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

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On Mon, 13 Dec 2010 21:44:41 -0500, snipped-for-privacy@snyder.on.ca wrote:

    True - and it's STILL a dumb-ass thing to do in a combustion chamber. Can you say 'roll out' ?
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On Mon, 13 Dec 2010 21:53:02 -0500, .p.jm.@see_my_sig_for_address.com wrote:

It would take one heck of a rollout to get the jet hot enough to melt the solder - - -
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On Mon, 13 Dec 2010 17:49:00 -0500, snipped-for-privacy@snyder.on.ca wrote:

There's some kind of misunderstanding here about simple fluid flow and pressure, how gas burns, etc.. I can't get into technical details because I'm not an engineer. But I know....things. As I've mentioned, I cut down the flame on my old boiler by simply moving the gas supply ball cock lever until the flame was where I wanted it, and adjusted air flow to get a good flame. That was a vertical flame - the burner was directly under the boiler water jacket flue passages. So there's no question a gas supply line ball cock - intended as a stop valve - can regulate burner pressure effectively. Understand that the gas company supplies natural gas to residential customers in my area at 1/4 psi. By reducing the volume allowed through the valve I reduced the pressure at the burner orifices, and reduced the BTU per hour burn. In that case I lowered exhaust temps, increased the on-cycle, and came out ahead in terms of efficiency. I wouldn't try that with my current furnace, because it has a horizontal flames reaching into heat exchanger tubes. The nozzles have a good 3-4" of open air between them and the heat exchanger tubes. (BTW, that's a real good reason for an induced draft at startup.) I strongly suspect gas pressure/nozzle size are critical for safe and efficient operation on this one, and shouldn't be trifled with. They were easily manipulated on my old boiler.
So what's this all mean? If Home Guy plans on regulating gas burn on a new furnace, he should at least find one with a vertical flame. I don't know if they make them for forced air furnaces.
--Vic
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Vic Smith wrote:

I guess we can argue if a partially-closed supply valve is acting as a flow restrictor (reducing the quantity per unit time of gas that reaches the furnace) or if it is functioning to reduce the pressure of the gas reaching the furnace.
Obviously if the valve is partially closed, it must function primarily to reduce the quantity flow to the furnace. It could very well be that because of the size of the burner orifices that they are the real bottle-neck to quantity flow, and the pressure on either side of the partially-closed supply valve remains the same at all times.

I have been altering the size or intensity of two (2) furnaces over the past 5 years by turning the variable control dial on the pressure regulator inside these furnaces. This is the same control dial that must be turned (and depressed) to the "Pilot" setting in order to ignite the pilot light, and then turned about 90 degrees to another position to allow full flow to the burners. But instead of turning this dial the full 90 degrees, I turn it maybe 25 degrees to get a "lazy", less intense flame.
A third furnace (which dates to about 1981) is a "whisper heat" unit with electronic ignition (and a motorized combustion-air damper door and resettable over-temperature sensors on various parts of the cabinet). I had to re-solder the ignition transformer on the PC board control module of that furnace 5 years ago (basically when it came under my care and control) because I was observing intermittent ignition. That furnace does not have a pressure control dial like that found in the furnaces with a standing pilot. What I began doing this year is to regulate the flame intensity of that furnace by partially closing it's gas supply valve while observing the flames through the open damper door.
All 3 of these furnaces have long horizontally-placed burners that are positioned at the bottom of the heat-exchanger galley where the flames rise vertically directly from the burners.
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snipped-for-privacy@snyder.on.ca wrote:

I can only say that if you have access to an older-style furnace with easily visible, horizontal burners (not the "in-shot" type) then you can easily see for yourself how manipulating the main supply valve can reliably and consistently alter the size or intensity of the burner's flames.
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    I shudder to ask, but .... what is your excuse for not putting in orifices of the capacity you want instead ? They are cheap, and easy to change.
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Sure, you can "control" the flame, but accuracy and repeatability are not really in your lexicon when you do this. Soldering the "jet" and re-drilling it is a much more "scientific" , repeatable, and accurate way of doing it. (and getting a jet of the same size/format as a permanent replacement is even better) It's not just the size of the jet either - the "format" of the jet - the taper on the inlet side(if any) and or the outlet side, can significantly affect the volume of gas flow through a jet of a given "bore"
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On Mon, 13 Dec 2010 21:50:44 -0500, snipped-for-privacy@snyder.on.ca wrote:

    And it 's total bullshit.

