lowering output of furnace?


I have several rooms in my house that I don't have to use, so I close them off and shut off the heater registers in those rooms to save energy. However, this causes the remaining registers to become very windy and noisy. I believe the reduction in air flow also increases the furnace output temperature and therefore increases heat loss while the air is traveling in the heating ducts in the crawlspace. Also air is lost due to leakages in the heating ducts -- my crawlspace is warmer than outside by at least 10 degrees.
Is it generally possible to lower the heat output of a furnace? This is what I have (replaced last year):
http://216.122.22.11/FetchDocument.aspx?ID/062936-65bd-456d-9783-559b84978136
I see three burners inside. I can either pull out one of the burner, or use the shut-off valve to reduce the gas supply. I imagine removing one burner would be more efficient since the remaining two burners will operate at their designed setting.
But I'm not so sure the blower speed can be change. I don't mind rewiring anything if I know it can be done.
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in my opinion this is a very bad idea for too many safety reasons. if you think you can economically and safely re-engineer the furnace better than they already designed it for its 80% efficiency, i believe you may be dangerously incorrect. it would make more sense to safely replace the furnace again with a highest efficiency model with the variable speed blower and whatever other options you desire. you will want to do a payback analysis on your upgrade costs versus the energy savings. easier things to do instead: i would use insulation everywhere it may be installed and zone thermostat controls for your ducts. and, be sure your piped drinking water flow in winter does not require this crawl space heat. consult your hvac installer to explore any options of blower speeds that may exist in the present furnace, and discuss heat anticipator settings of zone thermostats.
peter wrote:

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Then you should have gotten a 2 stage furnace and a variable speed blower. For what you have consider insulating the ducts in the crawlspace. Or just move to a smaller house or remove part of the house. Sounds like your house is too big for your needs.
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I have a friend who went too big on his furnace:( A HVAC contractor can downsize the output by elminating burners but he said it coist him some efficency, at home resale time you will need to change it back.
probably better to upgrade homes insulaion!
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"I have several rooms in my house that I don't have to use, so I close them off and shut off the heater registers in those rooms to save energy. However, this causes the remaining registers to become very windy and noisy. I believe the reduction in air flow also increases the furnace output temperature and therefore increases heat loss while the air is traveling in the heating ducts in the crawlspace. Also air is lost due to leakages in the heating ducts -- my crawlspace is warmer than outside by at least 10 degrees.
Is it generally possible to lower the heat output of a furnace? This is what I have (replaced last year): "
Even if you could turn off part of the burner, how is that going to solve a problem of the remaining registers being windy and noisey? That is determined by the blower, not the temp of the air coming out. If anything, it will only make it worse, because with reduced heat output, the blower will run even longer.
And if you have leakages in the crawlspace, it would seem the solution to that would be to fix them, not lower the output of the furnace.
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Leaks in the crawlspace may be a good thing, if you live in cold climate area it may be the only thing keeping your pipes from freezing down there on one of those real cold winter days.
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peter wrote:

You could change pulleys on blower/motor, but it'd probably be simpler to identify the registers that are, in effect, whistles and replace them. Assuming that you're not trying to force too much flow through them- too much fan/too few register sq-ft.
Like, if your system had x registers with, say 20 ft/sec flow through them, and you now have x/3 of the same registers, you'd have wind tunnels. You don't want to radically reduce the discharge area, and maybe want to consult with local experts.
One thing that might help right now, is to lower the fan-switch setting on the furnace, so the fan comes on at lower temp. (And shuts off at lower temp also.) This will reduce temp of ducting, obviously, and boost efficiency of unit.
Some registers I've seen tend to whistle when almost closed. You may want to open some up a bit. Or replace with quieter.
J
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Closing off rooms totally is not a good idea. You may be able to reduce the heat that is let into the room but don't cut it off totally. The exterior walls, ceiling and floor will get extra cold without the heat, humidity produced in the house will still find its way into the rooms and condense on the cold surfaces. This can cause moisture damage and moulds to grow on the surfaces and inside the framing.

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it is not recommended to do this as it may cause condensation in the unit. any heat/ac unit is designed for a certain air flow and btu rating. reducing the air flow could also cause the unit to cycle on it's high limit control which could cause much worse such as a cracked heat exchanger.
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If you're willing to screw around with the furnace, you ought to be willing to modify the ductwork. If the furnace isn't short-cycling because you're not moving enough air to keep it cooled down, AND if the noise you're hearing is being generated at the grilles, you might be able to reduce the noise just by stepping up a size and using bigger grilles. Otherwise, Add more duct and registers to the rooms you ARE using, to make up for the amount of air that you're no longer moving through the closed rooms.
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