forced air furnace blower high or low?

I've got a gas forced air furnace, installed 1998, a cheapo, SEER 10 (12?), I think. When it was installed, the first year, the blower was set to "low", and it seemed like i wasn't getting enough flow through the vents on the second floor (they run in the attic, and blow down). A new HVAC guy came in the next year to look at it, and switched (actually I think he jumpered it on a circuit board) to blow "high". then he went into the attic, and discovered that someone had left one of the ducts with an OPEN end on it, so I was blowing heat into the attic instead of into the house. He sealed that duct and left the blower on "high".
now I'm thinking this year that maybe the furnace is short cycling. I get blower on times of about 7 minutes, and blower off times of about 8 minutes. I can hear the burner is on for about a minute before the blower comes on, and it's off for another 2 at the end of the cycle, so I've got flames about 5 of the 7 minutes that the furnace is on.
2 questions in particular: should I call someone in to reset the fan/blower down to "low" again? (is this something I could reset myself? I'm smart, I'm handy, I work on computers for a living...)
How come this furnace, when I set the thermostat to have the fan ON all the time, will have the fan turn off at the end of the heat cycle and kick on, then kick off when another heat cycle starts, etc. on and off, on and off, on and off. Is something not set right? I used to have a furnace where when I set the fan on, it stayed ON, no matter if it was heating or not...
I seem to be using a lot more natural gas this year, and since gas costs are up better than 40% around here, I'd like to see what all I can do about optimizing the heat cycles.
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barb gee wrote:

keep the plenum at 150 F. The energy imparted to the system when the furnace is on is delivered at a constant rate. It is independent of the blower speed. It's cu ft/min of gas, gallons/hr of oil, etc converted to heat. But, if the plenum runs at too high a temperature its life will be shortened. Further, it's better from a comfort standpoint to deliver the thermal energy to the living space on as constant as possible a basis. Changing the blower speed is nothing more than changing or moving a jumper. Get a copy of the furnace manual, many are available on the manufacturer's web site as pdf files now.

It has been colder this year in most places that heat a lot.
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The thermostat anticipator should be adjusted for a longer cycle.
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The higher fan speed should not be a problem except for the higher noise level. If you lower your fan speed too much, then your energy efficiency will also drop, since you will not extract heat from the heat exchanger as efficiently.
The burner-fan delays are also part of the energy efficiency. There's no use turning on the fan when the heat exchanger is still warming up, and after the burner goes off, the fan runs to extract the heat still left in the heat exchanger.
As for the fan being interrupted by the burner startup and shutdown when the controls are set to fan on. I have no explanation, but mine does the same thing.

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Ron Kihara wrote:

I HATE that. It's noisy, and it just seems like a stupid way to manage a blower and motor.
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The problem I have with that, is with a dusty (bird dander) environment, it smells like the first time the heat is fired up in the fall, every time the burner kicks on.
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