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:
Using a proper sized jet is the RIGHT way to do it - but what he did works and is often done to determine what the right jet size is.
It would take one heck of a rollout to get the jet hot enough to melt the solder - - -
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??
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.
That's true. But with the induced draft they can safely operate at high efficiency because they can better control how much air goes up the stack.
Last summer we changed out an "old style" gas furnace with an induced draft unit. Tremendous difference in gas usage.
Because we have also switched over to nearly 100% CFL for lighting, we have saved so much electricity that we just don't notice the extra 80 watts used for the draft blower.
But I agree with your main point: the old style motors in gas furnaces do waste quite a bit of power. But the main power hog is the air circulation motor. That can easily cost $.05/hour. That may not seem like much but if that blower operates 24/7, it adds up to over $30/month. A good reason to keep the fan on "auto" rather than "on."
You furnace should be sized so that it can keep you comfortable on a very cold day by operating continuously. You can pick your own numbers but your furnace shouldn't be expected to operate 24/7 more than a day or two each year. That's an extra $1 or 2 or so.
Maybe the next generation of furnaces will also take account motor efficiency. Right now the 90 (plus) % efficiency systems are much, much more expensive than the 80% (the condensation feature adds to the complexity and cost). But like so many other things, prices will come down with competition. It may end up being less expensive to buy a high efficiency HVAC system than to "super insulate!"
As the Idjit who filled in the orifice and then redrilled it, I can assure everyone that I did calculations on what size orifice I needed to get a certain BTU flow. I did this 20+ years ago and don't remember the details any longer, but it was not strictly based on cross-section of the orifice opening, but also included the effects of friction of the gas with the orifice walls.
If the flame ever gets close to the orifice opening, there will be major problems as at least in my furnace, the actual flame is several inches into the furnace from where the orifice is located. The is an air-mixing tube that goes between the orifice and the burner, and that is where you adjust the airflow to match the gas flow. It may not meet some PhD type of analysis, but it cut down the gas consumption and we stay warm on -10 degree nights and days so I guess I did something right.
As the Idjit who filled in the orifice and then redrilled it, I can assure everyone that I did calculations on what size orifice I needed to get a certain BTU flow. I did this 20+ years ago and don't remember the details any longer, but it was not strictly based on cross-section of the orifice opening, but also included the effects of friction of the gas with the orifice walls.
If the flame ever gets close to the orifice opening, there will be major problems as at least in my furnace, the actual flame is several inches into the furnace from where the orifice is located. The is an air-mixing tube that goes between the orifice and the burner, and that is where you adjust the airflow to match the gas flow. It may not meet some PhD type of analysis, but it cut down the gas consumption and we stay warm on -10 degree nights and days so I guess I did something right.
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Your still alive, thats a plus.
----------------------------------------- Yep! I understand your frustration. I have to drag my cold bum out into the worse than freezing weather to change them out and often on a package unit where it is ALL outdoors. Here is the facts though... There are many less deaths today caused by asphyxiation due to lack of draft or cracked exchanger and fire from burner failure. I think the whole "efficiency" statement is marketing and is more likely for increased revenue and new production markets for the economy. Whatever the reasoning, if it has saved one single life it is worth it. When yours failed it might have even saved yours or that of your loved ones.
------------------------------------- J.P. Avanti Services HVAC, Steam and closed loop Hydronic heating. In the service field for 25 years.
On the roof. Where there is no place to safely secure a ladder. In a blizzard / ice storm. In the dark. Late at night. When everyone else in the county followed the emergency advice on the radio and went home early. Except the store owner who called. Who told you when you got there that she wants to lock up and leave right away, and you should stay by yourself until it's fixed. With no other living being within a half mile if you need help, like if your ladder blows down, or you slip on the 2 ''s of new ice everywhere. Because she's late getting dinner on the table. And by the way, you do give 30 days billing for new customers you never heard of before who found you in the Yellow Pages that night ?
Oh, the memories .....
Most likely the unit was originally greatly oversized or grossly inefficient for your tinkering to have worked so effectively.
MOST 30 year old and older units were grossly oversized.
It's not the unit was oversized, the unit was oversized for the particular size house or heating application.
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?
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 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.
They really aren't more expensive at all TODAY. With a 95% furnace you get a 30% Fed tax credit. That's 30% off the price to begin with. Then I get $400 from the gas company and another $400 from the state clean energy program. Add all that together and the 95% furnace is a no brainer compared to
80%
What else did you think I meant? Pretty obviouse it is "oversized for the application" because if the same furnace was installed in an arena it would be grossly undersized.
The tendancy was to go with "bigger is better"
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 days2 - 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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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.
I would think for the installer, erring on the side of being say 20% too big is more of an issue of playing it safe. Worst case, the furnace runs a little less and is a little less efficient, something the homeowner will never bitch about. If theyt make the mistake of putting in one that's too small, then the customer is going to be screaming because the house won't maintain temperature on the coldest days. And that's a difficult problem to fix.
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