Question
We have a wood furnace that requires a thermostatically controlled fan.
Technically we should not have a fire in the furnace if the electrictity
is off.  This year we have had numerous power outages every day and
sometimes have full roaring fires going just when the power goes off.
Here is the question:  Is it possible to use an alternative power source
for the fan?  I used to live with 12 volt power and am wondering if it
would be possible to hook up a 12 volt system with a DC-AC inverter
(cost?) to run the fan when the “grid” is down?  We had thought of a
generator but the fan does not run continuously so that is not possible?
No one around here has any ideas of what I am talking about or where to
get info…..ideas/names/addresses/feasibility would be appreciated.
Please email me privately as I don’t usually read this newsgroup.  Thanks

Answers
I think that this would be easy to do.
What you need is a DC to AC inverter.

This inverter would be connected permanently
to the battery and fan. I think they cost less
than $70us(?) for the small size that you need.
Try looking in automotive parts stores or the
local discount store. Make sure that the size
it is sized large enough to run the fan.

Next you need a good quality battery charger
to continuously charge the battery. This charger
must be of the type that can remain connected to
the battery permanently.

Last you need a deep cycle battery. I would suggest
a trolling motor battery as they are cheep and
won’t actually be used very much.

Associated Should Fan Be On When Furnace Is Off Question: I hear a humming noise from my furnace when I try to turn the fan on, what should I do?
I have Lennox furnace and whenever I turn on the fan without air conditioning, I hear a humming noise and the fan doesn’t spin. But whenever I turn on the air conditioning the fan is running fine. Also, when I turn off the air conditioning, the fan continues to run normally. So every time I want to turn on only my fan, I would have to turn on the A/C on and turn it off again. Any suggestions? Thanks.

• Answer:HVAC Tech.: The hum you hear might be the purge blower running, this should happen first in the light up process. the sequence is staged so that the purge is first, the unit lights off, when it heats up enough the blower comes on and warm air comes out. When the heat setting is reached the fire goes out, then as the thing cools down then the blower turns off last. Hope that helps you!

Associated Should Fan Be On When Furnace Is Off Question:Motor Fan in force air unit does not turn off?
I have a force air unit (gas heater & AC) where everything works find except in the heating mode. In the winter the gas furnace goes on and heats the house properly. Normally when the house reaches the right temperature, the gas burners shuts off and the fan motor should continue to run for about a minute or until the furnace cools off. The problem that I have is that the motor fan in the unit does not shut off (even after the unit has completely cooled off) and continue to run indefinitely. The only way to shut off the motor fan is to the turn off the unit at the thermostat from the “heat position” to the “off” position. I have replaced the thermostat and this did not fix the problem. I have the feeling that there is heat sensor in the gas unit that has gone bad, but I don’t know where to look for this sensor or what this senor mite look like, Can anyone help me fix this problem? The fan motor continues to run even if the fan switch is in the “auto” poistion.

• Answer:Check druid’s suggestion, but if it’s not that it may be a faulty relay. Newer furnaces have control boards with mini-relays on them (which frequently fail). Most techs simply replace the entire control board because labor costs prohibit repairs to the faulty part.

Associated Should Fan Be On When Furnace Is Off Question:HVAC fan run every so often even when is system is turned off. What can cause this?
The thermostat (White Rogers) has two settings for the fan (auto and on). Right now, the fan it is set to auto. It has another switch with three settings (i.e. cool, off, heat) and it is set to off. The fan still comes on for a few minutes every now and then. Since, the system is set to “off” and the fan is set to “auto”, the fan should not come on at all. The furnace works perfectly and when I turn on the heat it turns on the fan too. So there is nothing wrong with the system other than this fan running every so often. Here is what I have tried so far: Changed the batteries in the thermostat. Changed the air filter. Reset the thermostat to factory setting so that it is not programmed. .

• Answer:My answer only applies if your furnace is gas and if it is an older furnace. There is a control on the furnace called a fan/limit control. I have a link to what the control might look like below. The control brings on the blower during a call for heat. When the burners fire, the control delays the blower coming on until the heat exchanger gets warm enough. The fan/limit control has a 5, 8 or 11 inch probe that protrudes into the heat exchanger area. The probe contains a bi-metal spring that expands, causing the dial on the control to start turning. When it reaches the temperature setting on the control, a switch is engaged causing the blower to run. When the burners shut down, the bi-metal spring cools and contracts, then the dial turns the other way until the switch is disengaged, causing the blower to turn off. If your furnace is in an attic, the heat from the attic can cause the probe to get warm, expand and engage the switch, causing the blower to run for a few seconds until the probe cools off. The bi-metal probe is either getting weak or the settings on the dial need adjusting.

