furnace too big

[oilie hands]

is there any way to make a furnace work right in a house if it is about 50,000 BTUs oversized?-- need some more professional opinions for a homeowner.

[Gunnery Sergeant Hartman]

Tear it out and install the correct size.

[drcustom]

Put an addition on...

[t527ed]

leave the windows open

[rimek]

MORE as in number or in quality of opinions?
This is a loaded post- Who has determined the oversized condition? What, if it is so, is the correct size relationship(in other words, is 50K a 50% oversizing or a 25% oversizing or what?) Why is the unit oversized? Why isn't the first thought to replace with the correct size, will there be expansion in building? If this is a new install, why not get the installer by the short ones, and get satisfaction? If these factors don't concern you, then just load that sucker up-open all the windows, punch holes in the roof, etc.

[oilie hands]

well, a 90000 would suit his needs perfectly. He bought this and installed it. thought bigger was better,I went there to see why it was recycling all the time, burner shutting off and then the blower running for about 6 min, then off, then on and so on until the exchanger cooled, I just told him that the unit was grossly oversized for his needs. He would have to pipe hot air to the outside and cold air in side to equalize the thing, they don't believe me. this unit would easly heat 2 houses like theirs.

[casturbo]

Is this an oil furnace by chance? If so, downfire the nozzle size and run the blower on low speed. You could even adjust the fan and limit settings to accomodate less cycling. Don't go to low on nozzle size or consumption will likely skyrocket and exhaust temps will be too low.

[oilie hands]

yes oil burner, i slowed the fan and set the limits to 90 and 130, from 120 and 150.. I did suggest changing nozzels from 1.00-80B to 85-80B.They also need more- larger ducts, hot and cold. it's just hard to get it through to them.

[tinner73]

Originally posted by oilie hands
yes oil burner, i slowed the fan and set the limits to 90 and 130, from 120 and 150.. I did suggest changing nozzels from 1.00-80B to 85-80B.They also need more- larger ducts, hot and cold. it's just hard to get it through to them.

tell them what it needs and walk away. you don't need the headache.

[beenthere]

Down fire it to .75, and adjust the blower to the middle of the units rated temp rise.

Other then that, they screwed themselves.

[GradyWhite244]

Be careful in downsizing the nozzle. Don't drop below the minimum for the installed end cone if it is a Beckett burner.

[beenthere]

Originally posted by GradyWhite244
Be careful in downsizing the nozzle. Don't drop below the minimum for the installed end cone if it is a Beckett burner.

Hate when I forget those details.

Thanks Grady.

[casturbo]

Originally posted by oilie hands
.... i slowed the fan and set the limits to 90 and 130, from 120 and 150..

I would have reset the limits to 100, 170, 200 instead. With these settings you'll have 70° of limit span which will reduce fan cycling. Brief rundown of each setting has 170° being the fan turn-on temp, 200° being the max plenum temperature (burner high limit) and 100° being the blowdown temperature after the thermostat is satisfied. I usually use these settings on all units, including new installations, since HO (including myself) hate short fan cycling.

[lonnirat]

Lets go back to plan A... Do a heat calc, rip it out, and install a correctly sized unit.

[oilie hands]

UPDATE, first I have to say this, some people can not trot out and buy a new furnace, car or whatever everytime a serviceman or mechanic tells the to, sometimes spending a couple hundred trying to fix something suits their wallet better than spending a couple grand plus buying new.
Here's what i done and they should get a good many safe years out of their unit.
I took out the 1.00-80 and replaced it with an .85-80 and had the option of going down to .70. I took out a cold air return duct that they had in the basement 10 feet from the unit, patched the hole and ran a hot air duct to an unheated entrance room away from the furnace.
I told them to keep the door that leads down to the basement closed, they left it open to relieve some of the heat from their big unit, now the basement is a nice 60 degrees.
CO2 11%-unchanged
draft .025 from .050
stack 420 from over 600
have the fan limit on at 160 and off at 100
heat rise is a little high --about 90 should be 85 or under.
efficiency about 83%
cost to heat for the next yr--unknown.

[casturbo]

When you changed the nozzle to a smaller size, you did adjust the amount of air, right?

The other thing found strange, to me at least, was the draft decreasing when the smaller nozzle was used. Are you checking the draft when the burner is running at the breach?

[oilie hands]

yes, draft is .025 at the box and at the flue.
air was 0, now is open about 3/16"
there is enough draft to suck your hat off, it's an 8' flue going into an 8X12 chimney, should be a six inch flue for the smaller nozzel

[Edited by oilie hands on 03-26-2005 at 01:23 AM]

[casturbo]

Originally posted by oilie hands
air was 0, now is open about 3/16"

That makes it sound like you opened the air, from zero to 3/16".....probably the other way around if you installed a smaller nozzle. You should be using the side disk to adjust air on the Beckett burner as well, not the larger band. Small firing rates should use the disk for adjustment, it promotes better burning (says Beckett anyways).

Originally posted by oilie hands
....there is enough draft to suck your hat off, it's an 8' flue going into an 8X12 chimney, should be a six inch flue for the smaller nozzel

Chimney size doesn't have to be sized to the firing rate, that's what the draft regulator is there for. Open that while the burner is running steady-state to obtain -0.02" WC over the flame. More draft never hurts, but cuts efficiency.....too little draft and the fire suffers and can even burn the end cone Becketts are known for.



[Edited by oilie hands on 03-26-2005 at 01:23 AM] [/B][/QUOTE]

[GradyWhite244]

Originally posted by casturbo

The other thing found strange, to me at least, was the draft decreasing when the smaller nozzle was used. Are you checking the draft when the burner is running at the breach?

I noticed that too but then when I saw the drop in stack temperature, I realized less heat up the chimney = less draft. I don't remember seeing any smoke or CO numbers. Often when you reduce nozzle size, CO goes way up. Not trying to be picky, just cautious.

[oilie hands]

it pays to be questioned and picky when playing with fire.. thanks
heat rise is about 80
CO2-11 CO-6
my old eyes and glasses saw between 0 and 1 smoke
younger eyes said 0, i didn't argue.

[Edited by oilie hands on 03-26-2005 at 11:53 AM]