Furnace: continuous fan or auto fan

[Ron]

Here is the situation:

Natural gas furnace is 14 years old (in great shape for age according to tech) and the choice is to run either a continuous fan or auto fan. In total energy consumption (gas and electricity) which mode is more efficient. Ours is a 3 level home plus unfinished basement.

I know that with the fan running continuously the temperature throughout the house is very uniform. I feel that the auto fan setting will result in the stratification of the heat levels within the house making it uncomfortable in some areas. The wife is more comfortable with the auto setting and I prefer the continuous.

Other than the comfort levels, it is a given that if the furnace motor isn't running all the time, it will use less electricity. How will the gas consumption be affected one setting vs. the other?

[mark Ransley]

It depends on KW cost, in the midwest I pay .125 kwh .100 watt 24 x 7 is apx 10 dollars a month. My furnace runs apx 8 hrs a day and the blower takes 400 watt. Its new. An older one and a larger blower will consume more. My unit is 75000 btu. Say yours takes 500 watt. at 24 x 7 at .125 that is 50 $ a month for fan only Runnng say 8 hr avg to heat on Auto will save you 33 a month at .125 KWH cost. New variable speed motors can take only 90 watt. Will it need more heat running on auto, maybe less.

[Ron]

That is the question though isn't it. Will "auto" consume more gas than "continuous?"

[mark Ransley]

why should it consume more gas. It sholdnt

[David Efflandt]

It could. My bro-in-law heard that setting the fan thermostat lower would run the fan longer and get more heat out of the furnace air and be more efficient. So he thought he would go them one better and run the fan continuously (maybe even at the higher A/C speed).

What he was not aware of was that running room temperature air through uninsulated ducts in the outside walls resulted in more heat loss (heat transfer is most efficient when 2 objects are closest to the same temperature). The heat transfer to outside was so great, and lack of heat transfer to cold air moving quickly through the furnace, resulted in 50 degree F maximum home temperature in cold weather. Once he set everything back to normal, the air was able to be heated in the furnace and get to the rooms and get the house up to temperature.

Some people also think that removing the thermostat in their car will help it run cooler (not). The water ends up moving so fast that it does not have time to absorb or transfer heat and the engine overheats.

Heating and cooling systems have design criteria and if you go outside the envelope, things may not work like you expect.

[Stormin Mormonn]

No. Actually, maybe a trace less.

[Ron]

Snip>

Not exceeding the acceptable parameters is the trick. Having visited quite a few "heating" sites, it seems that the best situation is to have a multi-speed fan system that never goes off and increases speed when heat is applied and then drops back between cycles.

What prompted all this was a newscast about the electricity rates here in Ontario Canada going up in the spring. They then went on to the topic of conservation of hydro and one of the things was the use of the "auto" setting on the thermostat would save $X per month. The wife being the thrifty type heard this immediately and is all "gung-ho" for the auto setting. That's fine with me as long as we are not saving $X on electricity only to put out that amount or more on the gas bill.

This is a new house to us so we haven't any history of use to fall back on for statistics.

My concern is based on the "pooling" of the warm air against the ceilings with the lower areas of the rooms being cooler even though there is warm air at the top of the room. This lower temperature would then trigger the thermostat to call for more heat just to get the lower portions of the room heated to the thermostat setting.

I know that the use of ceiling fans in the summer cut into the amount of run time the air conditioner had when they were used. I am wondering if the same thing happens with the heating cycle. I have found no data to "munch" on.

We may in the long run go with the continuous fan for air quality reasons (dust collecting in filters and not floating around the house type of thing).

More knowledge makes for better decision making.

Ron

[Tony Hwang]

Hi, Good idea running dual speed fan. Hi when heat/AC is on, lo other times. Tony

[Trent©]

Have you ever done this? How many times? Has it always overheated?

Wishing you and yours a happy Thanksgiving season...

Trent

[Trent©]

HOW do you know that? Yer assuming that the blower circulates air uniformly throughout the house...and that's highly unlikely.

I honestly have never heard of anyone asking this question before. I thought everyone knew that the normal operating position for a forced-air furnace was auto. This is very interesting.

If you have a central humidifier on the furnace, how are you gonna control it? Are you gonna have it run all the time also?...wasting electricity and water?

I think a lot would have to do with the placement of the thermostat. For instance, a thermostat is usually installed in a 'living' room...and controls the entire house. So many of the rooms may be heated not because of the conditions in THAT room...but because of conditions in the 'living' room...where the thermostat is located.

If you run the blower continuously, you'll probably maintain a more median temperature throughout the house...and I don't think that's what you really want to do.

I've read ahead a little...

If yer concerned about wasted heat at the ceiling, install and run ceiling fans. You can also put them on thermostats of their own if you so desire.

Again...I've never heard of running a furnace during the Winter on anything other than auto. I certainly wouldn't want it running that way at night...when I can turn up the electric blanket and turn down the furnace. If I'm gonna keep the house at 62°, for instance, I wouldn't want the blower running. It would make the house seem awfully cold.

So...definitely not continuous.

Wishing you and yours a happy Thanksgiving season...

Trent

[Bubba]

Kind of clueless arent you Trent?

