Dwyer Magnehelic Gauge to measure draft

If you can't find one or they're too expensive, go here:

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l2632&_nkw=draft+gauge&_sacat=42909

I use this for over fire draft. The analyzer records draft in the flue. It also does velocity for airflow tests in ductwork. 

Yes, you turn the zeroing screw. It's not uncommon to have to do that especially on the low-pressure gauges. The #460 however will never lie to you. Not as convenient because you have to use fluid, but nothing ever goes wrong with them. Most of the Dwyer's you have to use Dwyer's colored fluid which does have a different specific gravity than water and the manometer is calibrated for that fluid, so you have to use it. That being said the Magnehelics are pretty rugged.

Oh, i see, the 460 is a flow meter, i thought it was a manometer. the 460 is what you want I think.

@MikeAmann

This is what I used to use. We used to have a ton of those at the shop. Weil McLain used to ship them out with commercial boilers so the service tech could measure overfire and breeching pressure. In fact, Weil McLain had their name put on them. We got them for free because the pipefitters installing the boilers didn't know what they were for so they would give them to us. You could use them as a straight manometer for gas pressure up to 16"wc or as an inclined manometer to read draft and breeching.

I used them on the Trane roof top units that had a negative pressure gas burner

https://tab.dwyer-inst.com/products/test-equipment/manometer/portable/series1227.html

You could make your own with a piece of tubing. Laying out an inclined scale could be a bit tricky and I think you need the inclined scale for the precision you need for draft if your fluid is water. That was what I did when I wanted to measure the gas main pressure. Problem was I wanted it worst case so I did it when it was around 0 f and the water froze by the time I got it torn down.

This one is my favorite, but they are discontinued. They are big, sturdy, and accurate. You can find these Bacharach MZF gauges on ebay with some careful shopping, sometimes as part of the Bacharach combustion wet kit. Bacharach also makes a pocket draft gauge but that of course can't be permanently installed like the MZF can.




This one isn't marked, but the negative side is to the right of zero if you were wondering. The needle swings around zero depending on how the gauge is leveled, but just place it on top of any flat surface and move the adjustment lever on the right side.

As far as electronic gauges, I don't trust them as far as I can throw them. I've spent a career in electronics including design and just don't trust the long term accuracy of transducers.