Manual J load calculationsmade easy.
Run accurate residential Manual J HVAC load calculations online in a few minutes. Get room-by-room loads and clear reports you can share with homeowners and permit offices.
Unlimited basic Manual J-style calculations with smart defaults. Pro unlocks advanced inputs and branded load reports—no credit card required to start.
Load Calc Guru is an online Manual J HVAC load calculator for HVAC contractors, combining free unlimited basic Manual J-style calculations with smart defaults and an affordable Pro plan that unlocks full HVAC load calculation software features—advanced Manual J inputs, blower door integration, custom design conditions, multi-system splits, and branded PDF reports—for accurate room-by-room BTU/hr heat loss and heat gain, sensible and latent loads, and clear reports to right-size heat pumps, air conditioners, and furnaces on every residential project.
Save money on HVAC
Oversized HVAC systems short-cycle, cost more up front, and waste energy. Undersized equipment struggles on design days. Our Manual J load calculation software sizes each system to the actual design heating and cooling load so you avoid callbacks, reduce utility bills, and stop guessing at "tons per square foot".
Accurate by design
Load Calc Guru applies ACCA Manual J methodology for every room. You can account for envelope R-values, window performance, shading, infiltration (including blower door results), internal gains, and climate design temperatures. The result is professional-grade residential HVAC load calculations you can defend to homeowners, building officials, and energy programs.
Free basic, Pro advanced
Run unlimited basic load calculations for free using carefully tuned defaults that work for most homes. When you need full control, Pro unlocks advanced Manual J inputs, blower door integration, custom design temperatures, multi-system splits, detailed room-by-room reports, and branded PDFs - everything you expect from serious HVAC load calculation software for a fraction of the usual price.
1) Describe the home
Enter the address or climate city, number of floors, square footage, and rooms. Use presets for common construction types or override wall, roof, floor, and window details when you need more precise Manual J inputs for your load calculation.
2) Pick design conditions
Choose recommended ASHRAE-style design temperatures for your location or set custom summer and winter design dry-bulb and indoor setpoints. Load Calc Guru uses this weather data to calculate peak heating and cooling loads so your HVAC equipment is sized for real-world extremes.
3) Get room-by-room loads
Instantly see room-by-room heat loss and heat gain, sensible and latent loads, and system totals. Use the room CFM targets to plan ductwork or ductless head sizing, then export a shareable load report or PDF with a single click for proposals and permits.
What is Manual J?
Manual J is the industry standard residential HVAC load calculation method used to determine design heating and cooling requirements for a home. It accounts for how heat flows through walls, roofs, windows, and infiltration so you can select properly sized HVAC equipment that maintains indoor comfort at specific outdoor design temperatures.
- Envelope: wall, roof, and floor R-values and construction type that drive heating and cooling load.
- Windows and doors: U-factor, SHGC, orientation, and shading that affect solar heat gain and heat loss.
- Infiltration and ventilation: natural air changes, mechanical ventilation, or blower door ACH50 values.
- Internal gains: people, lighting, appliances, equipment.
- Climate: outdoor design temps and humidity by location.
Accurate Manual J load data gives you confidence to choose the right tonnage for heat pumps, furnaces, and air conditioners. It prevents oversizing that hurts dehumidification and shortens equipment life, and avoids undersizing that causes comfort complaints on peak design days.
Manual S and Manual D coming soon
After you know the load, Manual S helps select equipment matched to sensible/latent capacity at your design conditions. Manual D sizes ductwork to deliver the required CFM to each room with acceptable friction rate and velocity.
Match coil and condenser, verify capacity at design, check blower performance and dehumidification.
Balance supply/return, set target static pressure, choose trunk/branch sizes, and account for fittings.
Load Calc Guru will unify J, S, and D so contractors and homeowners can go from concept to commissioned system with one workflow.
For HVAC contractors
- Fast Manual J takeoffs for proposals, utility programs, and permit submittals—run a full residential HVAC load calculation in about five minutes on desktop or mobile.
- Branded load calculation PDFs and summaries you can attach to bids, share with building officials, or include in homeowner proposal packets.
- Room-by-room sensible and latent loads with target supply CFM so you can plan duct layouts, ductless head locations, and zoning strategies.
- Full audit trail of Manual J inputs for AHJ review, energy raters, and internal QA—see exactly how each BTU/hr was calculated.
- A streamlined five-minute workflow that fits into your sales and design process instead of slowing it down.
For homeowners and builders
- Right-sized heat pumps, furnaces, and air conditioners instead of oversized “rule of thumb” systems that cost more and perform worse.
- Better comfort and humidity control in every season, with Manual J load data that supports your design decisions.
- Lower energy use and quieter operation from properly sized HVAC systems that match the home's actual heating and cooling load.
- Confidence that the system meets design day demand, supported by a documented Manual J calculation rather than a guess.
No time for load calcs? We'll do the Manual J for you.
Some projects are too busy or too complex to tackle in-house. With Load Calc Guru's white-glove Manual J service, you upload plans and basic project details, and we return a complete residential HVAC load calculation report—ready for equipment selection, homeowner proposals, and permit submittals.