Normal? Obviously you dont get out much. Do you Trent?

Hey Trent, A humidifier is controlled by the heating circuit. The humidifier isnt supposed to run when only the fan is running. If installed and wired correctly it will only run during a call for heat, NOT a call for fan. Been hanging around a lot of hacks, have you? It wouldnt have anything to do with you being a "tight-wad" would it?

You wouldnt want the whole house to be a closer average temperature? You really arent too bright, are you Trent?

Yeah, and it looks like it hurt a lot.

A properly designed and installed heating/cooling system wont need ceiling fans to compensate for poor air circulation and temperatures.

Never? Wow, you really dont get out do you Trent? There is this interesting new concept in furnaces called 2 stage and variable speed. You should probably read up or "read ahead a littel" as you call it. Bubba

[Ron]

Thank you one and all for your responses to my query. We will be doing some experimentation to see what we want to do for the long term.

[David Efflandt]

I have never done it because I am a mechanical engineer and understand how things work.

My boss removed his thermostat for a summer highway trip and his car overheated during the trip (had never overheated before).

A friend of mine removed the thermostat from his car for wheel2wheel racing because he thought it would eliminate a device that could fail, but it fried his engine (it had never overheated in competition before). He found out afterwards that racers replace the thermostat with a fixed restrictor which limits flow to the proper range for effective cooling.

[CBHvac]

Its a simple fact. Its also a hot topic in the auto groups...no pun intended.

If you cant allow the radiator to remove the heat generated by the engine, all that happens is more BTUs are added to the coolant than is being removed, and it will overheat.

[Trent©]

I've taken out the thermostat many times...probably hundreds...over the years...only in the summer, of course.

Never had a car overheat.

So I'd say if your friends' cars overheated, they had other problems...that yer just associating with taking out the thermostat.

Wishing you and yours a happy Thanksgiving season...

Trent

[Trent©]

You need to get an education on what a thermostat actually does...and how it operates.

I've taken out the thermostat many times...never a problem.

Wishing you and yours a happy Thanksgiving season...

Trent

[CBHvac]

Actually Trent, I know full well what one does, and I hate to break it to you, but if the HVAC biz fell apart tomorrow, I could very well go BACK into automotive. I also know that on our 1948 Anglia, with a 426 in it (my hobby is building Hemi powered cars, so far, 2 Cudas, one Roadrunner, and the Anglia) has no thermostat, but it DOES have a NHRA approved restrictor in the neck...without it, it WILL overheat on a daily drive..and no...sad to say, I didnt undersize the radiator either...

Thats you, on YOUR application, under YOUR conditions. Many times in Southern CA, where road temps can reach over 150F, I would have a problem with a truck OVERheating...and it was normally due to one of the techs not telling me it overheated while on the road, (stuck CLOSED thermo) and he removed it...once the stat was back in, problem gone...and yes...I know how to determine if a leaking head gasket, timing issue, or other thing is causing the overheat condition.

Here, currently, removal of the stat wont cause an overheat on say.....a

2.5L Mopar, unless, its a long hiway trip, and not in overdrive, or 5th...higher revs, means less time in the radiator..sheesh man..its simple...it depends on the pump, the volume the pump can move, the amount of time that the system was designed to have the coolant in the radiator, and ambient temps...airflow over the radiator helps..:)

[Tony Hwang]

Hi, Removing thermostat is dumb thing to do. It off sets car engine efficiency, specially new ones under computer control. I use fail safe thermostat which will not likely fail closed. Without thermostat, no heat from heater either. Also it'll overheat rather than keeping the engine cool. Tony

[Trent©]

So...what does this have to do with a thermostat discussion? I have no doubt that what you say is probably true.

What yer saying is what *I'VE* been saying! lol

A stuck CLOSED thermostat will often cause problems. Running WITHOUT a thermostat eliminates any problems CAUSED by a thermostat...and overheating is a common problem CAUSED by a thermostat.

Wishing you and yours a happy Thanksgiving season...

Trent

[Trent©]

Not really DUMB, Tony...especially on the older cars. But not a good idea, either...except in case of emergency. I've often had to take out a stuck thermostat while on the road.

Agreed. When you take out the thermostat, it takes longer for the engine to reach optimum operating temperature. So, for that period of time, the gas mixture will usually be richer. This won't make a BIG difference, of course. But it really shouldn't be done unless necessary...road emergency, etc....especially with the newer, computerized cars.

Not true at all. All the thermostat does is change the flow of the water in the system. Once the car warms up, the flow goes thru the entire system.

Taking out the thermostat will simply make it take longer for the heater to get warm...'cause it takes longer for the water to get hot. But the heater will work as always. It will simply take longer to get that optimum heat.

This may not be true, of course, in really cold situations...where the thermostat never gets a chance to fully open.

The thermostat does NOT keep the engine cool. You can't overheat a car by taking out the thermostat.

A thermostat makes the engine run HOT. That's its purpose...to heat the water more quickly in order to get to the optimum operating temperature and to quickly get hot water thru the heater core.

It does that, of course, by preventing water from flowing thru the radiator.

Wishing you and yours a happy Thanksgiving season...

Trent