Attic blower times.

tmtruett

Hello I have a oil boiler and forced air. 2 handlers one in basement and one in attic,

My question is the blower cycling time of attic unit. When heat is first called it runs for over 3 minutes. When temp reached I have timed it to be a pattern of approx 2 and half minutes off and only 40-45 seconds on. Not sure if I am over thinking this but thought I'd ask any veterans out there if that is "normal". Took pic of the stat setting and model if at all helpful. Thanks

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EBEBRATT-Ed

I would suggest that your heat anticipator setting or cycles per hour setting in the thermostat is incorrect

HVACNUT

Can you explain the 3 minutes run, two and a half minutes off, 40-45 seconds on thing in more detail?

With that setup, the strap on aquastat is set to bring the fan on once water temperature reaches 140°. I'm not familiar with that control. Check the cover to see if there's an adjustable or fixed differential.

As an example, the fan comes on at 140°. Say the aquastat differential is 20°. It should be mounted on the return side of the coil. If the fan throws off so much heat it drops the return temperature to 120°, the fan will turn off until return temperature reaches 140° again. When the thermostat satisfies, the fan will continue to run until until the return temperature reaches 120°. That's where the anticipator @EBEBRATT-Ed mentioned comes into play.

tmtruett

Hello. sorry I was not getting email notification

So when heat is first called for, say turn it up from 60 to 65, it will run for an 3-4 minutes, off for 2 or so minutes and repeat until temp reached. Once reached it will run for only 45 seconds and then stay off for 2 1/2 -3 minutes and repeat. That run time seems short to me. In the pic, I removed the cover of the aquastat to check wiring connections. Not sure it is set correctly, it is adjustable

mattmia2

What kind of thermostat? You have to figure out which control is shutting it down. That cycle rate sounds a lot like a mechanical thermostat with the cycle length set way too short.

mattmia2

If it were a limit control or aquastat the cycle length probably wouldn't vay much with a 5 degree difference in room temp but the anticipator on a thermostat would.