Manual J Load Calculation for a Utah Permit: What the Plans Examiner Actually Checks

A Utah plan reviewer is not grading your load calculation on style. They are looking for a specific, short list of things, and when a residential HVAC submittal comes back with a correction it is usually one of three: the loads were computed for the whole house instead of room by room, the furnace was compared against its nameplate output instead of its altitude-adjusted output, or the cooling equipment was justified with its rated AHRI capacity instead of its capacity at the actual design conditions. All three are visible on the face of the submittal in about ninety seconds.

Here are the numbers that decide those three questions in Utah, with the document each one comes from.

• Altitude multiplier. Salt Lake City’s own residential HVAC worksheet instructs designers to derate gas appliance input at “4% per 1000’ in elevation” and states plainly that “SLC has a 17% de-ration factor,” giving a multiplier of 0.83 (Salt Lake City Building Services, Residential HVAC Worksheet, updated 12/2012).
• Furnace oversize trigger. On the same worksheet: “If ‘adjusted output’ is greater than 1.4 times the ‘total heating load’, please justify.”
• Cooling oversize trigger. “If ‘cooling capacity’ is greater than 1.15 times the … load, please justify.”
• Design conditions. Salt Lake City International sits at 4,226 ft with a 99 percent heating design dry bulb of 14°F and a 1 percent cooling design dry bulb of 95°F, coincident wet bulb 63°F (ACCA, Outdoor Design Conditions Guide, the standalone edition of Manual J 8th Edition v2.0 Table 1A).
• Which code you are under, as of four weeks ago. Effective 2026-07-01, Utah adopted the 2024 International Mechanical Code, the 2024 International Fuel Gas Code and the 2024 International Energy Conservation Code, while keeping the 2021 International Residential Code (Utah Code 15A-2-103). Pages that still tell you Utah is a 2021 IECC state are describing the code cycle that ended last month.

Below: the twelve Utah weather stations Manual J actually publishes, the climate zone table, and a furnace selection carried far enough to show where the derate flips a passing submittal into a correction.

What Utah law requires, and where the requirement actually lives

The sizing mandate is not in the energy code alone. It is in the residential code you are already building to. Utah Residential Code 2021 Section M1401.3 says heating and cooling equipment “shall be sized in accordance with ACCA Manual S or other sizing methodologies,” with two exceptions worth knowing because they are the legitimate escape hatches:

1. the equipment “utilizes multistage technology or variable refrigerant flow technology and the loads calculated in accordance with the approved heating and cooling calculation methodology are within the range of the manufacturer’s published capacities,” or
2. the manufacturer’s “published capacities cannot satisfy both the total and sensible heat gains calculated in accordance with the approved heating and cooling calculation methodology and the next larger standard size unit is specified”

(Utah Residential Code 2021, Section M1401.3). Section M1401.1 adds the sentence that governs the altitude question later on this page: equipment “shall be installed in accordance with the manufacturer’s instructions and the requirements of this code.”

Above that sits the state adoption. Utah Code 15A-2-103 incorporates specific editions by reference. The version effective 2026-07-01 lists the 2021 IRC, the 2024 IBC, the 2024 IMC, the 2024 IFGC, the 2024 IECC and the 2023 NEC. The version already scheduled for 2027-01-01 keeps that same set. So a 2026 Utah submittal is a 2021 IRC job with a 2024 mechanical, fuel gas and energy code around it, which is an unusual split and one that every load calculation cover sheet should state explicitly, because Salt Lake City’s building services page tells applicants the adopted editions “must be listed on design documents.”

What three real Utah jurisdictions ask you to hand in

Enforcement is local, so the useful thing is not a generalization but the actual checklist language. These are quoted from the jurisdictions’ own published documents.

Three things fall out of that table. The load calculation is a completeness item, not a plan-review comment, so an incomplete packet can be rejected before anyone reads it. Manual J and Manual D are named together, because the room loads feed the duct design. And the energy compliance document (REScheck or equivalent) is a separate line item from the load calculation, which is why handing in a REScheck and calling it done is the single most common packet gap we see.

