How to Size an AC Unit
Sizing & LoadWhy square-foot rules of thumb oversize, and what to measure instead.
9 min read
HVAC guides
Written for people who put the equipment in and the people paying for it. Every figure carries the source it came from and the date it was read.
Sizing & Load
4 guides
HVAC Tonnage per Square Foot
Sizing & LoadThe per-zone square-feet-per-ton bands, and where they break down.
8 min read
How to Size Ducts
Sizing & LoadCFM per ton, friction rate, and the duct calculator method step by step.
10 min read
Static Pressure Explained
Sizing & LoadWhat total external static pressure is, how to read it, and what a high number costs.
9 min read
Heating
5 guides
How to Size a Furnace
HeatingFrom heating load to nameplate input, with the derating steps for altitude.
9 min read
AFUE Rating Explained
HeatingWhat annual fuel utilization efficiency measures, and the federal minimums.
8 min read
Furnace Troubleshooting
HeatingBlowing cold, short cycling, no ignition — a decision list, question by question.
11 min read
Cold Climate Heat Pumps
HeatingCapacity at 5°F, balance points, and when a dual-fuel setup wins.
11 min read
HSPF2 Explained
HeatingThe 2023 metric, how it differs from HSPF, and the COP behind it.
8 min read
Cooling
5 guides
SEER2 Explained
CoolingWhat changed in 2023, how SEER converts to SEER2, and the regional minimums.
9 min read
AC Not Cooling
CoolingRunning but not cold, frozen coil, compressor silent — a decision list.
12 min read
How Often to Change Your Filter
CoolingIntervals by filter depth and MERV, and which way the arrow points.
7 min read
HVAC Zoning Systems
CoolingDampers, bypass, and why a zoned system needs a variable-speed blower.
10 min read
The R-454B Refrigerant Transition
CoolingWhat the 2025 A2L changeover means for repairs, charging and parts.
9 min read
Service & Costs
5 guides
HVAC Replacement Cost
Service & CostsWhat a full system costs installed in 2026, and which line items move it.
11 min read
Furnace Replacement Cost
Service & CostsCost by AFUE, stage count and venting, plus the permit and liner line items.
10 min read
AC Replacement Cost
Service & CostsCondenser, coil and line-set costs, and when a coil-only swap is legal.
10 min read
HVAC Maintenance Guide
Service & CostsWhat a real tune-up includes, how often, and the readings worth keeping.
11 min read
HVAC Tax Credits in 2026
Service & Costs25C, the heat-pump caps, and what the 2025 law changed about the deadline.
9 min read