What Is a Furnace Draft Inducer Blower? I'll tell you what it is ...

[Home Guy]

It's another component that can fail on you on the coldest night of the year, over a holiday weekend, fouling up your vacation or christmas plans.

Tell me if your precious, modern furnaces with their ECM fan motors save electricity when they also have to have these draft motors running.

Hmmm. Here's a PSC (!) draft motor, consuming 80 watts. I hope you're factoring in this 80 watts into your furnace's electricity use.

And also note the reference to "government-mandated efficiency standards". Like I said before, the modern furnace being sold today is not the result of pure market-driven competition from a design and construction point of view.

These blowers were not necessary on old furnaces. However, once the government mandated furnace efficiency standards beyond what natural convection could handle, the draft inducer was created. This enabled specific control of how much air moved through the heat exchange unit. That, in turn, made it possible to determine BTUs and the AFUE and, thus, the unit's efficiency.

Crock of shit.

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What Is a Furnace Draft Inducer Blower? By Arlene Miles, eHow Contributor updated: June 25, 2010

A furnace draft inducer blower is a relatively new component of modern furnaces that became part of heating units after government-mandated efficiency standards were enacted. The draft inducer blower's purpose is to move air and gases out of the furnace and up through the chimney. This component determines how much and how fast air will move through the heat exchange unit.

Housing

Although variations occur, typical draft inducer blower is located in the gas burner compartment of a furnace and consists of a motor-driven wheel assembly or fan, an electrical box for power connections and a metal sleeve surrounding the assembly. Variables include size of vent pipe diameter, voltage, amperage, wattage, horsepower, and size of the cutout needed for the unit.

Manufacture

Draft inducer blower components are made of durable plastics and metals, or a combination of both. Polypropylene is used to manufacture industrial draft inducer blowers used in corrosive environments because this plastic resists corrosion better than other materials and will never delaminate. Fiberglass is also used when the component must withstand temperatures above 220° F. Blower size is determined by the size of the unit in which it is located.

Purpose

As the furnace enters start-up mode, the draft inducer blower begins to purge the heat exchanger of gases that may have remained in that area during the furnace's previous heating cycle. This makes the air in the area cleaner at the time of combustion and also prevents furnace burners from becoming clogged with soot. By improving the quality of air moving through the furnace, the draft inducer blower helps improve efficiency of the system.

Operation

When a furnace begins a new cycle, the draft inducer blower fan begins whirring 30-60 second before the furnace burners actually ignite. The fan motor must also run properly and usually has a safety pressure switch connected to the fan housing. Pressure switches ensure that the motor is running according to the manufacturers' specifications. If the inducer fan motor cannot turn on, the furnace will generally shut off and lock out. Several other reasons may also cause the draft inducer blower to ultimately shut down a furnace. These include a faulty pressure switch, a bad rubber tube component, or there may be a blockage in the gas vent flue, or even the blower itself may not be working properly.

Replacement

Because many draft inducer blower models are nearly impossible to rebuilt, an entirely new unit must be purchased in most cases when one wears out. The exceptions to this rule, according to Furnace Parks USA, are units manufactured by Carrier and Bryant.

[.p.jm.]

Hate to break this to you, Homey, but the type of blower motor has nothing to do with the presence or absence of a draft inducer motor.

[Steve]

If you don't like it, then go to work for one of the manufacturers and show them how *you* think it should be done.

BTW... draft inducer motors are *NOT* PSC motors, and the inducer motors in some furnaces are DC.

In any case, kwitchurbitchin and go away.

[The Daring Dufas]

What? You don't like entertainment? :-)

TDD

[Steve]

Gettin tired of playing with this one.....

[clare]

You, with all your gabbing, have still not explained WHY a draft inducer is REQUIRED on today's furnaces.

With the high efficiency of today's furnaces, too little heat goes up the chimney to reliably create a proper draft in the chimney to be sure exhaust gasses are properly vented. The "eductor" fan starts before the flame is lit and gets air moving up the chimney, and it continues to run at high speed untill the flame has created hot enough gasses to maintain draft. The eductor motor in IN the exhaust, just like the power vent on a gas water heater.( at least it is on mine - there are apparently others that use forced air into a sealed combustion chamber.

[clare]

And the draft inducer motor can be single speed PSC, dual speed PSC, or dual or variable speed ECM.

[The Daring Dufas]

I understand entirely. :-)

TDD

[clare]

And some ARE PSC motors

I'll agree there.

[hrhofmann]

What is/are PSC and ECM? I have a 50 year-old furnace that is more efficient than some of the new ones after I modified the flame to use

1/2 the gas it originally used.

[The Daring Dufas]

Did you keep the same BTU output? ;-)

TDD

[Home Guy]

I bet he did, because by reducing the flame his duty-cycle is probably longer (just like a modern furnace).

Obviously if his house is reaching the desired temperature as called for by his thermostat, then his furnace must be putting out the required amount of BTU's over time.