Salt Lake City’s Residential HVAC Worksheet, line by line

Salt Lake City publishes a four-page Residential HVAC Worksheet, the most explicit public statement we have found of what a Utah plan reviewer wants. It is worth reading even if you are permitting elsewhere in the state, because it shows the arithmetic a reviewer is prepared to check. Everything in this section is quoted from that worksheet.

Room by room is mandatory, and the form says why. “The load calculation must be calculated on a room basis. Room loads are a mandatory requirement for making Manual D duct sizing calculations. This sheet has been developed for hom[e]s built in Utah’s dry climates- do not use for other climate conditions.”

Design conditions have to match Manual J or be defended. The form asks for outside dry bulb, inside dry bulb, design TD and entering wet bulb, then states: “If design conditions used are not those listed in Table 1 / 1A Manual J, please justify.” The instructions expand on it: temperature data “should be from Table 1 or Table 1A of ACCA Manual J,” adjustments are allowed (“there may be areas in the Salt Lake Valley where the low temperature is historically lower than the airport temperature”) but “If values are adjusted- please justify the adjustment.” Entering wet bulb is to be assumed “no higher than 63 °f unless there is ventilation air or significant duct leakage or heat gain.”

Infiltration has to name its method. “Version 7 of Manual J uses Best, Average or Poor to evaluate Infiltration. Version 8AE uses Tight, Semi-Tight, Average, Semi-Loose and Loose.” The permitted methods are the Simplified / Default Method from Table 5A, the Component Leakage Area Method from Table 5C of Manual J8, or a blower door test. Open firebox fireplaces “must be included, even if there is a 4” ‘combustion air’ flex bring[ing] air into the fireplace.” Sealed direct-vent fireplaces are not counted.

Airflow follows from the sensible heat ratio, and then from altitude. The worksheet publishes the rule outright: “If SHR is below 0.80 select 350 cfm / ton; if SHR is between 0.80 & 0.85 select 400 cfm; if SHR is greater than 0.85, select 450 cfm / ton.” Then the Utah correction: “The cooling CFM should be around 450 CFM per ton of cooling in Utah’s dry climates. For higher altitudes, CFM must be adjust[ed] up as detailed in ACCA / ANSI Manual S. Mountain location[s] should expect Cooling CFM at 500 CFM per ton and higher.”

Cooling capacity must come from expanded data, not the box. “Manufacturers base data is based on ARI Standard 210 / 240 ratings; 95 °f outdoor air temperature, 80 °f db / 67 °f wb entering evaporator. As the Design Conditions are different than this standard, refer to manufacturers expanded ratings for capacities at actual design conditions.” And, flatly: “Do not use ARI (A[H]RI) data for actual sizing.” One useful allowance is buried in the same section: “One half of the excess latent capacity may be added to the sensible capacity.”

Manual D is a five-step arithmetic the reviewer can redo. External static pressure, minus total device pressure losses (evaporator, filter, supply register at .03, return grille at .03, other), gives available static pressure. Supply-side total effective length plus return-side TEL gives TEL. Then friction rate FR = (100 x ASP) / TEL, and that FR is “the rate to be used with a duct calculator or a friction chart for the duct design on this project.” A one-line duct diagram with fittings, sizes, equivalent lengths and duct lengths is required as an attachment.

Two cautions about this form, stated plainly. First, its certification line reads “meets the requirements of the 2009 International Mechanical Code and International Fuel Gas Code,” and the sheet is stamped updated 12/2012. Utah is now on the 2024 IMC and 2024 IFGC. Use the worksheet as a guide to what a reviewer checks, not as your code citation. Second, the form field says justify above 1.4 times the heating load while the instruction page works an example at 1.5 times (“If the Total Heating Load = 29954 btuh. A furnace with an adjusted output larger than 45,000 btuh (29954 x 1.5 = 44931) would require an explanation”). Design to the tighter number and the discrepancy never costs you a cycle.

The design conditions: all twelve Utah stations in Manual J Table 1A

This is the table everyone paraphrases and nobody prints. It is ACCA Manual J 8th Edition v2.0 Table 1A for Utah, reproduced from ACCA’s own standalone Outdoor Design Conditions Guide, which exists specifically so that “Raters and Code Officials” can check a designer’s inputs.

