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Lies, Damned Lies, and Manometer Readings
- aj7 3y agoIf you call an HVAC firm in Tucson, often they simply use the call to try to sell you a brand new unit, making disparaging comments about the condition of the current unit, and outright lying about its fixability.
- jrockway 3y agoI feel like everyone is guilty of something like that. Nobody wants to understand how the existing system works, they just want to rewrite it from scratch ;)
- JesseHVAC 3y agoI would argue that hvac is uniquely bad
- droopyEyelids 3y agoThis is a weird rule of life: if something can be done by an ordinary person, but you hire someone else to do it, be prepared for a huge bill and/or chicanery. Obviously not all HVAC is in the realm of a normal person's abilities, but much of it, and almost all problem diagnosis, only requires reading the diagram inside the furnace, using a multimeter, and a screwdriver or wrench. It's all very trouble-shootable. If you have those basic skills you should be able to identify what exactly is causing the issue, and the tech won't be able to lead you down the garden path.
- readthenotes1 3y agoBefore the pandemic, I had to replace my outside AC unit. I got three different quotes, each of which suggesting three different required changes, from electrical to new duct work. I asked the first quoter about all the other work #2 and #3 suggested and he scoffed at it and said he did not want to keep his guys working in my attic one second longer than necessary in the August heat and that the electrical work was completely unnecessary. Similar to dentistry, they're doing something useful but it's hard to know how much of it is actually valuable
- quercusa 3y agoContractors typically/frequently install AC condensers and furnaces that are too big for the house. These cost more and the contractors don't have to worry about call-backs for insufficient cooling or heat. Unfortunately they are much less efficient because they run for such short cycles.
- a_gnostic 3y agoSo build a walk-in freezer, and run them for that?
- eternityforest 3y agoWould variable speed drives help with this issue at all?
- astrange 3y agoHow about moving everyone to heat pumps?
- quickthrowman 3y agoA heat pump can benefit from a VFD, it has a compressor pump.
- ProllyInfamous 3y agoVSDs, in general, are MUCH MORE efficient than typical 3-phase heat pump.
- mikewarot 3y agoIt took some digging, but I managed to find the specifications for the temperature limit switch in my High Efficiency heating system... for $7.62 I was able to buy a replacement from Grainger, and get it installed. I strongly suspect if I had called for service, I'd be told I needed a new furnace, even though this one is less than a decade old.
- Brian_K_White 3y agoWhere was this limit switch? If it was on the flue, then it's a symptom of a drafting problem when they fail. Basically the thing should rarely ever click, but if the flu isn't drafting well, then the snap disk will get triggered frequently. You'll never notice anything wrong because the heat still works fine. Then the thing fails and you fix it, but you only fixed a symptom and not the problem. Even so, I still think it's better to get in there and figure stuff like that out than to avoid it. "just let the professional do it and do whatever they suggest" only works if you have some way of finding a guy who is both knowledgeable and honest. Yeah there are obviously risks like being unaware of invisible unsuspected things like above, but life is risk regardless.
- wombatpm 3y agoCheck your filters. Some residential units have a mesh between the squirrel Cade fan and the fire box. Mine got partially block by an errant piece if insulation that was restricting air flow and causing the unit to short cycle. I too thought it was a bad switch. The HVAC dude said my condenser coil was clogged and I needed a new unit. One disassembly and cleaning later and it runs like new. When taking things apart take pictures showing where plugs wires and screws go.
- toomuchtodo 3y agoIf it’s the high limit temp switch, that can be triggered by extended furnace runtimes when the temperature is so cold outside that the furnace must run nonstop to keep up with thermal losses (polar vortex and whatnot). This will potentially manifest in smart thermostats as frequent reboots, as the limit switch cuts off power to the furnace (which cuts power to the thermostat) to prevent it from bursting into flames. I can’t speak to Nest thermostats, but ecobee will send you an alert.
- ckemere 3y agoI’d love suggestions for measurement tools to quantitate my home AC units…
- baking 3y agohttps://www.youtube.com/watch?v=eFmDmk1Siqc https://www.youtube.com/watch?v=eFmDmk1Siqc
- JesseHVAC 3y agoI'm the author of the article. The dual manometer suggestion below is excellent. I use external static pressure to calculate airflow using manufacturer tables quite frequently. It's fast and only slightly less accurate than using an expensive flow grid. I also use a manometer to measure pressure drops across filters and AC coils quite a bit. I'd add a tool for measuring temperature, ideally a digital psychrometer, but even something that just measures dry bulb is useful for heating and bad AC failure. Finally a multimeter, ideally with clamp on amp readings.
- Animats 3y agoFew people understand HVAC. Although if you have anything to do with running a data center, you have to learn the basics. I was once in a computer room at Stanford which had two large industrial AC/heat units. I was there to copy old backup tapes (alumni were saving some history) and had a lot of free time while the tapes spun. I noticed that one A/C unit was on heat, and the other was on cool. So they were wasting a vast amount of energy. You're supposed to wire those units together so they cooperate. Their controller can do that. Nobody knew that.
- nick7376182 3y agoYou mean the licensed, bonded, 4-year apprenticed installed and twice inspected system was set up inefficiently? Mild shock!
- deleted 3y ago[deleted]
- wombatpm 3y agoUniversity HVAC systems are weird. We had a steam valve stick open in our building one summer. Brought the internal temperature up to 95. Apparently the chillers bring them temp down to 55F to condense the humidity, then they reheat to 74F. I would not have thought that steam was required for proper AC
- quickthrowman 3y agoSteam isn’t required, electric reheats can manage humidity just fine.
- wombatpm 3y agoIt was the University of Minnesota. They had a big steam plant for heat in the winter
- 3y ago
- benlivengood 3y agoI designed and installed a heat-recovery ventilation system in an Alaska house (new construction). I was aiming for five-star or five-star-plus rating but there was enough leakage that it only got four-star-plus. Still nothing to scoff at compared to the standard contiguous U.S. houses, but the amount of sealing at joints, electrical/plumbing penetrations, HVAC, and vapor barriers was pretty intense. Even the seal under the front door can be enough to lose a rating point if it's bad. Balancing the HRV was done by some professionals once the install was done, and only required a manometer to adjust some wall vents and a baffle in the exhaust duct, which wasn't quite the same as heating/cooling calculations would be, since heating was hydronic and AC isn't really a thing in AK.