    Thank you. Why not skip the bullshit DIY'r crap and just give the correct answer ?

    And the velocity and pattern of the outlet gas, and the quality of the air / fuel mixture, thus the quality and efficiency of the flame. So why not just do it right ?
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snipped-for-privacy@snyder.on.ca wrote:

Accuracy is not called for here.
Anyone dialing-down the gas supply to the burners will not know ahead of time what the exact precise flow rate should be that they are intending to achieve. Much the same way that you won't initially know what setting your barbeque's controls or gas stove need to be in order to get a certain temperature on the grill.
In this excercise, you dial the gas down, you let several hours (or days) pass, you note how the duty cycle of your furnace has changed, and you either leave it alone or you adjust it up or down as needed.

And also more effort for no real, effective gain in terms of the desired end result.
If the furnace has a variable dial on it's gas valve/regulator, then use it. If it doesn't, try the main shut-off valve.
Yes, you know that changing the jets by getting smaller ones (or making them smaller with solder) will give you a smaller flame and less BTU's. But you really don't know by how much until after they're in place. And if the new jets are too small or not small enough, then you've got to partially dis-assemble your burners and change the jets.
Makes about as much sense as saying that replacing the potentiometer in my stereo's volume control with fixed resistors is a better way to control the intensity of sound coming from my speakers. Does it matter if the fixed resistor is "more accurate" ?
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Your stereo doesn't need a specific fuel/air mix to operate the way it was designed to. FWIW, I have *NEVER* seen a furnace gas valve with a "variable dial" on it.
Oh, and while I am at it, HomeBoy.... you sure that your name isn't really Homer Simpson??
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Steve followed poor usenet message-construction style by unnecessarily full-quoting:

We already discussed adjusting the primary combustion-air baffle plates, which are most likey already in the incorrect (lean) wide-open position in your average open-burner, standing-pilot furnace anyways, making your observation somewhat irrelavent, but still easily remedied.

Here ya go:
http://www.air-n-water.com/photos/2090-m.jpg
Now, do you want some help pulling your feet out of your mouth?
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That is *NOT* a variable dial.... it strictly turns the gas valve on or off.... it is *NOT* variable.
Now do you want to pull your head out of your ass??
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Steve wrote:

You are on drugs. See that blue dial? That's a variable-position dial. You get more or less gas going to the burners depending on it's position. Try it some time.
What is wrong with you people anyways?
You want to so hard to believe that it's not possible to dial-down the BTU output of old furnaces.
I don't know what your problem is.
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wrote:

They make em steve. They have a sensor that goes in the supply air and you set the valve according to the supply temp that you want. Usually see them on direct fired make up air units. Seen them on Reznor gas fired duct heaters too.
The King is dead but not forgotten.
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On 12/14/2010 3:53 AM, ftwhd wrote:

Ya. Much as I hate to agree with ftwhd, I worked on a Marv-Air make up air unit yesterday that had a variable gas valve.
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The only "variable" adjustment I have seen is the manifold pressure adjustment.... but then I don't do commercial or industrial stuff as a rule.
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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.
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wrote:

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.
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wrote:

I wonder how much the cold air that is still flowing through the old furnace cools the air down in winter while it's moving through it 24/7? I would never circulate air constantly in winter as I believe with losses through the ducts, furnace, etc, its a losing proposition. However, at least with a new furnace with draft inducer, the air moving throguh the combustion chamber when its off will be way less.
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On Sat, 11 Dec 2010 20:35:08 -0800 (PST), "hr(bob) snipped-for-privacy@att.net"

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