EcoRenovator - View Single Post - Homemade u-tube manometer

abogart · 02-08-12, 07:18 AM

Got it full of blue water, zeroed up, taped to the return duct, and tubes run to the return and supply.

Here's the whole setup. Kinda looks like an educated redneck put this together, hehe...

Reading with the t-stat set to FAN. Low speed fan operation.

Reading during a heating cycle. High speed fan operation. I noticed that it didn't quite return to zero after shutting the fan off the first time, so I removed the zip tie at the bottom of the 'U' and pulled the whole loop out a bit to zero it back up.

I wasn't quite sure how to properly read it. According to this Wikipedia article, "The difference in fluid height in a liquid column manometer is proportional to the pressure difference." Since I labelled the scale at 1" increments, the value read on the bottom tube needs to be doubled to account for the lowered height of the upper tube. Since this read about .2" WC on high, my total external static pressure is .4" WC.

I now realize that I could have increased the accuracy of this thing by decreasing the incline of the tubes and only having the scale read 1" either side of zero. That would give it the ability to read up to 2" WC with more accuracy in the range that I'm using it for. I just might make another base plate for it with a shallower incline when I get some free time. I have some tubing left over and I want to make a vertical u-tube with a larger scale for reading things like gas manifold pressure.

At least now I know what's going on inside the ducts, and I have a working gauge to keep an eye on it.

EDIT: It just dawned on me that I should have put the low side in the blower compartment downstream of the filter. That way I should be able to tell by looking at the gauge when the filter is restricting airflow.

02-08-12, 07:18 AM	#5
abogart Efficiency Afficionado Join Date: Jan 2012 Location: Michigan, US Posts: 68 Thanks: 21 Thanked 6 Times in 4 Posts	Got it full of blue water, zeroed up, taped to the return duct, and tubes run to the return and supply. Here's the whole setup. Kinda looks like an educated redneck put this together, hehe... Reading with the t-stat set to FAN. Low speed fan operation. Reading during a heating cycle. High speed fan operation. I noticed that it didn't quite return to zero after shutting the fan off the first time, so I removed the zip tie at the bottom of the 'U' and pulled the whole loop out a bit to zero it back up. I wasn't quite sure how to properly read it. According to this Wikipedia article, "The difference in fluid height in a liquid column manometer is proportional to the pressure difference." Since I labelled the scale at 1" increments, the value read on the bottom tube needs to be doubled to account for the lowered height of the upper tube. Since this read about .2" WC on high, my total external static pressure is .4" WC. I now realize that I could have increased the accuracy of this thing by decreasing the incline of the tubes and only having the scale read 1" either side of zero. That would give it the ability to read up to 2" WC with more accuracy in the range that I'm using it for. I just might make another base plate for it with a shallower incline when I get some free time. I have some tubing left over and I want to make a vertical u-tube with a larger scale for reading things like gas manifold pressure. At least now I know what's going on inside the ducts, and I have a working gauge to keep an eye on it. EDIT: It just dawned on me that I should have put the low side in the blower compartment downstream of the filter. That way I should be able to tell by looking at the gauge when the filter is restricting airflow. Last edited by abogart; 02-08-12 at 07:24 AM..