
for $60/hr.

Does anyone have any experience with these furnaces, and what would you
suggest?

Thanks


It is normal, in most modern furnaces, for the blower motor to continue
to run for some time. It would also be normal for the air coming from the
register to "feel" cool towards the end of this cycle. Just as a fan makes
the air "feel" cool it has not cooled it. Since your furnace should be
taking air from the room, running it through the furnace and then returning
it, it will not be cooling the air (ignoring the possibility of the ducts
running through a non-heated area). When working as intended, you will save
more in fuel cost by recovering more heat, than you will pay in electricity
to run the fan.

Now that said, there may be some adjustment possible to reduce the time
it runs. That time may be governed by a timer or by a ttemperature sensor
in the furnace. I have not checked to see what mine does, but as I recall
it is based on a timer and I have never looked to see if there is an
adjustment. It would be possible your thermostat could control it but I
don't think they do.

My advice is to enjoy the extra circulation and efficiency.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math



  #5   Report Post  
Walter R.
 
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Default

The run-on is normal in order to extract all heat from the heat exchanger.

In my furnaces the run-on is adjustable. It is a small switch box on the
outside of the furnace with a probe reaching into the hot air plenum. It has
a temperature dial (primitive) with two pointers. One pointer sets the temp
when the furnace blower will come on and the other one when the blower is
supposed to turn itself off because all hot air has been extracted from the
heat exchanger.. There is a small difference between the two settings. You
may be able to change the run-on at this dial, if your furnace has one.

If you set the run-on too short (shut-off temp too high), the blower will
turn off but will then turn itself on again briefly to pump any remaining
heat into the house. But, since the air in the ducts will have cooled off in
the meantime, you get a lot of cool air blowing into the house.

Just experiment until you get it perfect.

--

Walter
The Happy Iconoclast www.rationality.net
-

"RZ" wrote in message
...
I have a Lennox natural gas furnace, model G24M3/4-100A-2 with
electronic ignition. The furnace was installed new in 1994, and I see from
a
service log that the burners and inducer were serviced in 2002, and the
inducer was replaced one month later, after the servicing. We live in
Canada, where this furnace is heating for 5 months of the year.
I don't know if I have a problem or not,but the blower motor seems to
run on longer than the burn period. So, you end up with unwanted cool air
blowing out of the heat registers, and a blower motor that is running an
electric bill up, unnecessarily.
Here is a run-down of a complete cycle:
1. thermostat sends signal to furnace to heat home
2. flue fan starts, and runs for 45 seconds
3. burners ignite, and burn continuously
4. blower motor starts 45 seconds after burners ignite
5. thermostat sends signal to furnace that ambient temperature is 1 deg
warmer than set desired temperature
6. flue fan stops and burners shut off simultaneously
7. blower motor continues to run for 3 minutes
8. blower motor shuts off
I was told by a furnace repairman, over the phone, that the problem is
most likely the pressure-switch, and it should be replaced. This
pressure-switch is an easy DIY replacement, and would cost me $40, but
before I go ahead and get a non-returnable switch, and find out that I
still
have the blower running longer than the burn cycle, I want to know if this
is the normal operation for this furnace. And, is there anything else I
should be looking for, before I have to get a repairman to come have a
look
for $60/hr.

Does anyone have any experience with these furnaces, and what would you
suggest?

Thanks









  #6   Report Post  
Dr. Hardcrab
 
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Default

You have described a furnace that runs exactly the way it should.

Besides, a blower motor does not use that much electricity. In fact, many
people run theirs 24/7.


"RZ" wrote in message
...
I have a Lennox natural gas furnace, model G24M3/4-100A-2 with
electronic ignition. The furnace was installed new in 1994, and I see from
a
service log that the burners and inducer were serviced in 2002, and the
inducer was replaced one month later, after the servicing. We live in
Canada, where this furnace is heating for 5 months of the year.
I don't know if I have a problem or not,but the blower motor seems to
run on longer than the burn period. So, you end up with unwanted cool air
blowing out of the heat registers, and a blower motor that is running an
electric bill up, unnecessarily.
Here is a run-down of a complete cycle:
1. thermostat sends signal to furnace to heat home
2. flue fan starts, and runs for 45 seconds
3. burners ignite, and burn continuously
4. blower motor starts 45 seconds after burners ignite
5. thermostat sends signal to furnace that ambient temperature is 1 deg
warmer than set desired temperature
6. flue fan stops and burners shut off simultaneously
7. blower motor continues to run for 3 minutes
8. blower motor shuts off
I was told by a furnace repairman, over the phone, that the problem is
most likely the pressure-switch, and it should be replaced. This
pressure-switch is an easy DIY replacement, and would cost me $40, but
before I go ahead and get a non-returnable switch, and find out that I
still
have the blower running longer than the burn cycle, I want to know if this
is the normal operation for this furnace. And, is there anything else I
should be looking for, before I have to get a repairman to come have a
look
for $60/hr.

