Showing Posts From
Hvac
Commercial HVAC Tons per Square Foot (Sizing Guide)
Commercial HVAC sizing by square feet per ton, with planning figures for offices, retail, restaurants, warehouses, and server rooms — why internal gains dominate and why a block load calc is required.
Duct Size Chart: How to Match Duct Size to CFM
A round duct size chart by CFM, what a ductulator actually does, the friction-rate and velocity rules behind it, how to convert round to rectangular, and how to size supply vs return ducts.
Furnace and AC Replacement Cost (Replacing Both Together)
What it costs to replace a furnace and air conditioner together: combined price ranges by efficiency tier, why a matched system is worth it, the cost breakdown, and when to replace just one.
Heat Load & Cooling Load Calculation: How It Works
How an HVAC load calculation works — the heat-loss formula Q = U × A × ΔT, the sensible and latent parts of a cooling load, a worked residential example, and how to convert load to tonnage.
Will a Higher SEER Save You Money? The Real Math
How much a higher-SEER air conditioner actually saves on your bill, the formula linking SEER to annual cost, a cost-by-rating comparison, and the payback math that decides whether the upgrade is worth it.
HVAC Labor Rate: How to Set Your Hourly Rate
How HVAC contractors set a billable labor rate that actually makes money — the loaded-rate formula, labor burden, overhead, billable-hour reality, flat-rate vs T&M, and a worked example.
How Much Does a New HVAC System Cost in 2026?
Installed cost ranges for central AC, furnaces, heat pumps, and full systems in 2026 by size, efficiency tier, and region. What drives the price up or down, plus tax credits.
Return Air Duct Sizing: How to Size the Return Side
How to size return air ducts: why returns must match supply airflow, a return duct size chart by CFM, single vs multiple returns, filter grille sizing, and the static-pressure problems undersizing causes.
What Size Mini Split Do I Need? (Sizing Chart)
How to size a ductless mini split: a BTU-by-room-size chart, single-zone vs multi-zone sizing, why oversizing wrecks an inverter, and the adjustments that change the number.
Essential HVAC Formulas Every Tech Should Know
The core HVAC formulas in one place: sensible and latent heat, total heat, CFM, tonnage, delta T, static pressure, SEER/EER, and the constants behind them, with worked examples.
How Much Does Furnace Replacement Cost? (2026)
What a new furnace costs to install: price by size, fuel type, and AFUE efficiency, the factors that move the total, repair vs replace, and how to estimate your job.
How Much Does It Cost to Run Central AC?
What central air costs to run per hour, day, and month. The formula tying tonnage, SEER2, and electricity rates to your bill, plus worked examples and ways to cut cooling costs.
EER vs SEER vs SEER2: What Each Rating Means
EER, SEER, and SEER2 all measure AC efficiency differently. What each one means, how they're calculated, how to convert between them, and what counts as a good rating.
How Much Does Central Air Installation Cost? (2026)
What it costs to install or replace central air conditioning: price by tonnage and SEER2, the factors that move the total, install vs replacement, and how to estimate your job.
Dew Point and HVAC: Why It Matters in Duct Design
What dew point is, why ducts sweat and grow mold when surfaces drop below it, the comfort thresholds that feel muggy, and how insulation and vapor barriers prevent condensation.
How to Estimate an HVAC Job: A Contractor's Pricing Guide
A step-by-step way to estimate and price HVAC jobs: counting true job costs, applying the right markup/margin, building an accurate quote, and avoiding the estimating mistakes that kill profit.
What Is Manual J? Heat & Cooling Load Calculation Explained
Manual J is the ACCA standard for calculating a home's heating and cooling load. What it is, the inputs it uses, how heat load and cooling load are calculated, and why it beats rules of thumb.
How Much Does Ductwork Replacement Cost? (2026 Pricing)
What new or replacement ductwork costs — by the foot, by the run, and for a whole house. The factors that move the price, repair vs full replacement, and how to estimate your job.
How to Size a Dehumidifier for Your Home
How to size a dehumidifier by square footage and dampness level, what the 2019 DOE pint rating change means, and when to choose a whole-house unit over a portable.
