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.
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.
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.
On 10/17/2010 12:48 PM, email@example.com wrote:
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-)
On Sun, 17 Oct 2010 08:51:08 -0400, "Don Phillipson"
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.
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
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.
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.
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
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.
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 ;)
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.
On 10/17/2010 5:11 PM, hr(bob) firstname.lastname@example.org wrote:
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.
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.
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
**The temp rise and fall is like a compresed version of the seasons!
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.
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