SizingKitHVAC · load schedule
HVAC load calculator with the sensible and latent split kept apart
Free, no signup: build a room schedule and this returns heating BTU/h, sensible cooling BTU/h and latent cooling BTU/h for every room and for the house, plus the sensible heat ratio the equipment has to match. Conduction comes from whole-assembly U-factors with the framing counted, ventilation from the ASHRAE 62.2 rate, moisture from the difference in grains between your outdoor design wet bulb and the indoor design condition. Solar gain is the one term it does not compute, and it says so beside the total rather than hiding a guess in it.
- 100% free
- No signup
- Sensible, latent and SHR
- Per-room and whole-house
- Altitude-corrected air factors
- Printable schedule
Design conditions
The two indoor figures are Manual J defaults and are editable. The three outdoor figures are yours: they are prefilled so the page has something to show, and they are almost certainly not your station.
ASHRAE 99% heating dry bulb for your station.
Default 70 °F — A design assumption. Manual J permits another value where the owner asks for one; the load moves by roughly 2–3% per degree.
ASHRAE 1% cooling dry bulb.
The only input the latent column depends on.
Default 75 °F — A design assumption, and the one most often argued about — a household that keeps the house at 72 °F has a larger cooling load than this default computes.
ACCA Manual J, Table 1: the default indoor design relative humidity for cooling, 50%.
Moves the air-side factors, not the fabric loss.
Sets the 62.2 ventilation default below.
Whole-assembly U with the framing counted, not the batt label.
BTU/(h·ft²·°F). Your figure wins over the select above.
Center of glass. An NFRC label figure is better and is worse.
Type the U-factor off the NFRC sticker if you have it.
Default R-28.2 effective from R-31.1 nominal.
Default 54 CFM from ASHRAE 62.2 Eq. 4.1a. Leakage is on top of it and comes from a blower door.
Room schedule
Wall area is net of the glass in it. Ceiling area is only where the room is under the roof or an unconditioned attic; a room with conditioned space above it takes zero.
| Room | Floor ft² | Wall ft² | Glass ft² | Ceiling ft² | People | Equip. W | Solar BTU/h | Remove |
|---|---|---|---|---|---|---|---|---|
The load
Heating
12,211 BTU/h
3.58 kW
Cooling, total
11,331 BTU/h
0.94 tons · 3.32 kW
Sensible heat ratio
0.79
8,934 BTU/h sensible, 2,397 BTU/h latent
| Room | UA | CFM | Heating | Sensible | Latent |
|---|---|---|---|---|---|
| Living | 88.6 | 21.5 | 5,319 BTU/h | 2,197 BTU/h | 1,073 BTU/h |
| Kitchen | 40.2 | 12.1 | 2,413 BTU/h | 4,778 BTU/h | 266 BTU/h |
| Bed 1 | 40.6 | 11.4 | 2,435 BTU/h | 1,150 BTU/h | 651 BTU/h |
| Bed 2 | 34.1 | 9.4 | 2,044 BTU/h | 809 BTU/h | 407 BTU/h |
| Whole house | 54 | 12,211 BTU/h | 8,934 BTU/h | 2,397 BTU/h |
What the answer rests on. Heating runs at a 60.0 °F / 33.3 °C difference and cooling at 17.0 °F / 9.4 °C, both of them differences and neither converted with the absolute scale. Moisture to remove: 32.7 gr/lb. The air-side factors are 1.068 sensible and 0.675 latent, recomputed at 0 ft and 75 °F rather than taken as 1.08 and 0.68.
Solar gain is not computed here. A cooling load needs area × SHGC × the peak irradiance for that orientation and latitude, and this site does not carry an irradiance table or the Manual J glass-load multipliers — so the column takes your figure and defaults to zero. You have entered none, so read the cooling total as a floor: the term missing from it is the one Manual J calls the largest single cooling term in most houses.
Glazing U-factors above are generated, not looked up: single glazing is 0.68 interior film + 0.17 exterior film at 15 mph, double glazing the same two films plus 1 for the non-reflective air space. Both are center-of-glass and ignore the conduction of the glass itself, which is under 4% of the total. The frame is not in them, which is why an NFRC whole-window U-factor from the sticker is both more accurate and numerically worse. Low-emissivity coatings move the air-space resistance by a factor that depends on the surface emittance, so they are not offered — take that number off the label. Ceiling default: R-31.1 nominal falls to R-28.2 effective once the joists are counted, a 9% loss at the ASHRAE 90.1 ceiling framing fraction of 0.11.
Design temperatures. The two prefilled outdoor figures are placeholders so that the schedule has something to compute, and they are not your weather: look your own station up in the ASHRAE climatic design tables and replace them before the totals mean anything. What the schedule does next is equipment: turn the heating figure into a furnace rating, or check the cooling total against the Manual S bounds on a selection.
