▸ Field notes
Plain-English HVAC,
from the jobsite.
Definitions, diagnostic logic, and the trade context that gets skipped in the rush to sell you a unit. We add entries as we have time to do them justice.
TXV Explained: The Thermostatic Expansion Valve and What It Does
A thermostatic expansion valve meters how much liquid refrigerant enters the evaporator. Get it wrong — stuck, hunting, miscalibrated — and the whole system runs hot, cold, or just plain bad. Here's how to read one.
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SEER vs SEER2: What Changed in 2023 (and Why It Matters)
SEER got replaced by SEER2 in 2023 — new test protocol, new minimums, new tax-credit thresholds. Same machine, just measured more honestly. Here's what changed and how to read a spec sheet without getting tricked.
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MERV Ratings: What Filter Numbers Actually Mean
MERV is a 1-to-20 scale that tells you what size particles a filter can catch. Higher isn't automatically better — go too high in the wrong system and you strangle the airflow. Here's what each band actually does.
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BTU, Explained: What One British Thermal Unit Actually Does
A British Thermal Unit is the amount of energy it takes to heat one pound of water by one degree Fahrenheit. That tiny definition is the foundation underneath almost every HVAC capacity number you'll ever read.
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The HVAC Field Glossary
A running, plain-English reference for the terms, codes, and acronyms that come up daily on the jobsite. Definitions, why they matter, and the things people consistently get wrong.
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