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HVAC System Analyzer -6 Calculators in One Tool

Cost per BTU, Heat Load, Ventilation, Switchover, Duct Sizing & Room Balancing

A comprehensive HVAC analysis tool with six calculators in one tabbed interface. Compare cost per delivered BTU across fuel sources, estimate heat load from bills, calculate ventilation requirements and air changes per hour, find your mini-split switchover temperature, size round and rectangular ductwork, and balance room-by-room airflow. Everything an HVAC technician, contractor, or serious DIYer needs for a complete system evaluation in a single free tool.

Pro Tip: Start with the Cost per BTU tab to compare fuel options, then use Heat Load Lite to size equipment, then Duct Sizer and Room CFM Balancer to design the distribution system. The tabs work together as a mini design workflow.

Full-featured heat load analysis with benchmarks and ROI

Heat Load from Bills Calculator →

Detailed mini-split cost analysis with 13 COP presets

Mini-Split Efficiency Calculator →

Full payback and NPV analysis for heat pump upgrades

Heating Bill ROI Calculator →
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HVAC System Analyzer
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How It Works

  1. Select a Calculator Tab

    Pick one of six calculators: Cost per BTU, Heat Load Lite, Ventilation/ACH, Switchover Optimizer, Duct Sizer, or Room CFM Balancer. Each tab is self-contained with its own inputs and results.

  2. Enter System Parameters

    Fill in the required inputs for your selected calculator. Cost per BTU needs fuel prices. Heat Load Lite needs bill data. Duct Sizer needs CFM, velocity, and run length. Each calculator has clear labels and tooltips explaining every field.

  3. View Results

    See calculated results instantly. Cost per BTU shows a ranked table. Duct Sizer gives round diameter and rectangular equivalents. Room CFM Balancer shows airflow per room with weighted adjustments for windows, exposure, and ceiling height.

  4. Switch Tabs for Related Analysis

    Move between calculators to build a complete picture. Size the system with Heat Load, compare fuel costs with Cost per BTU, find the switchover temperature, then size the ductwork and balance airflow - all without leaving the tool.

Built For

  • HVAC technicians on job sites needing quick calculations without pulling up multiple apps or spreadsheets
  • Contractors preparing equipment and duct sizing estimates during walk-throughs and site surveys
  • Home inspectors evaluating existing HVAC systems for adequacy, airflow balance, and ventilation
  • DIY HVAC planners designing duct layouts and sizing equipment for renovation or new construction projects
  • Energy auditors running quick fuel cost comparisons and ventilation checks during home assessments
  • Maintenance engineers evaluating industrial HVAC systems for efficiency and airflow distribution
  • Building owners comparing heating fuel options and evaluating system upgrade economics

Features & Capabilities

Cost per Delivered BTU

Compare the actual cost to deliver one BTU of useful heat from electric resistance, heat pump (at a given COP), natural gas, propane, and fuel oil. Accounts for equipment efficiency (AFUE, COP) so you see the real delivered cost, not just the raw fuel price.

Heat Load Lite

A streamlined version of the full Heat Load from Bills calculator. Enter a few months of bill data and your climate zone to get a quick BTU/hr estimate. Great for on-site ballpark sizing when you do not have time for a full analysis.

Ventilation / ACH Calculator

Calculate required ventilation rates and air changes per hour (ACH) based on room volume, occupancy, and use type. Covers ASHRAE 62.1 and 62.2 guidelines for residential and light commercial spaces. Useful for IAQ assessments and makeup air sizing.

Switchover Optimizer

Enter three COP data points (high, mid, low outdoor temps) and fuel prices to find the optimal switchover temperature between heat pump and backup fuel. Uses interpolation for a smooth COP curve instead of a single-point estimate.

Duct Sizer

Enter required CFM, maximum velocity, and available static pressure to get recommended round duct diameter and equivalent rectangular sizes. Accounts for friction loss per 100 feet and shows velocity at the chosen size. Supports both trunk and branch sizing.

Room CFM Balancer

Enter room dimensions, number of exterior walls, window area, ceiling height, and sun exposure for each room. The calculator distributes total system CFM across rooms using weighted factors. Outputs target CFM per room and per register for balanced airflow.

Comparison

Calculator What It Does When to Use It
Cost per BTU Compares fuel cost per delivered BTU Choosing between fuel sources, quoting system types
Heat Load Lite Estimates BTU/hr from bill data Quick equipment sizing on a job site
Ventilation / ACH Calculates air changes and ventilation rates IAQ checks, makeup air sizing, code compliance
Switchover Optimizer Finds heat pump to furnace switchover temp Dual-fuel system setup, thermostat programming
Duct Sizer Sizes round and rectangular ductwork Duct design, renovation, adding branches
Room CFM Balancer Distributes system airflow by room New installations, comfort complaints, rebalancing

Frequently Asked Questions

Yes. They are organized in tabs within a single interface. Click a tab to switch between calculators. Each one is fully functional with its own inputs and results. No pages to load, no tools to switch between.
If you are evaluating a heating system upgrade, start with Cost per BTU to compare fuel economics, then Heat Load Lite to size the equipment. If you are designing ductwork, start with Duct Sizer for trunk and branch sizing, then Room CFM Balancer for airflow distribution.
This tool provides planning-level estimates suitable for preliminary design and customer proposals. For permit applications, most jurisdictions require a full Manual J load calculation and Manual D duct design performed by a licensed professional. Use this tool to get in the right ballpark before running formal calculations.
The Duct Sizer calculates friction loss for straight duct runs. For fittings, use the equivalent length method - each elbow, tee, or transition adds equivalent feet of straight duct. A standard 90-degree elbow equals roughly 10-15 feet of equivalent length depending on duct size.
Absolutely. Enter your total system CFM (from the blower spec) and your room dimensions to see what each room should be getting. Then measure actual airflow at each register with an anemometer. The difference between target and actual tells you where damper adjustments or duct modifications are needed.
Yes. The tabbed interface is designed to work on phones and tablets. You can run calculations on-site during a walk-through without needing a laptop. All calculations happen in your browser - no internet connection required after the page loads.
You can use your browser's print function to save results as a PDF. Full export functionality is planned for a future update. For now, screenshots or browser print work for including results in proposals and reports.
Duct size depends on the CFM (cubic feet per minute) each branch needs to deliver and the maximum velocity you want to maintain. For residential trunk ducts, 6-inch round handles about 100 CFM, 8-inch handles about 160 CFM, 10-inch about 250 CFM, and 12-inch about 375 CFM at standard velocities. Branch runs to individual rooms are typically 4-8 inches depending on the room's CFM requirement. Use the Duct Sizer tab in this tool to calculate the correct diameter for your specific CFM and static pressure conditions.
Air changes per hour (ACH) equals the total airflow in CFM multiplied by 60, divided by the room volume in cubic feet. For example, a 12x15 room with 8-foot ceilings is 1,440 cubic feet. If your supply register delivers 80 CFM, that is 80 times 60 divided by 1,440, which equals 3.3 ACH. ASHRAE recommends 0.35 ACH minimum for residential ventilation. Most forced-air HVAC systems deliver 4-8 ACH when the blower is running. Use the Ventilation/ACH tab to calculate this for any room.
Disclaimer: All calculators in this tool provide estimates for planning and preliminary design purposes. Results are not a substitute for professional engineering calculations required for permits, code compliance, or final system design. Duct sizing, load calculations, and ventilation requirements should be verified by a licensed HVAC contractor or professional engineer for any permitted work.

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