Read the table before you read anyone’s summary of it, because four things in it change how a Utah house gets designed.

There is no statewide Utah design temperature, and the ones in circulation are not in the table. One programmatic state-template page that ranks well for these searches publishes a single statewide pair of 6°F winter and 96°F summer. Neither number is the design value of any of the twelve Utah stations Manual J lists. The heating design dry bulbs actually run from 28°F at Saint George to 0°F at Logan-Cache. Against the Manual J default indoor heating condition of 70°F, that is a heating design temperature difference of 42°F in Washington County and 70°F in Cache County, a two-thirds increase in the driving force across one state. A statewide number cannot survive that spread.

Every Utah station has negative design grains. Design grains are the moisture difference between outdoor and indoor air, and ACCA’s note is explicit: “Negative values occur when the outdoor air is dryer than the indoor air.” All twelve Utah stations are negative, at all three indoor humidity assumptions (55, 50 and 45 percent RH). The practical consequence is that infiltration and ventilation air in a Utah summer is a drying stream, not a latent cooling load. Your sensible heat ratio lands high, which by Salt Lake City’s own airflow rule puts you at 450 CFM per ton before the altitude correction, and 500 CFM per ton and up in the mountains. Sizing a Utah system off a humid-climate SHR assumption produces a coil selection and a blower table that are both wrong in the same direction.

Ten of the twelve are high daily range. ACCA defines the categories in the same guide: low is a swing under 16°F, medium is 16°F to 25°F, high is more than 25°F. Only Hill AFB and Wendover are medium. Utah is a high daily range state, which affects the cooling load calculation directly and is one of the reasons block loads and rules of thumb behave badly here.

The heating-to-cooling balance inverts inside the state. The HDD65 / CDD50 ratio runs from 0.49 at Saint George, a cooling-dominated climate, to 3.15 at Logan-Cache, a heavily heating-dominated one. Manual S uses this ratio in equipment selection guidance. A design approach that works in Washington County is the wrong approach in Cache County.

If your site is not in Table 1A

Park City is not in Table 1A, and neither are Heber, Draper, Lehi or Tooele City. Salt Lake City’s instructions anticipate exactly this: “The city or town must be reasonably close to actual location. Software used may not have the specific location in the database,” and any adjusted value must be justified in writing. Do not invent a design temperature for a mountain site. Pick the nearest Table 1A station, state which one, state the elevation difference, and attach the justification. A reviewer will accept a documented adjustment far more readily than an unlabeled number.

Why your HERS rater may be holding a different number

If a rater tells you your heating design temperature is out of range, they are probably reading a different document. RESNET’s Appendix A, “Design Temperature Limits by State and County,” is built from “the 1% cooling and 99% heating design temperatures … in the ASHRAE 2017 Handbook of Fundamentals and Manual J Design Conditions 8th Edition,” and it deliberately takes the extreme of every station within the county or a 40 mile radius: “the highest cooling, lowest heating design temperature … was selected from among these weather stations” (RESNET, Appendix A).

That produces bounds, not design values. Salt Lake County’s limits are 96°F cooling and 11°F heating, against Table 1A’s 95°F and 14°F for the airport, because the heating limit was drawn from Provo Municipal. Washington County’s limits are 109°F and 7°F, because the cooling limit came from Beaver Dam, Arizona and the heating limit from Cedar City Regional, more than 40 miles uphill from St. George. Table 1A says Saint George is 104°F and 28°F.

Two things are happening there at once, and it is worth separating them. Appendix A takes the most extreme station in range, and it reads its temperatures from the ASHRAE 2017 Handbook of Fundamentals, so its number for a station does not have to match the Manual J Table 1A number for that same station: Table 1A puts Provo at 13°F and Cedar City at 9°F. Both documents are correct for their own purpose. Cite the one that matches the reviewer you are talking to, and never average them.