Does anyone have any experience with these furnaces, and what would you
suggest?

Thanks







  #7   Report Post  
TURTLE
 
Posts: n/a
Default


"RZ" wrote in message
...
I have a Lennox natural gas furnace, model G24M3/4-100A-2 with
electronic ignition. The furnace was installed new in 1994, and I see from a
service log that the burners and inducer were serviced in 2002, and the
inducer was replaced one month later, after the servicing. We live in
Canada, where this furnace is heating for 5 months of the year.
I don't know if I have a problem or not,but the blower motor seems to
run on longer than the burn period. So, you end up with unwanted cool air
blowing out of the heat registers, and a blower motor that is running an
electric bill up, unnecessarily.
Here is a run-down of a complete cycle:
1. thermostat sends signal to furnace to heat home
2. flue fan starts, and runs for 45 seconds
3. burners ignite, and burn continuously
4. blower motor starts 45 seconds after burners ignite
5. thermostat sends signal to furnace that ambient temperature is 1 deg
warmer than set desired temperature
6. flue fan stops and burners shut off simultaneously
7. blower motor continues to run for 3 minutes
8. blower motor shuts off
I was told by a furnace repairman, over the phone, that the problem is
most likely the pressure-switch, and it should be replaced. This
pressure-switch is an easy DIY replacement, and would cost me $40, but
before I go ahead and get a non-returnable switch, and find out that I still
have the blower running longer than the burn cycle, I want to know if this
is the normal operation for this furnace. And, is there anything else I
should be looking for, before I have to get a repairman to come have a look
for $60/hr.

Does anyone have any experience with these furnaces, and what would you
suggest?

Thanks


This is Turtle.

If i can remember right the G24 Series has this type fan delay system. I would
have to look it up in my service manuals but i'm too lazy to go see.

The Lennox model that you have has a set timer for how long the blower motor
will run after the cycle of heat has ended. You can select 60 sec. [ 1 minute ]
, 90 seconds [1.5 min.] , 120 seconds [ 2 minutes ] , or 180 seconds [ 3
minutes ] for it to run after the cycle is over. You can find this pin type
sellector on the relay board of the furnace and you pull the plastic pin out and
shove it down on the 120 sec. or the 90 sec. pins to get that time for it to run
after the heating cycle is over. i DO NOT recommend running it lower than 90
seconds for your waisting fuel / heat by doing so.

Awwwwwwwww, You / Serviceman says The pressure switch has something to do with
the after cycle fan staying on. The pressure switch is a safety switch that
shuts things down and not keep things running. One of two thing is going on
there. I'm missing something here or somebody is bull****ting somebody.

Also I can't see it from here, for you have your car parked in the way.

TURTLE


  #8   Report Post  
RZ
 
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Default Lennox Furnace Run-on

I have a Lennox natural gas furnace, model G24M3/4-100A-2 with
electronic ignition. The furnace was installed new in 1994, and I see from a
service log that the burners and inducer were serviced in 2002, and the
inducer was replaced one month later, after the servicing. We live in
Canada, where this furnace is heating for 5 months of the year.
I don't know if I have a problem or not,but the blower motor seems to
run on longer than the burn period. So, you end up with unwanted cool air
blowing out of the heat registers, and a blower motor that is running an
electric bill up, unnecessarily.
Here is a run-down of a complete cycle:
1. thermostat sends signal to furnace to heat home
2. flue fan starts, and runs for 45 seconds
3. burners ignite, and burn continuously
4. blower motor starts 45 seconds after burners ignite
5. thermostat sends signal to furnace that ambient temperature is 1 deg
warmer than set desired temperature
6. flue fan stops and burners shut off simultaneously
7. blower motor continues to run for 3 minutes
8. blower motor shuts off
I was told by a furnace repairman, over the phone, that the problem is
most likely the pressure-switch, and it should be replaced. This
pressure-switch is an easy DIY replacement, and would cost me $40, but
before I go ahead and get a non-returnable switch, and find out that I still
have the blower running longer than the burn cycle, I want to know if this
is the normal operation for this furnace. And, is there anything else I
should be looking for, before I have to get a repairman to come have a look
for $60/hr.

Does anyone have any experience with these furnaces, and what would you
suggest?

Thanks





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