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

[Home Guy]

The intelligent reader will notice the complete absence of cogent technical reasoning in your response.

[Black Dragon]

Which is why I have trained HVAC professionals preventative maintenance my system twice per year, once at the beginning of heating season and one at the beginning of cooling season instead of listening to idiotic fuckwits who think they know what they're talking about, such as yourself on Usenet.

[Home Guy]

============================= Energy conservation guidebook By Steven R. Patrick, Dale R. Patrick, Stephen W. Fardo (C) 1993 Fairmount Press Inc. ISBN 0-88173-154-4

Page 85:

"The amount of air admitted to the burner assembly is normally controlled by a manual shutter on the front of the burner as in Fig

4-6. Adjustment of this shutter either enlarges or reduces the opening, according to it's position. The color of the resulting burner flame, as a rule, is a good indication of the resulting fuel/air mixture ratio. A yellow flame, for example, denotes insufficient primary air, whereas a sharp blue flame shows a proper mixture ratio. Burner effieciency is directly dependent upon the fuel/air mixture ratio"

I will repeat the relevant sentence:

"The color of the resulting burner flame, as a rule, is a good indication of the resulting fuel/air mixture ratio."

I will say that I was wrong about the orange color - it's yellow that you don't want to see in the flame.

Note that there is no color indication telling you if the mixture is too lean, or that the burners are pulling too much primary combustion air through the shutters.

Besides turning down your gas-valve to create a SMALLER flame, pulling the correct amount of primary combustion air through the shutters is critical in getting the best efficiency out of an old furnace. The more excess air you pull though the shutter, the faster the combustion flow will be and the less time that the flame-heat has to reside inside the heat exchanger galley and hence more of the heat will go up the flue instead of being transfered into your house.

Almost all positions of the air shutter will give you a "sharp blue flame", but only the position where it almost gives you yellow in the flame will be the correct position.

And like I said before, it's my contention that in the majority of cases, these shutters will be set wide open by default when these furnaces were originally installed - because it's a no-brainer setting that had no percieved impact on the customer and was the "safe" setting in the eyes of the HVAC technician or installer at the time.

[Molly Brown]

That=92s exactly why I still have my mechanical (no wires anywhere) wall furnace from the nineteen forties even though the state of California offered to give me one free including installation. I will still be warm even if the electricity goes out.

[hrhofmann]

No. I filled (soldered) in the gas nozzle and then redrilled it so that the gas consumption is about 1/2 of the previous amount. I verified this by checking the usage per 10 minutes, before and after, using my gas meter as the measuring instrument. I run the blower 100% most of the heating season to even out temperatures thruout the house as we have a 4-level split level house and the heat rises very well unless you are circulating constantly. My overall gas consumption is very noticeably lower. I have records dating back to 1966 when we bought the house so I can average over several years to see the difference. I'm a cheap SOB, frugal, obsessed with saving money, any or all of the previous appelations.

[Black Dragon]

Costs me around $70. I reside in Western New York.

None. I've had a few instances where they've had emergencies elsewhere and needed to re-schedule but we've always worked it out without hassle.

Those are the same kinds of people who think about vehicle maintenance only when theirs is in the shop having an expensive repair done that could have easily been prevented with a bit of prudence. They deserve the consequences of their actions as far as I'm concerned. As are the nitwits who must sweat or freeze until an expensive repair is done on their broken HVAC systems because they're to cheap too have them properly maintained to begin with.

[clare]

PSC is permanent splic capacitor motor - in other words, a simple induction motor with a run cap. An ECM is an "electrically commutated motor" - basically a permanent magnet DC motor with hall effect sensors and solid state power switching devives instead of brushes - a brushless DC permanent magnet motor.

[clare]

But it can very much AFFECT efficiency. Maximum efficiency is achieved when the burner is running constantly to provide the required heat. Every time a burner stops and starts, efficiency is lost.

An oversized furnace is less efficient than a "right-sized" furnace.

[Vic Smith]

Yes, you have to separate old from modern furnaces/boilers. I cut down gas supply on flame of my old boiler because the designers didn't care about gas prices and half the heat went right up the chimney. There's no question that improved efficiency, as my gas bill dropped considerably, and the basement got cooler from reduced vent heat. Adjusting combustion air was trivial. The only down side was lengthened heating cycles - slower to heat. But that system only ran a small circ pump, so juice was minimal.

Wouldn't think about messing with my 12 year-old furnace, reputedly

+80 efficiency. I would consider economizing the exhaust, because the vent is hot as hell, and there's plenty of waste heat going up the chimney. A well designed and conductive finned vent and a fan would probably extract as much heat as is coming from any of the upstairs vents.

The key indicator to high-effieceny furnaces is the PVC vent. That tells you something right there. It's silly to argue about cutting down on thousands of BTU's going right up the chimney if you can do that safely.

I've seen some talk here about draft inducers improving efficiency. Might for some furnaces if the inducer is always running. But for my furnace that's all bullshit. The inducer on mine only goes on for 60 seconds at startup. If the furnace would start without it a natural draft would be established in seconds, even with bad chimney atmospherics. The only purpose for it I can assume is safety. Ensures you don't have a blocked chimney - but only at start-up. And on mine it doesn't do squat for draft safety after the initial start-up. I just verified that by pulling the tube to the inducer pressure switch after the inducer shut down. The furnace kept right on firing.