BTU per Square Foot for Air Conditioning: The Chart and the Math
How many BTU per square foot you need for cooling, with a room-size chart, the climate adjustments that change the number, and why 20 BTU/sq ft is only a starting point.
AC Tonnage by Room Size: Sizing Chart and How to Calculate It
How to size AC tonnage by room or house square footage. A square-footage-to-tonnage chart, the 20 BTU per sq ft rule, climate adjustments, and why room-by-room sizing beats rules of thumb.
Fan Laws Explained: How Blower Speed Affects Airflow
The three fan affinity laws relate blower speed to airflow, static pressure, and power. Why a 10% speed increase costs 33% more power, with worked examples.
What Is CFM and How to Calculate It
CFM is the volume of air your HVAC system moves per minute. What it means, the 400 CFM per ton rule, the formula to size airflow per room, and how to measure it.
Refrigerant Overcharge vs Undercharge: How to Tell
How to tell if an AC is overcharged or undercharged using superheat and subcooling, the symptoms of each, and why airflow must be verified before touching the charge.
How Many BTU Do I Need? AC Sizing for Every Room and Home
The right BTU for any room or home — the 20 BTU rule, adjustments for climate, ceiling height, sun, and insulation. Includes a quick-reference size table and worked examples.
Manual J vs Rule of Thumb: When to Use Each
Manual J is a room-by-room load calculation; rules of thumb estimate tonnage from square footage. How each works, why oversizing hurts, and when each is appropriate.
What Size Heat Pump Do I Need? A Guide for Cold Climates
Size a heat pump for both cooling and heating with balance-point analysis for cold climates, climate zone factors, and when to add backup heat.
Furnace Sizing Guide: What Size Furnace for My House?
Find the right furnace BTU for your home by climate zone and insulation with AFUE adjustment, worked examples, and why oversizing is the most common mistake.
HVAC Delta T: Normal Range and What a Bad Reading Means
What Delta T (temperature split) means for AC and furnaces, the normal ranges, how to measure it, and what high or low readings tell you about a system.
Superheat vs Subcooling: A Field Guide for HVAC Techs
What superheat and subcooling mean, how to measure each, normal target ranges for TXV and fixed-orifice systems, and what readings tell you about refrigerant charge.
SEER vs SEER2: What Changed and Does It Actually Matter?
SEER2 replaced SEER as the federal efficiency standard in 2023. What changed, how to convert between them, and whether the difference matters when buying.
Is a 95% AFUE Furnace Worth the Extra Cost?
Compare 80% vs 96% AFUE furnaces on fuel cost, payback period, and 15-year total cost. Worked examples for cold and mild climates at different gas prices.
How Much Does a New HVAC System Cost in 2025?
Installed cost ranges for central AC, furnaces, heat pumps, and full systems in 2025 by size, efficiency tier, and region. What drives the price up or down.
Markup vs Margin: How HVAC Contractors Should Price Jobs
The difference between markup and margin, why most HVAC contractors underprice jobs, and how to calculate the right selling price to hit your target profit.
HVAC Static Pressure: How to Test It and What the Numbers Mean
How to measure total external static pressure (TESP), the normal range for residential systems, and how high or low readings point to specific duct and equipment problems.
Mini-Split vs Central Air: Which Is Right for Your Home?
A direct comparison of ductless mini-splits vs central air — upfront cost, operating efficiency, installation, comfort control, and which wins in each scenario.
HVAC Duct Sizing: Manual D vs Rules of Thumb
How to size HVAC ducts using the Manual D friction rate method and simplified rules of thumb, with duct velocity limits and why wrong sizing causes comfort problems.
HRV vs ERV: Which Recovery Ventilator Does Your Home Need?
Heat Recovery Ventilators vs Energy Recovery Ventilators — how they work, what each recovers, which climate conditions suit each, and how to size them.
Heat Pump vs Gas Furnace: Which Is Cheaper to Run?
Side-by-side operating cost comparison of heat pumps and gas furnaces by climate, electricity rate, and gas price. Break-even analysis and when each wins.
ASHRAE 62.2 Ventilation Requirements: What Your Home Actually Needs
The ASHRAE 62.2 whole-building ventilation formula, why tight construction requires mechanical ventilation, and how to size an HRV, ERV, or exhaust fan to meet the standard.