The eight components, and which of them this page carries
| Component | Kind | What it is |
|---|---|---|
| Wall, ceiling and floor conduction | sensible | U × A × ΔT for every assembly, at the whole-assembly U-value including framing — not the R printed on the batt. |
| Window and door conduction | sensible | U × A × ΔT at the NFRC whole-window U-factor, which includes the frame and is worse than the center-of-glass figure. |
| Solar gain through glazing | sensible | Area × SHGC × the peak irradiance for that orientation and latitude. The single largest cooling term in most houses, and the one a square-foot rule cannot see at all. |
| Infiltration | both | Sensible 1.08 × CFM × ΔT and latent 0.68 × CFM × Δgrains, from a leakage estimate or from a measured blower-door result. |
| Mechanical ventilation | both | The same two equations on the deliberate outdoor air — ASHRAE 62.2 in a house — less whatever an ERV or HRV recovers. |
| Duct loss and gain | both | Conduction and leakage from ducts outside the conditioned envelope. In a vented attic this can be a fifth of the whole load; in conditioned space it is nearly nothing. |
| Occupants | both | 230 BTU/h sensible and 200 latent each, at bedrooms + 1. Ignored in heating, because a load calculation must not depend on somebody being home. |
| Appliances and lighting | both | Kitchen equipment, plug loads and lighting. Ignored in heating for the same reason. |
The load components of an ACCA Manual J (8th edition) residential load calculation, in the order a room-by-room worksheet takes them. Ventilation default: 0.03 CFM per ft² plus 7.5 CFM per occupant at bedrooms plus one.
How to build a load schedule that holds together room by room
The order matters: conditions first, then fabric, then the rooms.
Replace the two outdoor design temperatures with your station's
The winter figure is the ASHRAE 99% heating dry bulb and the summer pair is the 1% cooling dry bulb with its mean coincident wet bulb. They come from the climatic design tables by weather station, and an airport figure can be several degrees off a site twenty miles away at a different elevation. The wet bulb is the only input the latent column depends on.
Set the three U-factors from what the building is actually made of
Pick a wall assembly and the whole-assembly U appears with the framing already counted; type over it if you know better. The glazing default is a center-of-glass figure built from the surface films, so an NFRC number off the window sticker beats it. Ceiling area counts only where a room sits under the roof or a vented attic.
Enter each room, then read the ratio rather than the total
Wall area is net of the glass in it. When the schedule fills in, the number to look at is the sensible heat ratio at the top right: it is what tells you whether the equipment that matches your tonnage will also remove the water, and it is the figure a whole-house estimate cannot produce at all.
Technical specifications
| Outputs per room | Heating BTU/h, sensible cooling BTU/h, latent cooling BTU/h, the room's UA in BTU/(h·°F) and its share of the ventilation airflow in CFM. Rooms are added and removed freely; the schedule prints on one sheet. |
|---|---|
| Ventilation default | ASHRAE 62.2 Eq. 4.1a — 0.03 CFM per ft² of floor plus 7.5 CFM per occupant at bedrooms plus one. The area term was 0.01 CFM/ft² before 62.2-2013, so an older reference gives a much smaller figure. |
| Air-side factors | Computed as 60 × air density × specific heat at the elevation and indoor temperature entered, not fixed at 1.08 and 0.68. At 5,280 ft and 75 °F indoors the pair reads 0.880 and 0.556 against 1.068 and 0.540 at sea level — an 18% error if the standard figures are used in Denver. |
| Glazing U-factors | 1.18 single and 0.54 double, generated from the ASHRAE surface films — 0.68 interior, 0.17 exterior at 15 mph — with 1.0 for a nominal 3/4 in non-reflective air space between panes. Center of glass, frame excluded. |
| Ceiling default | 12 in of blown fiberglass in a wood-framed ceiling: R-31.1 on the cavity path, R-28.2 effective once the joists are counted at the ASHRAE 90.1 framing fraction of 0.11 — a 9% bridging loss, against 24% for the same arithmetic on a 2×4 wall. |
| Moisture arithmetic | Humidity ratio from the Hyland–Wexler saturation-pressure formulation at the site's barometric pressure, converted to grains per pound at 7,000 grains to the pound. The latent term is the outdoor minus indoor difference in grains, and it goes to zero rather than negative in a dry climate. |
| Elevation range | Sea level to 15,000 ft, through the ASHRAE Handbook—Fundamentals barometric equation. Elevation moves the air-side terms and leaves the fabric conduction alone. |
| Not computed | Solar gain through glazing, duct loss and gain, and any infiltration beyond the ventilation rate you enter. The first of those is the largest single cooling term in most houses, and the field for it defaults to zero. |
Frequently asked questions
What is the sensible heat ratio and why is it the number to read?
