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Heating

3 tools, 5 guides, 3 comparisons

Furnaces, heat pumps and the efficiency ratings that price them — AFUE, HSPF2 and the cold-climate question.

Thermal-toned gas furnace with a glowing heat exchanger
The heat exchanger glowing inside a cool cabinet: input on one side, output on the other.

Tools

Furnace Size Calculator

Heating

Input BTU/h and output capacity from load, climate zone and AFUE.

BTU/h · AFUE

Heat Pump Sizing Calculator

Heating

Capacity at design temperature, balance point and the supplemental-heat gap.

BTU/h · balance point

AFUE Fuel Cost Calculator

Heating

Annual heating cost from AFUE, fuel price and load — gas against electric.

$/yr · AFUE

Federal minimums

Minimum efficiency by heating product class
Product classMinimumCitation
Non-weatherized gas furnace80% AFUE10 CFR 430.32(e)(1)(ii)(A)
Non-weatherized gas furnace, from 2028-12-1895% AFUE10 CFR 430.32(e)(1)(iii)(A)
Non-weatherized oil-fired furnace83% AFUE10 CFR 430.32(e)(1)(ii)(C)
Weatherized gas furnace81% AFUE10 CFR 430.32(e)(1)(ii)(E)
Electric furnace78% AFUE10 CFR 430.32(e)(1)(ii)(G)
Split-system heat pump7.5 HSPF210 CFR 430.32(c)(5)(ii)
Single-package heat pump6.7 HSPF210 CFR 430.32(c)(5)(iv)

Sources: 10 CFR 430.32(e)(1)(iii) (read 2026-09-04)

Guides

How to Size a Furnace

Heating

From heating load to nameplate input, with the derating steps for altitude.

9 min read

AFUE Rating Explained

Heating

What annual fuel utilization efficiency measures, and the federal minimums.

8 min read

Furnace Troubleshooting

Heating

Blowing cold, short cycling, no ignition — a decision list, question by question.

11 min read

Cold Climate Heat Pumps

Heating

Capacity at 5°F, balance points, and when a dual-fuel setup wins.

11 min read

HSPF2 Explained

Heating

The 2023 metric, how it differs from HSPF, and the COP behind it.

8 min read

Comparisons

Heat Pump vs Furnace

Compare

Running cost, install cost and capacity at design temperature, side by side.

HSPF2 vs AFUE

Gas vs Electric Furnace

Compare

Fuel cost per delivered BTU, install cost and lifespan.

$/MMBtu

Two-Stage vs Single-Stage Furnace

Compare

Comfort, cycling and the price gap that decides it.

stages · CFM

Other sections

Sizing & Load

Manual J load, BTU/h, tonnage, duct sizing and static pressure — the numbers that decide what equipment goes in.

5 tools · 4 guides

Cooling

Air conditioners, mini splits, refrigerant and SEER2 — the cool side of the manifold.

3 tools · 5 guides

Service & Costs

Replacement cost, maintenance, filters and the credits that move the price — what the job costs and what keeps it running.

4 tools · 5 guides