Climate zones, as the code table actually assigns them

Utah’s counties are assigned by the code table, not by elevation intuition, and the assignment is narrower than most summaries suggest. From Table C301.1 of the 2021 Utah Energy Code, “Climate Zones, Moisture Regimes, and Warm Humid Designations by State, County and Territory,” where the B suffix means “Dry” (Utah Energy Code, Chapter 3 General Requirements):

One county in 3B, twenty-one in 5B, seven in 6B, which is all twenty-nine. No Utah county is assigned to zone 4B in this table, which is worth knowing because several widely-ranking pages describe the Wasatch Front as 4B. Salt Lake, Utah, Davis and Weber counties are 5B. The Uinta Basin and the high mountain counties, including Summit and Wasatch, are 6B, and that is where the envelope requirements and the design temperature difference both step up. This table is the 2021 IECC assignment; confirm it against the edition your jurisdiction is reviewing under, since the state moved to the 2024 IECC on 2026-07-01.

The altitude derate, worked

This is the part Utah gets wrong most often, and it is worth being precise, because three different altitude corrections are routinely conflated:

1. the combustion input derate for gas-fired appliances, which is a code and manufacturer requirement,
2. the air density correction to the airflow and psychrometric side of the load calculation, and
3. the capacity derate of refrigeration and cooling equipment, which comes only from the manufacturer’s altitude-corrected performance data.

They are different magnitudes and they are not interchangeable. What follows is item one, because it is the one on the permit form. For the air density side, see our wine cellar cooling unit sizing walkthrough, which works the density ratio and the equipment-capacity question in detail.

The two conventions, and which one Utah uses

The model code language collected on UpCodes reads: “The input rating of appliances operating at elevations above 2000 feet … shall be reduced … At the rate of 4 percent for each 1000 feet above sea level.” Read it carefully. The 2,000 foot threshold decides whether you derate at all. The 4 percent per 1,000 feet is measured from sea level, not from the threshold.

Contractors routinely misread it as 4 percent per 1,000 feet above 2,000 feet, which at Salt Lake City’s 4,226 ft would give 9 percent instead of 17 percent. Salt Lake City’s worksheet settles the question with its own arithmetic: it states a 17 percent deration factor and a 0.83 multiplier for a city at 4,226 ft, which is 4.226 x 4 percent measured from sea level. Its own example: “On a 100,000 Btu furnace you multiply 100,000 x .83 = 83,000 Btu’s.” Note also that IRC M1401.1 requires installation per the manufacturer’s instructions, and the worksheet defers to them too (“Some manufacturers may have different requirements”), including the common 2 percent per 1,000 feet allowance for many 90-plus efficiency furnaces. Where the manufacturer’s instructions differ, they govern, and you attach them.

Sea-level multiplier by elevation, at 4 percent per 1,000 feet

Elevations are the Table 1A station elevations above. Wendover is left out because at 4,236 ft it sits ten feet above the Salt Lake City airport and rounds to the same multiplier.

A furnace selection, all the way through

Take a Salt Lake City house. Design conditions from Table 1A: 4,226 ft, 14°F outdoor at 99 percent, 70°F indoor per Manual J’s default, so a heating design temperature difference of 56°F. Suppose the room-by-room Manual J returns a whole-house heat loss of 48,000 Btu/h. That number is the input to everything below; the point of the example is what happens to it, not the number itself.

Candidate A: 80,000 Btu/h input, 95 percent AFUE.

• Sea level output: 80,000 x 0.95 = 76,000 Btu/h
• Altitude adjusted output: 76,000 x 0.83 = 63,080 Btu/h
• Ratio to load: 63,080 / 48,000 = 1.31, under the worksheet’s 1.4 trigger. No justification required.

Now watch what each mistake does to the same submittal.

Mistake one: submit the nameplate output. 76,000 / 48,000 = 1.58. That is over 1.4, so the reviewer asks for a written justification for an oversized furnace that is not actually oversized. The correction costs a cycle for an arithmetic step that was skipped, not for a design error.

Mistake two: use the wrong derate convention. At 0.91 (the “above 2,000 feet” misreading), adjusted output is 76,000 x 0.91 = 69,160 Btu/h, a ratio of 1.44. Same house, same furnace, same code, and the submittal now trips the trigger. The gap between the two conventions on this one selection is 6,080 Btu/h.

