Do low-speed fans on new warm air oil furnaces run all the time?

[mm]

Do low-speed fans on new warm air oil furnaces run all the time?

How do multii-speed fans in new OIL warm air furnaces work. One webpage said that such a fan might use 200 watts, but the one speed fan my current furnace has might use 800 watts! That seems amazing.

It also gave the impression that when the furnace calls for the low speed fan, it's because the fan runs all the time. Is that right?

I'm used to the idea that very few oil furnaces have efficiency 90% or greater, and that they are very expensive. But if I get a electronically controlled fan with the furnace, that part of the furnace is eligible for the Federal Energy Credit, and I presume it's something I want to have anyhow. But I'd like to know how it works before I buy one.

Thanks.

[Don Phillipson]

Furnace fans are commonly controlled by thermostat switches with three settings: Off = fan never runs On = fan runs always Automatic = fan runs when required by the heating unit.

[The Daring Dufas]

Newer stuff with DC drive motors for the air handler may run at a very low speed continuously to even out the temperature of the home. The first HVAC system I came across with this feature had me thinking there was something wrong until I called the supplier and was assured it was a normal operating mode. The best bet is to call the manufacturer and find out if the continuous low speed is a feature of your new gear.

TDD

[Rick Brandt]

Our furnace has a continuously variable DC fan that is (as far as I know) always running. You set your thermostat fan control to "ON" and the computer manages the speed.

When not calling for heating or cooling the fan runs very slowly. You might feel a slight draft from the vent, but you could never hear it running. This was explained as helping to "even out" the temperatures within the home.

[Art Todesco]

I have a new furnace (Amana) with the Electronically Commutated Motor (ECM) inside blower. I know it doesn't run all the time. You can select continuous run on the thermostat. Also, there are different "programmable" features done my the HVAC guy like ramp up, ramp down, etc. I don't know if they can program any kind of constant run or not, but it probably depends on the brand.

[Frank]

I believe mine runs at two speeds, high and low. Wife is constantly complaining that it is not as warm even though thermostat is constant, you just don't get that blast of warm air. Told her she is welcome to turn up the heat but at $3+ per gallon she is reticent to do so ;)

[clare]

And the VAST majority of new furnace installations DO run the fan at low speed constantly when on "automatic" - kicking up to higher speeds when heat or cooling are called for. In most cases, AC blower is higher than heat blower speed.

[clare]

It is an available setting on virtually all currently available forced air furnaces - and ALL DC variable speed systems.

[mm]

After you knew it wasn't broken, did you like it? Right now, I like the total quiet that occurs at least when the furnace isn't running. Part of the year that's 80 or 90 percent of the time.

When you say "available" do you mean I could turn it off if I want to?

I don't have that now, and I've never felt the need to have the temperature evened out.

Do you mind the fan going all the time?

[mm]

Does that mean if you set it to auto, it would go off when the furnace isn't running? I like the feature you describe if I'm not stuck using it when I don't want to.

I'm afraid I might. It is a straight shot from the furnace to the big vent in the hall right outside the bedroom door, and the noise of my current fan has been a big problem. I tried changing the fixed speed on my fan, by connecting different wires, but as the schematic said, it was already on the lowest speed. I have to shut the door when I'm sleeping or trying to get to sleep.

If my temps are uneven, I either don't notice or don't mind. :)

Thanks to everyone including you, Dufas, and clare.

[hrhofmann]

Running continuously does use some electricity, but it probably cheaper than spurts of high speed whenever the plenum temperature is above the preset turn-on temperature. Due to the eveness of the temperature, you can proably set the thermostat a couple of degrees coller than normal (for wintertime use) because you won't have the temperature swings that you get with an off-on type of operation.

[Frank]

Can't remember where we set it with old furnace but when wife is cold she nudges it up. Furnace or fan does not run continuously.

I've heard similar complaints about heat pumps that don't put out a burst of heat but give even temperature control.

[mm]

That's different though. A heat pump can't put out that much heat. So I gather they run all the time when it's pretty cold, so I guess they have to run the fan too.

An oil furnace can put out plenty of heat, and even if the temp rises and falls, that don't bother me**. My main concern is if I can set the fan to go on only when the furnace is running (not counting that it starts late and stops late even now, based on I guess what hr said, plenum temperature). I want to be able to do that.

Do furnaces with ECM allow that? Because there are still plenty of oil furnaces sold that DON'T have ECM.

Thanks.

I can't ask the manufacturer easily because I haven't picked out either a furnace company or a furnace, and some salesmen will just say "Sure".

**The temp rise and fall is like a compresed version of the seasons!

[The Daring Dufas]

I first came across it when me and my buddy were servicing a newer unit some years ago. Since I wasn't in on the installation, I didn't know about the characteristics of the system. Before installing a new system, I always RTFM. 8-)

TDD

[krw]

This depends on how it's set up. My thermostat has a "continuous" setting that keeps the fan running.

The problem with heat pumps is that the temperature rise isn't enough (optimized for efficiency) so they blow much colder air than a hot-air furnace. I call mine "forced cold air heat". To compensate I have to keep the house a good 5F warmer, and that still doesn't make up for the drafts.

[clare]

Definitely. It is programmable.

I don't mind it at all. It drowns out the hum from the CFLs.

As an aside - I replaced a 30 year old standard gas furnace with a new

85%+ non-condensing 2 stage gas furnace with DC blower fan - and my gas bill did not change AT ALL. Upon investigation and questioning both the furnace people and the gas utility I found out the improved efficiency of the DC blower motor meant the blower was not providing nearly as much heat to the system, so the furnace needed to provide more - and the difference in efficiency of the burner (my old one surprised all the furnace techs who ever checked it by running 85% or better) and the heat needed to compenste for the more efficient blower fan just cancelled out. The electricity bill DID go down.

[clare]

If I turned the fan switch at the thermostat OFF the blower fan still ran at low speed. If I turned it ON, it ran constantly at high speed. If I turned it to AUTO it ran at low speed untill the furnace came on, then went to high. If I turned the furnace switch off, the blower did not run.

The new digital thermostat I have now does not have a fan control switch. Just a heat-off-cool switch, and even with it OFF the blower fan runs at low speed. If I don't want the fan running I can still throw the furnace power switch

The direct drive DC blower fan on my furnace is less than57 dB a foot from the furnace or in the next room with the door open (c scale) and does not indicate at all on the 60dB scale of my Micronta(radio shack) digital sound meter with the door closed (2 heat oputlets in the room) On the "A" scale it does not even read in the furnace room.

[mm]

Wow. What brand of furnace do you have?

Are they all like this, folks?

I don't have a sound meter, but I think I'm more sensitive to sound than average, and less sensitive to temparature changes.

[mm]

I replied before clare said that his done run all the time.

What brand of furnace do you have? Is it an ECM kind? Is it oil?

I think I want ECM, but only if I can turn the fan off entirely.

Especially if I go out of town for a week, there is abosolutely no point in having the fan run when the burner is not burning.

[Stormin Mormon]

Ideally, a furnace is matched for the size of the house, and matched to the needs. It should run nearly all the time on the winter's coldest days.