Associated Should Fan Be On When Furnace Is Off Question:Why are the burners in my Amana furnace not turning back on when the temp goes below the thermostat setting?
The gas burners turn themselves off when the house reaches the set temperature, as they should, however, the fan stays on, but the burners do not turn back on when temperature falls below the thermostat setting. I can only get the burners to go back on if I turn off the power to the furnace and switch it back on. The igniter seems to be fine.

• Answer:sounds like the control board. when your shutting off the power your basically resetting the board, if it was a fan limit the fan would not come on at all, unless your furnace is very old you wont have a thermocouple and you did state that your ignitor was fine. depending on the model of furnace you have the board will cost between 100 to 250 dollars. i have a carrier and the board for it was listed at 269.00

Associated Should Fan Be On When Furnace Is Off Question:Why is my furnace cycling on / off?
Ok, here’s the real story, I fix things for a living but I get stumped once in a while. My own home’s forced air gas furnace is giving me a run around. A few years ago, I installed an electronic pilot ignition system in it to replace the original standing pilot. I also raised the size of the blower fan pulley a little to try to boost performance. The ignition has worked flawlessly ever since but I have subsequently lowered back the pulley size..too noisy etc. The issue is, mostly in cold times, when the (digital) thermostat calls for heat, the ignition triggers, flame detection responds and main valve fires…all normal. The main burner continues for awhile heating the box until the temp / fan switch raises and triggers ultimately starting the blower…again all normal. Then, once the blower is running, while watching the temp / fan switch, it slowly begins to lower (presumably because the blast of cooler / cold return air coming into the box). Unfortunately it continues and gets to a point where it then shuts the blower back off to keep the unit from blowing cold air into the house. The burner stays on…never goes out…because the thermostat is still calling for heat. Then, we wait for the box to again raise in temp (remember burner is still on) to a point where the temp / fan switch will once again raise and turn on the blower moving warm air into the house….but also cooler / cold air back to the box via the return duct. The cycle continues, blower on for a little bit, temp sensor gets cooled by incoming air, blower shuts off….repeating on, and on, and on, The temp / fan switch was replaced a couple of years ago. Filter is new…actually no filter right now, but access door for the filter is sealed shut to prevent outside air from entering the return duct. The high limit setting on the temp / fan switch it is about 180 to 190….it never gets to that point, The trigger on (fan on) set point is about 125 to 150, the trigger off (fan off) point is about 65 or 70. The burners look good…but all I can think of is the unit is not putting out the level of heat it should and can’t keep up with the temp of cooler air returning back to it. In thinking about this, I think the problem has been occurring probably since the conversion to the electronic ignition (maybe before) which included a new main combination valve. I am thinking of bringing PG&E in to look at the flame to see if it seems too low…but in my years of working on every kind of equipment around…including many furnaces…the flame looks fine to me…short bright blue flame rising about 3/4″ from the top of the burner with a longer tail of blue and yellow raising 4 inches or so above that. Maybe it needs to be higher…I am not familiar with a level adjustment of the flame on the control valve…just the air mixture via the burners adjustable air dampners. OK experts…got any suggestions?

• Answer: This Question has not been answered yet! Send us Your best should fan be on when furnace is off Answer!

Associated Should Fan Be On When Furnace Is Off Question:The fan on my gas furnace is running constantly, and the heat is not coming on either. Why?
The pilot light is on, but the unit still does not light up like it should. I am not sure if the fan is on all the time because it is just trying to bring the room up to temperature. I have done everything including: 1. Turn off the thermostat, then turned back on 2. Turned off the switch on the furnace that seems to turn off the fan. 3. Turned off the furnace by turning the gas switch to the off position. 4. Reset the breaker in the house. Not sure of the age of the unit, but definitely under 27 years old since that is when the house was built.