Mistake three, the expensive one: size on the box. A designer trying to hit 48,000 Btu/h might reach for a 60,000 Btu/h input, 95 percent AFUE furnace. Its sea-level output is 57,000 Btu/h, comfortably above the load. In Salt Lake City it delivers 60,000 x 0.95 x 0.83 = 47,310 Btu/h, which is 690 Btu/h short of the design heat loss. The label says 57,000, the house needs 48,000, and on a 14°F morning it still does not make it. Move that same house to Cedar City at 5,617 ft and the multiplier drops to 0.775, delivering 44,175 Btu/h, nearly 4,000 Btu/h short.

Salt Lake City publishes its own version of this arithmetic on the worksheet, and it is worth reproducing exactly because it is the format a reviewer expects to see attached: “Example: 80,000 input 91% efficient furnace in Salt Lake, with manufacturers’ installation instructions specifying 4% / 1000’. 80,000 x .91 x .83 = 60,424 btuh.”

The gas side of the same worksheet carries the derate through to venting and orifice sizing, using 890 Btu per cubic foot and a specific gravity of 0.60 for Salt Lake City, with combustion air computed at 1 square inch per 3,000 Btu of total input for all fuel-burning appliances in the room. If the mechanical sizing sheet and the load calculation disagree about the derated input, the reviewer will find it, because both numbers are on the same four-page form.

A pre-submittal checklist

Run this before the packet goes in. Every item traces to a line quoted above.

• Loads computed room by room, not as a block load, because Manual D needs the room loads
• Outdoor design conditions taken from Manual J Table 1A, with the station named; any adjustment justified in writing
• Indoor conditions stated: 70°F heating, 75°F cooling, with the RH assumption used for design grains
• Entering wet bulb stated, 63°F unless ventilation air, duct leakage or duct heat gain raises it
• Infiltration method named (Table 5A simplified, Table 5C component leakage area, or blower door) and construction quality stated; open-firebox fireplaces counted
• Furnace: sea-level input, AFUE, output, and altitude adjusted output with the multiplier shown and the arithmetic attached
• Adjusted output no more than 1.4x the total heating load, or a written justification attached
• Cooling: capacity from the manufacturer’s expanded performance data at your design conditions, not the AHRI rating, with the specific coil, furnace blower and metering device listed
• Cooling capacity no more than 1.15x the cooling load, or a written justification attached
• Multistage or VRF equipment: state the exception you are relying on under M1401.3, and show both the maximum and the lowest adjusted output
• Airflow: SHR computed, CFM per ton selected from it, and increased for altitude per Manual S (450 CFM/ton in the valleys, 500 and up in the mountains)
• Manual D: ESP, device pressure losses, ASP, supply and return TEL, and FR = (100 x ASP) / TEL, with a one-line duct diagram showing fittings, equivalent lengths and duct lengths
• Energy compliance document (REScheck or equivalent) attached as a separate item from the load calculation
• Code editions listed on the cover sheet: 2021 IRC with the 2024 IMC, IFGC and IECC as adopted 2026-07-01

Where this leaves you

A Utah residential HVAC submittal is not hard, but it is specific, and almost everything that makes it specific is a number that does not appear in national guidance: a design temperature difference that ranges from 42°F to 70°F inside one state, design grains that are negative everywhere so the latent side behaves backwards, a combustion derate measured from sea level rather than from the 2,000 foot threshold, and a code edition set that changed on 2026-07-01. Get those right and the packet clears. Get the derate wrong in either direction and you either justify a furnace that is not oversized or install one that cannot hold 70°F on the coldest morning of the year.

We do this work as the design deliverable: room-by-room Manual J to Table 1A conditions with the station and any adjustment documented, Manual S selection against altitude-corrected and expanded manufacturer data, Manual D duct design with the friction rate worksheet, and the submittal package assembled in the form your jurisdiction reviews. If you are a builder, a GC or an owner staring at a plan-review correction, our load calculation and system design services are the fix, and you can send us the plans to get the numbers started.

For the design side of Utah’s altitude and dry-climate behavior beyond the permit packet, see our Utah climate HVAC design guide, and for how the same derating discipline plays out on a piece of equipment nobody thinks to derate, our wine cellar cooling unit sizing walkthrough.