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Burner air intake adjustment and flame color, flame length and combustion flow

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Burner air intake adjustment and flame color, flame length and combustion flow HVAC Guy 10-31-2007
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Posted by Zyp on October 31, 2007, 10:13 pm
HVAC Guy wrote:
> ftwhd1 wrote:
>
>> Oh theres your original post... :)
>>
>> I must say for an hvac guy you dont seem very well educated on
>> combustion.
>
> It's just a handle I made up for this thread. Don't focus on it.
> Focus on the questions.
>
>> It would seem that in order for you to fully understand
>> what is goiung on you need to start with the basics.
>
> I'm asking direct questions here regarding the effects of setting the
> air baffles either fully open or fully closed and historically were
> they set fully open for reasons other than correct combustion or best
> efficiency.
>
> I now have 2 possible reasons why in years past the default of
> fully-open may have been routinely used:
>
> 1) prevent chimney condensation by keeping combustion flow high
> resulting in higher flue and chimney temps
>
> 2) keep combustion flow high to create enough passive exhaust flow to
> overcome possible air imbalances that might lead to flue back-flow in
> a well-sealed house.
>
> Both situations sacrifice efficiency in favor of either safety or a
> reduction in future chimney maintainence, and at the time (20, 30
> years ago) both seemed rational based on the price of NG and the
> relatively low efficiencies of the furnaces at the time.
>
>> Learn terms like excess, primary and secondary air,
>
> I could do that, but that wouldn't answer my questions regarding what
> was done by techs in the field, working on actual furnaces.
>
>> The questions you are asking are indicative of a lack of
>> knowledge
>
> They are indicative of a lack of being an hvac tech and experiencing
> first-hand what was actually done by techs 20 or 30 years ago as they
> serviced and adjusted low to mid-efficiency furnaces or even what a
> tech would do today when servicing or adjusting a 20, 30 or even 40
> year old furnace.

HVAC Guy;

Both of those reasons are not "reasons" to set the burner shutter all the
way open. It is likely the furance was never adjusted properly in the first
place. It is likely that many a plumber or furance repair person cared
either. They opened it all the way knowing that was probably safest.

BTW: during the 1970's to 1978 we only had one furance efficiency. After
1979, intermittent pilots came about in an effort to conserve on fuel. By
1981, induced draft and slimer heat exchanger's came. By 1988 pilotless
ignition known as Hot Surface Ignition started appearing. Today we have a
host of choices for furnaces depending on what the homeowner / client want's
to pay. Highend, variable speed 96% AFUE furnaces are expensive and not
many homeowners are willing to flip the bill for one of these. Fossil fuel
burning furnaces now can be combined with Heat Pumps to offer a better way
to save fuel and money.

If you would like to learn more, why don't you take a class at your local
Community College? Or possible seek information through your utility
company [the one suppling your fuel].

--
Zyp



Posted by wingnut on October 31, 2007, 11:46 pm
ftwhd1 wrote:
>
>
>>The burners of older natural gas furnaces usually have a round plate
>>that can be rotated to either open or closed positions, allowing a
>>variable amount of combustion air to enter the burner along with the
>>gas.
>>
>>If the plate is fully open, the resulting flames seem shorter, faster,
>>uniform height, and uniform color (blue).
>>
>>If the plate is fully closed, the flames are longer, slower, variable
>>height, and more red in color.
>>
>>It seems that usually the plates are rotated fully open.
>>
>>Is it true that back when natural gas was cheap, these intake plates
>>are usually set fully open to create a faster-moving combustion flow
>>to help increase exhaust temperatures that would help to prevent
>>chimney condensation, and that by closing the plates you are
>>increasing the efficiency of the furnace by slowing the combustion
>>flow and allowing more of the heat to be transfered to the heat
>>exchanger instead of escaping out the flue?
>
>
> Oh theres your original post... :)
>
> I must say for an hvac guy you dont seem very well educated on
> combustion. It would seem that in order for you to fully understand
> what is goiung on you need to start with the basics. Like the
> combustion triangle and progress from there.
>
> Learn terms like excess, primary and secondary air, what they are,
> where they come from and the effects on combustion. Learn about fuel
> to air ratios . I suggest looking up Backarack <sp> on the web. They
> have some good info on combustion in the training room.
>
> The questions you are asking are indicative of a lack of knowledge
> which is fine but beyond the scope of this NG imo. Have you
> considered formal training on the subject?
>
>

You may be too hard on him. This type of equipment may be rare in his
area. I know it is in mine.
Heat strips or heatpumps is about it here, if there is heat at all.







Posted by ftwhd@home.com on November 1, 2007, 4:56 pm
wrote:

>ftwhd1 wrote:
>>
>>
>>>The burners of older natural gas furnaces usually have a round plate
>>>that can be rotated to either open or closed positions, allowing a
>>>variable amount of combustion air to enter the burner along with the
>>>gas.
>>>
>>>If the plate is fully open, the resulting flames seem shorter, faster,
>>>uniform height, and uniform color (blue).
>>>
>>>If the plate is fully closed, the flames are longer, slower, variable
>>>height, and more red in color.
>>>
>>>It seems that usually the plates are rotated fully open.
>>>
>>>Is it true that back when natural gas was cheap, these intake plates
>>>are usually set fully open to create a faster-moving combustion flow
>>>to help increase exhaust temperatures that would help to prevent
>>>chimney condensation, and that by closing the plates you are
>>>increasing the efficiency of the furnace by slowing the combustion
>>>flow and allowing more of the heat to be transfered to the heat
>>>exchanger instead of escaping out the flue?
>>
>>
>> Oh theres your original post... :)
>>
>> I must say for an hvac guy you dont seem very well educated on
>> combustion. It would seem that in order for you to fully understand
>> what is goiung on you need to start with the basics. Like the
>> combustion triangle and progress from there.
>>
>> Learn terms like excess, primary and secondary air, what they are,
>> where they come from and the effects on combustion. Learn about fuel
>> to air ratios . I suggest looking up Backarack <sp> on the web. They
>> have some good info on combustion in the training room.
>>
>> The questions you are asking are indicative of a lack of knowledge
>> which is fine but beyond the scope of this NG imo. Have you
>> considered formal training on the subject?
>>
>>
>
>You may be too hard on him. This type of equipment may be rare in his
>area. I know it is in mine.
>Heat strips or heatpumps is about it here, if there is heat at all.
>
>
I wasnt trying to be hard on him. Now that I know he is just another
homeowner Im pretty much done with him. If he wanted to have a
reasonable disscussion about combustion then he needs to learn the
lingo which he unwilling to do.

Posted by -zero on October 31, 2007, 10:48 pm

>
> The burners of older natural gas furnaces usually have a round plate
> that can be rotated to either open or closed positions, allowing a
> variable amount of combustion air to enter the burner along with the
> gas.
>
> If the plate is fully open, the resulting flames seem shorter, faster,
> uniform height, and uniform color (blue).
>
> If the plate is fully closed, the flames are longer, slower, variable
> height, and more red in color.
>
> It seems that usually the plates are rotated fully open.
>
> Is it true that back when natural gas was cheap, these intake plates
> are usually set fully open to create a faster-moving combustion flow
> to help increase exhaust temperatures that would help to prevent
> chimney condensation, and that by closing the plates you are
> increasing the efficiency of the furnace by slowing the combustion
> flow and allowing more of the heat to be transfered to the heat
> exchanger instead of escaping out the flue?


No.

-zero





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