• Answer:The problem is that you have a limit switch opened on your furnace.. Which causes the fan to run constantly and wont let the gas valve open. Some limit switches are auto reset others are manual reset which means you must reset it yourself. Take the front cover off of the furnace. Look against the back part where all the electrical parts are. First turn the breaker off please. With out knowing the exact furnace just start looking at all the electrical componets and push any buttons you see on them you will know when you hit the right one, it will click. Turn the power back on and set your t-stat this should solve the problem

Associated Should Fan Be On When Furnace Is Off Question:My house smells like burnt oil from furnace. Please help?
I have lived in this house about 3 years and have had my furnace serviced every year. The problem is the service tech can never seem to find out or care about the smell just as long as its efficient 85%. I have a Beckett furnace and burnham boiler with the forced air exhaust out the side of the foundation. It seems the smell is the worst whenever the furnace is not working. There is no oil leak. When i stand over the boiler, it seems to smell like oil coming out of it. What could be causing this? Unburned oil sitting in there between firings? The exhaust fan not on long enough and air coming back in? How long should the exhaust fan operate after the furnace shuts off?

• Answer: This Question has not been answered yet! Send us Your best should fan be on when furnace is off Answer!

Associated Should Fan Be On When Furnace Is Off Question:What might have caused my gas furnace to quit? What questions should I ask the repairman?
This morning my gas furnace (Trane) suddenly quit and made a sound like a dying propeller engine on a plane. When I tried to restart it (I set the thermostat to hold at 72 degrees and turned it on ‘Auto’) the inducer fan came on and about 10 seconds later the burners started. At that point the inducer fan and the burners suddenly cut-off. The furnace then tried to restart itself (unsuccessfully) every few seconds. I’ve called a professional but I want to make sure I’m not getting over-charged. What are the possible problems and what questions should I ask the technician?

• Answer:This unit does not have a thermocouple. It sounds to me like the impeller in the inducer motor has shed a blade or two. If the impeller losses a blade or two then it may provide enough draw to make the pressure switch but not once the hot flue gases start rolling through it. Here in Ohio, that repair would cost you roughly $325.00

Associated Should Fan Be On When Furnace Is Off Question:Furnace Will Not Ignite-Fan still Runs?
My furnace will not ignite. It doesn’t even sound like it is trying to ignite-as if it is not even getting a signal from my thermostat. Here’s the thing, my fan keeps running. Even when I shut my entire system off from the thermostat, the fan continues to run, My inside temp is 66 degrees and the thermostat is set to 72, so the heat should kick on, but it doesn’t. I have an electronic ignition electrode that sparks to ignite the pilot, which in turn lights the burners…however the spark is not present, not even the sound of it trying to spark. Should I replace the spark ignition electrode, or should I start with the high temp limit control Sensor/switch? I have had several people tell me its the circuit board, but I don’t think its that. The fact that the ignition assembly isn’t even firing is telling me maybe the limit switch was shorted somehow or is old and needs replacement. Please advise and thanks for the help!

• Answer:Sounds like a bad relay. The signal from your thermostat is not being recognized. It could easily be the circuit board because it works off of 24 volts. But, its your money.

Associated Should Fan Be On When Furnace Is Off Question:Why is my central air / furnace freezing / icing up?
The part that is icing over is the pipe that goes from the furnace outside to the central air unit. I had it checked by a professional and I was told that my pressures & freon levels are fine. My filter was changed a week ago. However, it was rather dirty when it was removed. The professional told me that he didn’t know what was wrong. He said my central air unit is rather old. Therefore, I need to buy a new central air unit. My furnace is less than a year old and I am afraid that if it continues to freeze, it is going to hurt my furnace. I turned my furnace off with only the fan running for over 24 hours. It appeared to be completely thawed out. It iced back up once I turned on the air conditioning again. What should I do? Is it possible that the central air unit is fine (since it is maintaining the correct pressure and freon levels)? Is it possible that the pipe going from my furnace to my central air unit just needs replaced? Thank you for your replies. The furnace is new so I wouldn’t think that it would need a good cleaning yet, would it? The furnace is under warranty so that is why I have to use the company that told me that he didn’t know what the problem was. If I call another company it may void my warranty. How would I check the coil for dirt?

• Answer:Good thing there is a 30 percent tax credit on new ones this year. Usually freeze ups are caused by low levels of freon. Could be your professional didn’t want to work on old unit. Maybe a second professional opinion is in order?

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