Now if there was a blocked vent the rollout sensors would probably shut it down. If that's true they would do the same at start-up without an inducer should there be no draft. So I'm not sold on the necessity of the inducer on my furnace. And I'm totally skeptical that it improves efficiency. I've watched flame conduct many times when I had the motherboard problems with startup. If I ever get ambitious I'll bypass the inducer at startup and watch flame conduct. Maybe block the vent and test the rollout sensors too. Doubt I'll get that ambitious.

Besides, the inducer may be just for those times when atmospherics have the chimney downdrafting at startup time. Highly unusual where I live, but it does happen. HW heater pilot has never blown out in 13 years in this house, but did a couple times in the 15 years at my last house.

Anyway, those are my views as a former Navy boilerman/stationary engineer and almost know-nothing about modern furnaces. I pay attention to the know-nothing part when I fool around with my furnace. Safety first.

--Vic

[.p.jm.]

Bullshit. It GREATLY depends.

For instance - take a 50 year old 'right sized' POS furnace with like 70 % AFUE effective. Compared to an 'over-sized' modern unit at 95 % +. Eh ?

Even with short-cycling, that over-sized furnace may be more efficient than the 'right' one.

[Vic Smith]

I think that's pretty spot on. When I had a pro out to fix mine, he never mentioned getting PM done. I asked about cleaning the evap and he asked if it was cooling good and I said it was. He said it wasn't worth the labor of getting at them and cleaning them, just change the filter frequently. Said to cut the power and hose off the condenser fins every 5 years or so. Of course he was a repairman tech, not a cleaner. I get flyers from "furnace maintenance" outfits with my gas bill but haven't bit yet. Only thing I might do is find the flue design and buy some brushes that will work. Did that on my old boiler and got a lot of crap out of there, but it may have been a converted oil burner. Since I haven't noticed any loss of efficiency in my current furnace, I'm in leave-well-enough-alone mode. But something tells me a flue cleaning would improve efficiency. That's something that can sneak up on you because the change is gradual.

--Vic

[clare]

OK, it's best to compare apples with apples, but the35 year old 75% efficient basic furnace I removed, right sized, would still be as or more efficient than a 95+% furnace of twice the required capacity. My old furnace WAS pretty well optimized, although it was slightly oversized for my house.

20X30 ft 2 storey mid--seventies brick and siding house in south-central ontario - heated exclusively with natural gas - including domestic hot water, for $700 per year. - and virtually no difference when the "old" furnace was replaced with the new high-tech non-condensing furnace escept a siseable difference in the hydro bill.

[clare]

Hey, I never said ir did anything for efficiency - I said BECAUSE the furnace is so efficient, a natural draft may not be created immediately on startup - so the "draft inducer" gets the air movement up the stack started to make sure you get ptoper ventilation. It IS a safety item. Any other advantages would be bonus side-effects.

[Home Guy]

"hr(bob) [e-mail]" unnecessarily full-quoted:

If your furnace has a variable-control gas regulator valve, you could have more easily just turned that to dial-down the amount of gas reaching the burners.

Even if it doesn't have a dial control, I bet there's a valve on the gas line running to the furnace, maybe about 3 to 6 feet away from the furnace, and you could have also partially closed it to reduce the gas flow as well.

[Home Guy]

[e-mail] unnecessarily full-quoted:

If you've extracted so much heat from the combustion process that the exhaust gases are cool, then you have no choice but to force the combustion gases out of the furnace - and out of the house - by using a draft fan because you won't have any natural convection happening in that case.

The draft motor is one of those extra electricity-consuming devices on modern furnaces that are overlooked when comparing the total electricity usage of old vs new furnaces. The proper operating of the draft motor, and the proper operation of the sensors that monitor it, electrical inter-connects, relays, etc, are additional points of failure for the modern furnace that older furnaces simply don't have.

(rest of the unnecessary full double-quote deleted)

[Home Guy]

There's no reason why it can't function as one.

By partially closing off the gascock valve, you're not necessarily reducing the inlet pressure (the pressure beyond the valve going to the regulator).

When the burners are not going, the pressure on both sides of the gascock will be the same. When the burners light up and get going, there might be a slight reduction in the pressure between the gascock and the regulator valve in the furnace.

[Hell Toupee]

Two problems with this source. First, it's the wrong sort of source to support your claim. It is a book about the topic of energy conservation. It is NOT a specialized HVAC manual. It's intended to provide a broad and fairly basic overview of energy conservation, and as such includes chapters on building design, lighting, HVAC, etc. Second, it's woefully out of date, as it was published seventeen years ago. You had to have noticed the page where electronic ignition is described as a "new development in gas heating systems".

It is imprudent, if not highly dangerous, to use as a technical guide an old, outdated book that only touches on gas furnaces in a brief, general, and decidedly non-technical manner.

[clare]

Not if he adjusts the blower speed to give the proper temperature rise across the heat exchanger. Run the fan too fast, and yes, you are correct.

[clare]

Which is an extremely mickey mouse way of doing things. Changing the orifice (jet) sise is the correct way if there is not an adjustable pressure regulator in the system. The ball valve (or whatever) on the

1 inch iron pipe feeding the furnace is a pretty gross adjustment.

[clare]

Any cred you may have built over the last 2 days just went down the crapper, HomeGuy.

With propane at 11 inches water column pressure, a .078" diameter orifice (jet) produces just over 50,000 BTU per hour. For natural gas at the same presuure you are looking at something like a 0.100" orifice.

You are going to effectively regulate that flow with a valve on a 1" iron pipe???

NOT!!!