I recently had a complaint from someone staying at my house that the guest room stayed too warm when the door was closed. Knowing there was no air return vent in that room, I figured the door being closed was preventing good air flow. But, sadly, there was no good way to test this (with the tools I had). So, I went hunting on eBay for the proper tools, and found the TSI DP-Calc 8705 (a Micro-manometer) with no bids, for $15! Sure, it was listed as broken, but they admitted they just didn’t have the means/knowledge to test it. And the sticker had shown it was calibrated in 2012. So, I bought it. Even if it was broken, it would probably be a decent source of parts, or a good teardown to send to the EEVblog. =)
Unit arrived a couple weeks later, and was in amazing condition. Sure, it didn’t come with the RS-232 cable, or tubing, or static/pilot tubes, but I didn’t really need any of that for my purpose. It seems to register perfect, and I was able to go around my house and measure the pressure differentials with the door closed (sticking the more positive “sensor” tube under the door from the main part of the house into the room with the HVAC running). With that, I got the following results:
Bedroom 5.72 pascals (high)
Son’s room: 9.2 pascals (very high)
Bathroom: .747 pascals (great!)
Office: 3.48 pascals (high)
Now, it seems Florida may be the only state that has ratified/codified standards for closed door pressure differentials at 2.5 pascals (0.01″wc), but using those numbers, it does seem like the gap under all my doors (except possibly the bathroom) is too small. I say possibly with the bathroom because excess pressure would just push out the bathroom fan exhaust. So my next quest will be to cut the door openings a bit larger and see how that changes things.
I also made a nice serial interface cable for the unit using an old DB-9 cable, and some RJ-45 ends. To figure out the pinout, I emailed TSI, and they sent me the whole schematic for the unit! The pinout is “backward” from right to left looking at an RJ-45 connector, but making the cable was pretty painless, and seems to work. The unit literally sends the measurement to the computer when you hit “Print” (just plain old ASCII). If you type “V” on the computer, it’ll echo back the current reading. Pretty simple, and could make for some fun experiments.
Overall, while the unit is pretty old relative to more modern units, it still does an amazing job, and is more than capable of doing what I need.