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

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.

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.

----------------------------------------- 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:

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

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.

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

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:

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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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.

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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Here in the south, thats not an issue... the problem here is finding a small enough furnace with a big enough blower drive to support the A/C. As a rule, I install furnaces that are 2 stage with a variable speed blower... especially with dual fuel/hybrid systems, and its a very rare occassion when the second stage of the furnace kicks in.

Are you serious?

The King is dead but not forgotten.

--Vic

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

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

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)

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.

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.

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.