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

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On Sun, 12 Dec 2010 16:57:08 -0600, The Daring Dufas

Yes - EVERYONE just KNEW you could not run a gasoline reciprocating engine lean of peak without burning valves. It was generally accepted "proven fact" until "Lindy" showed them otherwise.
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On 12/12/2010 10:20 PM, snipped-for-privacy@snyder.on.ca wrote:

It was OK for him to fly until he started shooting down Japanese Zeros.
TDD
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On Sun, 12 Dec 2010 17:16:07 -0500, snipped-for-privacy@snyder.on.ca wrote:

Natural gas flame is easy to adjust, as you've outlined. But sometimes gas pressure and gas quality changes. Seems the "quality" part is usually temporary. Might even be just pressure changed and not quality at all. But I can imagine gas pressure changing permanently, though I haven't really noticed it. The gas stoves I've had have been harder to adjust than any furnace, and they're also where you'll commonly notice changes in the gas supply quality or pressure. I have to look at the kitchen range. One burner won't light. Tomorrow. Or Thursday.
--Vic
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On 12/12/2010 5:38 PM, Vic Smith wrote:

Like just about anything, the conventional NG furnace is setup for a generic set of variables by the manufacturer. Like a vehicle with a carburetor, a skilled tuner can get hold of it and make it run better. Most service manuals outline adjustments for furnaces but most service personnel never bother with a tuneup and leave it factory set. :-)
TDD
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Home Guy wrote:

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.
--
Black Dragon

QOTD:
"It's a cold bowl of chili, when love don't work out."
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aemeijers wrote:

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.
--
Black Dragon

Being frustrated is disagreeable, but the real
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wrote:

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
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.p.jm.@see_my_sig_for_address.com wrote:

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.
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There I fixed it for you.
The King is dead but not forgotten.
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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
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On Sun, 12 Dec 2010 16:41:53 -0600, Vic Smith

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.

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snipped-for-privacy@snyder.on.ca 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)
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I'll bet the energy used by that small draft inducer and the electronics is so small that it's small compared to the savings in fuel that you get in going from 80% to 95%. I mean we can make electronics so that things like a GPS or cell phone can run off small batteries for long periods. What makes you think furnace electronics need to use so much electricity?
Also odd you choose that small motor that's only on during firing to focus on, yet you're a big fan of a pilot light in old furnaces that burns 24/7, including summer when the furnace isn't on.
I know, you turn your pilot light out in summer. I do too, but I'll bet 90% of people don't.
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I agree with the concept that a furnace will be more efficient if the temperature differential across the heat exchanger is less. How much it changes, ie if you screw around with an old 75% efficient furnace and turn the burners down, will it raise the efficiency from 75 to 76, or 75 to 80, however is an important part. You are assuming it's substantial. I'm not so sure.
But the problem here aside from the obvious practical problems of doing it, is that you can't undo it on the fly. If you can turn the burners down so that it fires at 70% for greater efficiency, then one of two things must exist:
1 - The furnace will now be unable to heat the house to normal temp on the coldest days
2 - The furnace was oversized all those years and you now have downsized it permanently.
Those modern two stage or variable burner furnaces can change the firing % on the fly. Using it at 100% when the intelligent thermostat knows it's needed, or firing it at say 70%, when it's a mild day.
Another thing strikes me here. You keep pointing out how you can buy cheap HVAC online and you apparently believe you could do installs yourself or pay someone on the cheap to do part of it for you. With the current incentives, ie Fed 30% credit, nat gas utility credit, electric credit, state credit, I can get $3,000 off the cost of a new system. That means doing it your way, you could have a whole new high efficiency 95% furnace and AC system for $1000. Don't you think that's a good value proposition, with a good payback period?
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I agree with the concept that a furnace will be more efficient if the temperature differential across the heat exchanger is less. How much it changes, ie if you screw around with an old 75% efficient furnace and turn the burners down, will it raise the efficiency from 75 to 76, or 75 to 80, however is an important part. You are assuming it's substantial. I'm not so sure.
But the problem here aside from the obvious practical problems of doing it, is that you can't undo it on the fly. If you can turn the burners down so that it fires at 70% for greater efficiency, then one of two things must exist:
1 - The furnace will now be unable to heat the house to normal temp on the coldest days
2 - The furnace was oversized all those years and you now have downsized it permanently.
Those modern two stage or variable burner furnaces can change the firing % on the fly. Using it at 100% when the intelligent thermostat knows it's needed, or firing it at say 70%, when it's a mild day.
Another thing strikes me here. You keep pointing out how you can buy cheap HVAC online and you apparently believe you could do installs yourself or pay someone on the cheap to do part of it for you. With the current incentives, ie Fed 30% credit, nat gas utility credit, electric credit, state credit, I can get $3,000 off the cost of a new system. That means doing it your way, you could have a whole new high efficiency 95% furnace and AC system for $1000. Don't you think that's a good value proposition, with a good payback period?
______________________________
He doesn't care about payback on a new system, because he isn't going to buy one from a competent, licensed, insured, professionally trained, HVAC contractor. He just wants to get the cheapest POS, and have it "checked" by a hack that will work for beer money. Then he will have something to else to bitch about when the system routinely fails in the first year, and has no warranty. He doesn't care about the energy savings or the comfort of a correctly sized, and properly installed system.
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On Thu, 16 Dec 2010 09:02:59 -0800 (PST), snipped-for-privacy@optonline.net wrote:

Are you serious?
The King is dead but not forgotten.
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http://www.youtube.com/watch?v
uDDqU6n4o
--Vic
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snipped-for-privacy@optonline.net wrote:

Based on where I've turned the regulator dial on my home furnace, and by judging the resulting flame height, I think I'm easily running at about 1/2 the full-throttle fuel flow. My furnace is a lennox g8-120-1, manufactured October 1976. Specs:
0 - 2500 ft altitude: 120,000 btu input 96,000 bonnet BTU orifice size 39 temp rise 70 - 100 1/4 hp motor (?) 3 1/4 inch pulley
The furnace is about 22" wide, 28" deep, and about 4.5 ft high. AC coils mounted in plenum above the furnace.
I changed the pulley to 4" a few years ago to get more airflow (higher fan RPM). Interesting that it says it's supposed to have 1/4 hp motor. The higher altitude spec says 1/3 hp, and higher static pressure (.75 vs .2 inches WC). I am at a lower altitude (850 ft above sea level).
We've had a few nights now where the over-night temp has gone down to 10F, daytime high 15F, and my furnace is still cycling (not 100% duty cycle). I have the thermostat set for 71F (electronic thermostat, not mechanical, 2 degrees hysteresis). I haven't started my humidifier (I don't always run it in the winter). Current indoor humidity is 20%. Today's low and high temp is 13F / 22F.
Bottom line is that it's amazing how much you can turn down the burners and still keep the house at the desired temperature, even given these low outside temps.

?
Turning the control knob on the regulator is pretty-much on the fly. If you mean that my thermostat can't do it, well I don't think that's necessary. For the next 3 months I'm looking at a pretty constant outdoor climate in terms of temperature, so constant regulation of the furnace burner output is not necessary.

I don't know what's normal for a 2000 sq foot (including basement) 2-story house, brick sided first floor, aluminum sided second story (no insulation under the siding) in terms of furnace BTU. My climate zone is basically Detroit / Cleveland / Buffalo / Toronto.
I think that the HVAC industry was probably targeting a 25% furnace duty cycle back in the mid-1970's, so a 120k BTU furnace was spec'd back then for a house like this.

I really don't think that a fully controllable / variable burner is necessary or is cost efficient for the average home. Two stage - maybe. Two stage aftermarket electronic thermostats are insanely priced compared to single stage. I bought a 2-stage programmable thermostat for a leased office about 10 years ago (to replace a mechanical thermostat) and I think it cost $300 at the time, compared to $50 - $70 for a single-stage "home" version.

I would install it myself, because I belong to the school of "it's not done right unless you do it yourself", and there's a lot of stuff I do for myself (car restoration, welding, plumbing, wood-working, concrete work, etc).

