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Originally Posted by hvacrmedic

I was responding to the last sentence in your previous post, which you wrote in the form of a conclusion to the entire preceding argument. The argument was correct, the conclusion wasn't. I apologize for not clarifying.

no problem, many times i forget to form my responses in a way that answers both the OP, the guy im commenting to and to all the other readers.

40 years ago in english class, the public schools never covered " internet forum" composition

Originally Posted by ebierley

This furnace and its manual make easy to dial in the gas pressure. First you need to check static pressure to verify airflow then you can use the chart that is either in the install manual or the service manual which you can get at goodmanmfg.com. The chart gives you the temp rise +- 2degree for each airflow. You adjust the gas pressure to get the rise. As long as you are between 1.8 -2.2 and 3.2-3.8 you are good to go.

eric

Hmmm, no. That isn't what the manual says.

Originally Posted by ch4man

i wasnt speakin of two stage furnaces. only comenting on heat tranfer from fire to chamber to air in response to the OP's question.

i know and agree that low fire usually has a greater o2 content.

excess air ( and therefore o2 ) tends to cool the fire.

i still stand by my statement that a greater temperature difference, the greater heat transfer you have. just ask any wet-head about radiant panel temp....

I was responding to the last sentence in your previous post, which you wrote in the form of a conclusion to the entire preceding argument. The argument was correct, the conclusion wasn't. I apologize for not clarifying.

Originally Posted by beenthere

The heat exchanger diameter, and the flue pipe diameter are size for second stage volume. So an inducer slowing to 66% of its full RPM will be moving more then 65% of the air it does in second stage. Hard to size an inducer to be able to handle max flue pipe length, and still slow down enough for first stage on on short flue pipe runs.

I have found that by installing the restrictor in the intake improves combustion quite a bit. The manual says to install the restrictor on vent that is 10' or less, on all 40k furnaces some 100k that meet the right vent conditions and TO IMPROVE COMBUSTION. I wish the manufacture would give us real combustion numbers to work with, it would be a lot simpler for all of us.

Originally Posted by BigBacardi

been there, you stated earlier that in a 2 stage furnace the inducer doesnt slow down enuf????? and to much excess air.....am curious, cause all 2 stage furnaces have 2 stage inducer motors, wouldnt the mfg install correct motor cfm for each stage?



or a imissing the obvious????

The heat exchanger diameter, and the flue pipe diameter are size for second stage volume. So an inducer slowing to 66% of its full RPM will be moving more then 65% of the air it does in second stage. Hard to size an inducer to be able to handle max flue pipe length, and still slow down enough for first stage on on short flue pipe runs.

been there, you stated earlier that in a 2 stage furnace the inducer doesnt slow down enuf????? and to much excess air.....am curious, cause all 2 stage furnaces have 2 stage inducer motors, wouldnt the mfg install correct motor cfm for each stage?



or a imissing the obvious????

Originally Posted by ebierley

This furnace and its manual make easy to dial in the gas pressure. First you need to check static pressure to verify airflow then you can use the chart that is either in the install manual or the service manual which you can get at goodmanmfg.com. The chart gives you the temp rise +- 2degree for each airflow. You adjust the gas pressure to get the rise. As long as you are between 1.8 -2.2 and 3.2-3.8 you are good to go. Not that confirming by CA is a bad thing.

eric

So if you follow the manual your good to go and if you follow the manual and check w/ CA and your oxygen is 12% at least you checked? I used to do it the same way before I bought my CA and knowing what I know now I wouldn't set up or check a furnace any other way.

This furnace and its manual make easy to dial in the gas pressure. First you need to check static pressure to verify airflow then you can use the chart that is either in the install manual or the service manual which you can get at goodmanmfg.com. The chart gives you the temp rise +- 2degree for each airflow. You adjust the gas pressure to get the rise. As long as you are between 1.8 -2.2 and 3.2-3.8 you are good to go. Not that confirming by CA is a bad thing.

eric

i wasnt speakin of two stage furnaces. only comenting on heat tranfer from fire to chamber to air in response to the OP's question.

i know and agree that low fire usually has a greater o2 content.

excess air ( and therefore o2 ) tends to cool the fire.

i still stand by my staement that a greater temperature difference, the greater heat transfer you have. just ask any wethead about radient panel temp....

