How to size an air conditioner
Why 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
The per-zone square-feet-per-ton bands, and where they break down.
8 min read
How to size ducts
CFM per ton, friction rate, and the duct calculator method step by step.
10 min read
Static pressure explained
What 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
From heating load to nameplate input, with the derating steps for altitude.
9 min read
AFUE rating explained
What annual fuel utilization efficiency measures, and the federal minimums.
8 min read
Furnace troubleshooting
Blowing cold, short cycling, no ignition — a decision list, question by question.
11 min read
Cold climate heat pumps
Capacity at 5°F, balance points, and when a dual-fuel setup wins.
11 min read
HSPF2 explained
The 2023 metric, how it differs from HSPF, and the COP behind it.
8 min read
Cooling
5 guides
SEER2 explained
What changed in 2023, how SEER converts to SEER2, and the regional minimums.
9 min read
AC not cooling
Running but not cold, frozen coil, compressor silent — a decision list.
12 min read
How often to change your filter
Intervals by filter depth and MERV, and which way the arrow points.
7 min read
HVAC zoning systems
Dampers, bypass, and why a zoned system needs a variable-speed blower.
10 min read
The R-454B refrigerant transition
What the 2025 A2L changeover means for repairs, charging and parts.
9 min read
Service & Costs
6 guides
HVAC replacement cost
What a full system costs installed in 2026, and which line items move it.
11 min read
Furnace replacement cost
Cost by AFUE, stage count and venting, plus the permit and liner line items.
10 min read
AC replacement cost
Condenser, coil and line-set costs, and when a coil-only swap is legal.
10 min read
HVAC maintenance guide
What a real tune-up includes, how often, and the readings worth keeping.
11 min read
HVAC tax credits in 2026
25C, the heat-pump caps, and what the 2025 law changed about the deadline.
9 min read
EPA 608 certification
The four types, the 25-question sections, the 70% pass mark and the 2024 HFC rule.
11 min read