triple D

Are you 100% sure that thare is not a timer on or near furnace? It would have a small time clock on it, and some brown wires. One of wich would go to a damper in this intake. If not, than you are correct in plugging it off for now, but it should be corrected in spring. And by the way, a gas furnace starts flowing through registers immidietley when the thermostat kicks, but the fire will not start for around 30 to 45 seconds after. Then it will take another 5 minutes at least before heat at registers is at full running temp. Did you turn on the furnace and go check the temp, then go close damper and check again while still running the same cycle? This could explain some of the temp. increase in your test you performed. None the less, if there is no damper, the installers of that one screwed up. If there is a sticker on that furnace, dont call them for repairs. Good luck again...

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Richwho

Nope, there's no timer or damper. To install this they simply closed off a floor joist until they reached an exterior wall, then they drilled through the exterior wall and put the diffuser vent in so it feeds into the cold air return space (joist). So if want damper control I'll have to tear that out and run 6" duct work to allow me to put in a damper.

I waited until the furnace had been running for a full fifteen minutes to take my two temperatures, so everything was up to temperature. But in my experience the forced air furnaces I've been around don't behave as you describe. Everyone I've ever been around the burner kicks on first and when the lower limit of temperature is reached the fan then kicks on. When the thermostat stops calling for heat the burner shuts off and the fan runs until the temperature drops to the lower limit again. I've never encountered a furnace where the blower starts before the burner.

Hube

A quote byTriple D said; "And by the way, a gas furnace starts flowing through registers immidietley when the thermostat kicks, but the fire will not start for around 30 to 45 seconds after."
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huh!.....you say....." a gas furnace starts flowing though the registers"........
I don't think so....(lol) some furnaces are pretty big to ever come thru the registers.

Note; The burner will be activated when the T stat calls for heat, but the main blower should not come on for perhaps 2 or 3 minutes after the burner ignites. This gives the air within the furnaces' heat exchanger a chance to get warm enough before sending it out to the supply registers.