Originally Posted by ch4man

now your getting it, many of us have been speaking of heat-exchanger efficency. remember hot air heats the house, heat exchangers heat the air, and the fire( proper combustion, this is the only portion a combustion anayizer measures) heats the heat-exchanger.

so physics state there is greater heat transfer when there is a greater temperature differential. therfore a more efficient furnace has a hotter fire

That's incorrect. Energy efficiency and heat transfer efficiency are two entirely different things. If by a feat of engineering prowess a furnace is designed and set up so as to keep the stack temp and excess air constant when switching from low to high fire, then the combustion efficiency will be exactly the same in low and high fire. This is the whole point of O2 trim controls, and in most cases with O2 trim the combustion efficiency will be higher in low fire than in high fire, flame temperature notwithstanding.

I do have to say that the company I used to work for on the north shore of Chicago had what I thought was a good way to size his equipment. He would size at 0 degrees. When I asked him why he did that instead of the standard -5 to -10, he asked me how often are we at -5. I thought for a Min. And said well I guess for a couple of weeks or so. He replayed, so for 2 weeks of the year the furnace will run full boar. The rest of the time it will run more efficantly than if we increased the size. ( we were installing Trane 20k BTU increments on size). For the 9 years I was with them I had 2 systems that the customer insisted that we up the size. We did what they wanted at no extra caust.

Originally Posted by SBKold

Warm air coming from vents for longer time rather than hot air for 15mins then off back on ......off.....

Temp rise in high vs. low doesn't typically vary by more than 5° on a properly commissioned furnace. There is less air moving in low stage though so runtime is extended vs. high stage.

Originally Posted by MicahWes

Wait, are you speaking of the IR radiation from the flame itself to the inside walls of the HX as opposed to the heat transfer from the HX to the airstream of the house?

now your getting it, many of us have been speaking of heat-exchanger efficency. remember hot air heats the house, heat exchangers heat the air, and the fire( proper combustion, this is the only portion a combustion anayizer measures) heats the heat-exchanger.

so physics state there is greater heat transfer when there is a greater temperature differential. therfore a more efficient furnace has a hotter fire

Originally Posted by MicahWes

Wait, are you speaking of the IR radiation from the flame itself to the inside walls of the HX as opposed to the heat transfer from the HX to the airstream of the house?

Now your catching on. Under fired your not getting the heat from the IR of the flame to the HE walls like you should.

I don't know how much design temp weather you have had since you installed the furance but I'd like to know how cold it actually has to get before the 2nd stage kicks in. I have a feeling a LOT of 2 stage furances are getting installed where the 2nd stage is never needed. A Smaller 1 stage furance could do the job for a lower cost while maintaining the same comfort. Sadly 2 burner furnaces are rarely installed as the primary heat source for a single family home, regardless of heating needs.

Wait, are you speaking of the IR radiation from the flame itself to the inside walls of the HX as opposed to the heat transfer from the HX to the airstream of the house?

Wait, IR (as in infared radiation) is responsible for 1/2 BTU output? It has been a long time since my thermodynamics classes in college, so there is a lot I may be mistaken about, but isn't most heat transfer in a warm air furnace via conduction and convection?

I think I understand now, first stage is for comfort. Thanks for the input. I guess u learn something new every day.

Originally Posted by MicahWes

WHY is 1st stage less efficient???

Because the inducer does not slow at the same proportion as the reduction in gas.It will slow down but not directly proportional. You then have even more nitrogen entering the combustion chamber causing a cooler flame and less heat tranfer. IR heat transfer is over half of the BTU output so yes a reduction is a big thing.

Okay that makes sense. I find myself experiencing the draft issue when I'm watching tv. And I see the point of the inducer not slowing down to match fire rate making it a little less efficant than a variable speed inducer or a modulating inducer. However I would still contest that first stage is more efficant than 2nd. I guess the best way for me to explame myself is that, in first stage we are consuming less gas and getting less btu's. If I can maintain temp and consume less isn't that more efficant. I think of it like a heat pump. It's more efficant to run compressor till the load is to great / balance point. At wich time it is more efficant to turn the strips on. So I would think it would be better to run first stage for as long as possible. I can see how full fire is more efficant on a high load because it would satisfy the stat a lot quicker and use less gas doing so. But I can only see that situation commng about for only a couple of weeks throughout the heating season assuming the home is properly insulated.