A new furnace might cost me $1500 max to buy, a 30% rebate of that is max $450.
It's not the money that would motivate me one way or another. What would really cut my energy bills is putting a 2" layer foam-board insulation around my second-story and getting new windows. I'll let everyone else pay through the nose for new furnaces so that they will use less natural gas resulting in a continued depression for natural gas prices which will mean that people with inefficient furnaces will continue to pay less anyways.

I've got several other home-projects in mind for the next few years. When I'm ready to alter my air-handling system to include the concepts I've talked about here, that's when I'll take a good look at my furnace and decide if I'll buy a new one (I probably will). But I'll still install it myself, and if that means I'll have to buy it on the internet because the local hvac dealers won't sell it to me unless they install it, then so be it.
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Which unfortunately says nothing about whether the furnace is more efficient at the lower firing rate or by how much. However if you can fire it at that reduced rate and keep the house at the desired temp on the coldest days it does say the furnace was oversized to begin with.
Any differences in furnace efficiency in heating at full firing rate versus 70% would be so small that you'd have to have instrumentation to figure it out. Note that HVAC and manufacturing folks claims for two stage "efficiency" are really based on:
less cycling of the furnace, so less heat loss when it shuts down, etc
more even heat distribution, due to the blower running longer, possibly resulting in feeling more comfortable at a slightly lower tem.

So, essentially you have it throttled back in Fall and Spring and on full during winter. That's part of what a two stage furnace would do. Difference is that with a two stage furnace and thermostat, if you're out of the house in Oct and set it back to 60, it will fire at the higher rate. Even the 2 stage without a 2 stage thermostat will start at low, then move to high after an adjustable period, eg 5-12mins.

25% cycles when? on the coldest days? From all you've said, sounds like it's oversized.

I can buy a top of the line Honeywell VisionPro 2 stage Tstat for $100-125. Or a cheaper prgrammable one for $60. The delta for getting two stages on a good thermostat is maybe $25

Are there no gas company or state rebates/credits available? Here in NJ there are and they would chop another $600 off that price. From what I've seen posted here, there frequently are similar credits available in other states. That could make the cost of that new furnace $450.

Hard to see how you would not recover the cost in a reasonable time of getting a furnace that is:
A - Sized correctly B - 95% efficient compared to your current whatever, say 75%
Using your own numbers, ie $1500 cost, Fed Tax credit, no other rebates, it's $1050. IF you only cut your fuel costs by $200 a year, that's a fast payback. With any other rebates/credits it could be down to a few years.

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snipped-for-privacy@optonline.net wrote:

Given a lower BTU output and a slower flame speed (slower combustion air induction speed) I am promoting more heat residency time inside the heat exchanger galley and a lower flue stack temperature. My blower fan is pushing the same CFM through the exchanger, so when taken together my heat extraction efficiency is going up. By how much, I don't know.

Isin't it common knowledge that oversized furnaces were normal a few decades ago?

Actually, it's throttled back right now, to at least half of full flow. That's my point - even given my current outdoor climate (10 to 15f min and 20 to 25f max outdoor temp) I'm getting enough BTU's to keep the house at 71 - 72F all day and all night. And even then, my furnace is not running at 100% duty cycle. Maybe only 65 - 75%.
To be honest, the burner setting I have now is the lowest that gives me a consistent and even flame pattern and acceptible ignition roll-out.
Fall and spring don't last long enough to warrant their own lower burner-output setting, which as I just mentioned I probably couldn't achieve anyways.

Yup.
Tell me what a 120,000 BTU input, 96,000 btu bonnet furnace is designed for. What size house.
Tell me where such a furnace ranks today in terms of size (small, medium, large, extra-large, etc).

First thing, I'm in Ontario (Canada).
Second thing, in order to get gov't rebates, you need to contract for a home efficienty test by an acredited tester who will evaluate your current situation (air leakage, current furnace type and efficiency, maybe a few other things) and he will do it again when your new furnace is installed, and then he signs off on the tests and then the gov't will send you money. I don't know if it's "federal" or "state" money (or both). I also don't know if the local gas utility will kick in any of their own money.
One of my co-workers had this done, so I'll ask him how much of a kick-back he's supposed to get.
You've also got to factor in rebates for the heating vs the cooling components as well. I wouldn't be interested in replacing my A/C system.
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