Professional Manual J reports
ACCA-style room-by-room heat loss and heat gain, sensible and latent loads, and system totals, documented in a clean PDF designed for permit offices and clients.
Fast turnaround
Typical turnaround is 24–48 hours for most single-family homes, with rush options available when you are trying to hit a tight bid or permit deadline.
Built on the same engine
Every white-glove project is powered by the same Load Calc Guru engine you can use yourself—so you can move to self-serve Pro mode whenever your team is ready.
Ideal for busy HVAC contractors, design-build firms, energy auditors, and homeowners who need a one-off, permit-ready Manual J without learning new software.
Data and methodology
Inputs
Conditioned floor area and volume, orientation, assemblies, fenestration, infiltration, ventilation, occupancy, lighting, plug loads, and appliances.
Outputs
Peak heating and cooling BTU/hr by room and by system, sensible and latent load split, recommended supply airflow, and notes you can use for Manual S equipment selection and Manual D duct design.
Assumptions
Presets reflect typical code-minimum construction, but you can override any assumption when you know the actual R-values, window specs, or infiltration from a blower door test. Like any Manual J calculator, the quality of the result depends on the quality of the inputs and your local design weather data.
Built for any climate zone
Whether you work in hot-humid Gulf Coast climates, cold-dry northern markets, or mixed climates with big swings between seasons, Load Calc Guru uses appropriate design conditions so your Manual J HVAC load calculations reflect real-world peak demand. You get room-by-room and whole-house loads that make sense for your climate zone.
Hot-humid cooling loads
In hot-humid regions, the latent cooling load matters as much as sensible capacity. Model window SHGC, shading, ventilation, and infiltration so you can choose heat pumps and air conditioners that control humidity, maintain comfort, and avoid oversizing that drives indoor RH up.
Cold-dry heating loads
In cold-dry climates, design heating loads are driven by envelope insulation, air leakage, and window performance. Use Manual J load calculations to see how air sealing, better windows, and exterior insulation change the required furnace or heat pump size at design temperatures.
Mixed climates
Mixed climates need equipment sized for both heating and cooling seasons. Load Calc Guru helps you balance cooling-dominated and heating-dominated loads so you can select heat pumps or dual-fuel systems that perform well year-round without extreme oversizing in either mode.
Ready to size your HVAC system the right way?
Create a professional-grade Manual J load calculation for your next residential HVAC job in just a few minutes. Describe the home, confirm design conditions, and download a clean load report or PDF you can send to homeowners, permit offices, and distributors.
Why Manual J load calculations beat "tons per square foot" rules
Rules of thumb like “one ton per 500 ft²" ignore insulation, windows, air leakage, and climate. Manual J HVAC load calculations use physics instead of guesswork, so the equipment you select matches the home's true heating and cooling demand. That means better comfort, quieter operation, and fewer warranty callbacks.
- Short cycling reduces efficiency and comfort.
- High indoor humidity from insufficient runtime.
- Noisy airflow from oversized blowers and ducts.
- Poor temperature balance between rooms.
Manual J FAQ
How accurate is the calculator?
Like any Manual J HVAC load calculator, accuracy depends on the inputs you provide. When you enter realistic envelope details, window specs, infiltration or blower door results, and occupancy patterns, Load Calc Guru follows the official Manual J formulas exactly to produce precise heating and cooling loads suitable for equipment selection and permit documentation.
What data do I need?
At a minimum you need the address or climate city, basic construction type, approximate insulation levels, window areas and types, and typical indoor setpoints. For best results, add blower door test data, known R-values, and accurate window U-factor and SHGC from the window schedule.
Can I model heat pumps?
Yes. Load Calc Guru is equipment-agnostic. The Manual J load report gives you heating and cooling BTU/hr by room and by system, plus sensible and latent splits, so you can apply Manual S to verify that your chosen heat pump or air conditioner has enough capacity at outdoor design and low-ambient conditions.
Does this handle additions or partial remodels?
Yes. You can model additions, finished basements, or partial remodels by creating zones or systems for the areas you are changing. Use the load report to decide whether to tie into an existing system, add a ductless mini-split, or design a dedicated system for the new space.
Do you support humidity control?
Cooling outputs include sensible and latent loads so you understand how much capacity is needed to control temperature and humidity. This helps you select equipment with appropriate sensible heat ratios and match dehumidification performance to your climate and building type.
Can I export a PDF?
Yes. Pro users export branded PDF load calculation reports and share read-only links with clients, building officials, and energy program reviewers directly from Load Calc Guru.
Is there a free plan?
Yes. Unlimited basic Manual J-style calculations are free so you can sanity-check equipment sizing and explore “what-if” scenarios without friction. When you are ready for advanced inputs and polished reports, upgrade to Pro.
When will Manual S and D be available?
Manual S equipment selection is the next major feature we are building, followed by Manual D duct design workflows. Our goal is to provide a full J-S-D toolchain so you can go from load calculation to equipment selection and duct sizing in one place.
Run a Manual J in five minutes
Create your free account and size your next heat pump, furnace, or AC with confidence. Share the report or export a PDF in a click.