Reducing the flame is as simple as turning the dial on the gas regulator in the furnace, or partially closing the gas shut-off valve on the line going to the furnace.

Increase the efficiency even more by reducing the combustion-air intake baffles (the round disks mounted on the front end of each burner). These are usually set wide-open. By closing them down so that they're about 1/6 to 1/8 open, you reduce the amount of combustion air that can be pulled into the burners, and you "slow" the flames down by doing that (you slow the speed of the updraft) which means less heat is wasted up the flue.

Turn them down to the point where you just see a little bit of red / orange in the flames.

[Smarty]

Lowering the inlet gas pressure and adjusting baffles is not improving efficiency, generally speaking. The heat exchanger operates at differing efficiencies depending upon how much heat is applied and how much heat is removed, very much dependent upon blower speed, burner output, and the actual design of the exchanger itself. The heating and cooling rates of the exchanger and the heat anticipation in the thermostat should be matched to the building thermal time constant and homeowner preference in terms of how much swing in temperature is acceptable. Obviously very short burner cycles at high temperatures will make bigger spikes than longer, lower temperature burns with higher blower speeds / longer blower cycles.

I find it ludicrous to accept the notion that a 50 year old furnace claimed above can be made more efficient than a modern design, and moreover, even more ridiculous when the further claim is made that the efficiency gain was made by turning down the gas without making other, much more drastic modifications.

Fifty year old forced air furnaces have some nice things to recommend them, but efficiency is not one of them, and certainly not in the 95+ percent range being achieved since the mid-1980's by condensing furnaces.

[.p.jm.]

That's not 'efficiency', that's 'fuel input ( and heat output ). Totally diffferent issues.

[.p.jm.]

Are you actually supporting his theory that he increased his efficiency ?

You are truely clueless. You think burning an over-rich mixture is somehow 'efficient' ??? It's actually just the opposite.

[Black Dragon]

What "Home Guy" suggested there strikes me as potentially dangerous if not lethal. An over rich mixture creates a much higher percentage of deadly gases (carbon monoxide / dioxide) as well as other issues that can severely effect systems such as soot and acidic condensation. No?

Are you adjusting a furnace or an oxy-acetylene torch? Sheeze. Suggest shut your pie hole before somebody takes your ridiculously bad advice and kills their family.

[.p.jm.]

Yes. While burning the fuel LESS efficently, not MORE.

[Home Guy]

By turning down the gas supply, his furnace is reducing it's BTU output and is also reducing the internal temperature of the heat exchanger. His fan blower is not changing the amount of CFM of air being pushed through the exchanger.

Heat exchanger efficiency (any heat exchanger) is not constant over a range of differential temperature (ie - the temperature difference between the incoming house-hold return air on one side of the heat exchanger, and the combustion air on the other side of the exchanger).

For example, if the combustion-air temperature is 300F, and my incoming household air is 60F and 1000 CFM, I might get an efficiency of 80% at extracting the heat of that 300F combustion air and transfering it to my

60F incoming air, boosting it by 20F giving me 80F coming out of the furnace.

On the other hand, if I turn the burners up so the combustion air is now

500F, my incoming household air is still 60F, it's still being moved through the furnace at 1000 CFM, and maybe it's coming out of the furnace at 90F. But my efficiency has dropped to maybe 70%.

This effect is probably more prounounced in the old-style furnaces with long horizontal burners where the combustion air really doesn't spend a lot of time in the furnace and has a low resistance path directly up the flue.

And no, there is no way that a 50-year-old single-stage furnace can approach the 90%+ efficiency of a modern 2-stage unit, but that's got everything to do with a completely different burner and combustion galley arrangement, a longer combustion path, more surface area, thinner heat-exchanger walls, etc, and nothing to do with using an ECM motor or electronic pilot or a computer in the furnace.

The point is that by reducing the BTU output of an old furnace, you are allowing the heat exchanger to operate more efficiently, and you are reducing the potential payback in getting a new furnace, and you are increasing perceived comfort by having a more constant heat-output from the furnace instead of short spikes of high heat followed by long periods of cool-down.

Go and look at any old furnace and you'll likely see those baffles wide open, and possibly even see the restrictor disks removed completely. Because back when those furnaces were installed, the price of natural gas was a pittance, and nobody adjusted those disks with a combustion meter.

I'm not saying to close them completely, but I am saying that their current position is probably wide-open which is also not correct in terms of operating efficiency. And especially if you turn the burners down to half or even a third of full output (which my 120k btu unit currently is, which works fine even at 15F outdoor temperature) then closing the restrictor disks has an even more beneficial effect on efficiency.

Which, without having a combustion meter, is a good approximation of a correct mixture.

[Home Guy]

If the air balance and pressure differentials in your home, furnace and flue stack is such that there is potential for combustion gases to back-draft and enter the house-hold air, then you have a potentially dangerous situation *regardless* how the air mixture or gas regulator is set.

[.p.jm.]

You, sir, are an asshole.