It is the sensible load divided by the total, and it is what decides whether a correctly sized machine still leaves the house damp. Cooling equipment removes heat and water in a fixed proportion set by its coil temperature and airflow, typically around 0.75 to 0.80 sensible at rating conditions. A house in a humid climate with a computed ratio of 0.68 needs equipment selected for its latent capacity, not just its tonnage, and equipment chosen on tons alone will hold the thermostat setpoint at 60% relative humidity.
Why does it ask for a wet bulb temperature as well as a dry bulb?
Because dry bulb alone says nothing about how much water is in the outdoor air. 95 °F at a 78 °F wet bulb in Houston and 95 °F at a 65 °F wet bulb in Phoenix are the same sensible load and completely different latent loads — about 122 grains per pound against about 55. The mean coincident wet bulb published alongside the 1% dry bulb is the pairing that actually occurs, which is why it is used rather than the highest wet bulb of the year. The relationship between the two readings is what the psychrometric chart is, and the state point behind this arithmetic is what the psychrometric calculator plots.
Do I have to fill in the solar column?
You do if you want a cooling total you can act on. This site does not carry the glass-load multipliers or the clear-sky irradiance by orientation and latitude that the term needs, and it will not invent them, so the field takes your figure — from load-calculation software, from the ACCA glass tables, or from area × SHGC × a peak irradiance you have looked up. Left at zero, the sensible column is the conduction and ventilation floor and nothing more.
Which rooms get a ceiling area?
Only the ones with unconditioned space or outdoors directly above them. A first-floor bedroom under a second-floor bedroom loses no heat upward that the house does not immediately get back, so its ceiling area is zero and its floor area is zero for the same reason. A single-storey house has a ceiling area in every room; a two-storey house has one only upstairs, and the ratio between the two floors is usually the single biggest surprise in a first schedule.
Why does site elevation change the answer at all?
Because the airflow terms are mass flow wearing volume units. 1.08 is 60 minutes per hour times 0.075 lb/ft³ times 0.24 BTU/lb·°F, and the density in the middle is the one thing that moves — thinner air carries proportionally less heat per cubic foot. A Denver system moving 400 CFM is moving about 18% less air by weight than the same 400 CFM at sea level, so it removes about 18% less heat, and the correction is why this page recomputes the factors rather than storing them.
Should the ventilation figure include air leakage as well?
Yes, and the default does not — you have to add it. The 62.2 number is the deliberate outdoor air a dwelling is required to move, and unintentional leakage is separate, comes from a blower-door result run through an infiltration model, and is not on this site. In an older house it can exceed the ventilation rate several times over; in a tight new build the blower door will show it to be nearly nothing, which is the whole reason mechanical ventilation became a requirement.
Is a room-by-room load the same thing as a duct design?
No — the load is the input to the duct design, not the design. Once each room has a sensible load you divide it by the supply air temperature difference to get the room's CFM, and only then does duct sizing begin against a friction rate and a velocity limit. The airflow conversion is what the CFM calculator does, and the branch and trunk sizes that follow are a separate procedure again.
Sensible, latent, and why the split has to survive to the end
Every cooling load is two loads that happen to be measured in the same unit. Sensible heat changes the temperature of the air and is what a thermostat responds to; latent heat changes how much water the air is carrying and a thermostat cannot see it at all. Add them together too early and you get a total that looks like an equipment size and has lost the information that decides comfort. This is why the schedule here carries three columns to the bottom of the page instead of one, and why the ratio between them is printed larger than either — a house that needs 32,000 BTU/h at a ratio of 0.72 and a house that needs 32,000 at 0.85 are not the same job, and only the second one is safely served by picking equipment on tonnage.
The reason for doing it room by room rather than for the house as a whole is that the room is where the air has to arrive. A whole-house figure tells you what machine to buy; a per-room figure tells you how much of its air each room needs, which is the input the duct layout is designed against and the reason the bedroom over the garage is cold in February. The two answers also disagree in a way that is diagnostic: if one room comes out at a third of the house’s load on a tenth of its floor area, the schedule has just found the west-facing glass, the uninsulated bay or the ceiling under a vented attic before anybody went and stood in it. That per-room airflow is worked out from the room’s sensible load and the supply temperature difference, which is what the CFM calculator does with the same 1.08 factor this page derives.
One honest limit, stated plainly because the alternative is a number with nothing behind it: the moisture side of this calculation is only as good as the outdoor design wet bulb you supply, and the state that wet bulb implies — the humidity ratio, the dew point, the enthalpy — is a piece of psychrometrics rather than of load calculation. If you want to see the state point itself rather than the grains figure this page extracts from it, the psychrometric calculator plots it. And if what you actually need is the winter half of this in metric, with U-values and areas rather than a room schedule, the heat loss calculator is the same physics arranged for that question, while the Manual J page sets out what a certified calculation adds that neither of them can.
Where the room schedule lives
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.
The schedule exists only in this tab’s memory and is gone on reload — it is not saved to the browser, to an account or to anything else, so copy it out with the button above the totals before you close the page.