Jonathan Stowe

Background

I am a homeowner who got tired of contradictory HVAC contractor quotes during a system upgrade and decided to learn the underlying methodology myself. Three contractors visited; three different tonnage recommendations came back — 2.5 tons, 3.5 tons, and 4 tons for the same house. None of them performed a Manual J calculation. None of them documented their reasoning. One said "rule of thumb is 1 ton per 600 square feet" and quoted from that.

The disparity bothered me enough to start reading. The primary sources I worked through:

• ACCA Manual J 8th Edition — the standard methodology for residential load calculation in the US.
• ASHRAE Handbook of Fundamentals 2021 — psychrometrics, design temperatures, and climatic data the Manual J calculation depends on.
• NEEP CCASHP specifications — cold-climate heat pump performance data that mattered for my specific climate.
• DOE Energy Saver consumer guides — the federal incentive landscape.
• NFRC certification documentation — window U-factor and SHGC ratings that drove envelope calculations.

After a few months of reading, I had a working understanding of why my three quotes diverged: one contractor was sizing aggressively (probably padding for callbacks), one was rule-of-thumb, one was closer to a real Manual J but still missing infiltration measurement. I picked equipment that matched what the actual Manual J indicated, with a contractor willing to work to those numbers.

The experience left me with two beliefs that drive this site. First, the methodology is learnable for non-professionals willing to read primary sources. Second, the educational gap between rule-of-thumb online calculators and permit-grade ACCA-approved software leaves homeowners without a useful middle ground. hvacloadcalc.org tries to be that middle ground.

Why This Site Exists

The HVAC reference space online has three structural problems and one missing piece.

Calculator sites (Calculator.net, Omnicalculator, MiniWebtool) publish "Manual J calculators" that use rule-of-thumb math with no documented methodology and no acknowledgment of uncertainty. The output is misleading to homeowners who think they have a load calculation when they have a square-footage-times-a-constant guess.

Contractor software (Cool Calc, AutoHVAC, ServiceTitan) is paywalled, homeowner-hostile, and B2B-only. The methodology is good — these are ACCA-approved tools — but the access model excludes the homeowner audience entirely.

Manufacturer sites (Trane, Carrier, Lennox) carry built-in bias toward their own equipment. Even when content is technically accurate, the framing pushes purchase decisions. The marketing-first approach makes them poor sources for objective comparative research.

The missing piece: a methodology-transparent, primary-source-cited, homeowner-first reference covering Manual J / Manual S / Manual D / Manual T plus the building science that drives sizing. That is what hvacloadcalc.org is trying to be.

The audience I write for is homeowners who want to verify whether a contractor recommendation makes sense, understand whether a heat pump or furnace upgrade is appropriate for their specific situation, learn the underlying methodology well enough to ask better contractor questions, and look up authoritative reference data (R-values, design temperatures, federal incentive amounts) when they need it.

Research Approach

My research approach has three rules.

(1) Primary sources first. When a claim has a tier 1 source available (ACCA Manual, ASHRAE Handbook, AHRI standard, NFRC documentation, DOE Final Rule, EPA regulation, IRS Fact Sheet), I cite tier 1 even if a tier 2 source explains the same fact more accessibly. Tier 1 sources are revision-tracked by standards organizations and remain authoritative through revision cycles.

(2) Read the standard, not the summary. The temptation when writing reference content is to summarize a secondary summary. I try to read the primary standard directly. When ACCA Manual J Section 8 covers infiltration methodology, I read Section 8 rather than reading a contractor's summary of Section 8. The depth of citation reflects that — every inline SourceCite resolves to the actual primary document, not to a derivative explanation.

(3) Quote-extractable language. Every definition, every formula, every threshold is written so it can be lifted out of context and stand on its own. An LLM extracting "what is HSPF2" should be able to take the first sentence of my definition and have a coherent, sourced statement. The constraint forces clarity at the sentence level and avoids the wandering paragraph problem common in technical writing.

The research approach is slow. A hero-depth article takes 8-15 hours of editorial work plus the underlying primary-source reading, which can be substantially longer for novel topics. The slowness is the cost of accountability — every claim is defensible against a primary-source check, and that defensibility requires that the author actually read the primary source.

How I Work

A few things about how I work that shape what you'll find on the site (and what you won't).

I write reference content, not consultations. The calculators and articles produce planning-grade output sufficient for evaluating contractor quotes and understanding magnitudes. For permit-grade Manual J on a specific home, hire a credentialed party using ACCA-approved software — I do not offer one-on-one consulting on a paid or unpaid basis, and individual sizing requests by email get redirected to the relevant calculator.

I do not recommend specific equipment brands or models for specific homes. Equipment performance for any specific household depends on local climate, electricity and gas prices, contractor availability, and other factors I cannot evaluate from a contact email. The content points at authoritative product lists (ENERGY STAR Most Efficient, NEEP CCASHP product list, AHRI Directory) where every qualifying model is independently verified.

I do not maintain a contractor directory. Readers looking for a contractor should start with their state HVAC licensing board, credentialing programs (RESNET HERS raters, BPI Building Analysts, NEEP CCASHP installer locator), or their state energy office's list of HEEHRA-participating contractors. Those sources have screening and accountability that an editorial reference site cannot provide.

I do read every substantive correction and methodology feedback. The corrections process is documented at /corrections/ and the editorial process at /editorial-standards/. If you find something wrong, tell me — the site improves through reader feedback and the credit for catching errors gets attributed publicly when reporters opt in.

Scope and Limits

To be explicit about what this site is and is not.

This is a reference site for residential HVAC sizing and methodology, written for homeowners and produced through primary-source research. It is not a substitute for credentialed professional work where credentialed work is required: permit-grade Manual J calculations need ACCA-approved software run by a contractor or HERS rater, equipment installation requires a licensed HVAC contractor, and safety-critical work (refrigerant handling, electrical, gas connections) requires the relevant trade credential.

The calculators on the site produce planning-grade output appropriate for understanding magnitudes (2-ton vs 3-ton, R-30 vs R-49), evaluating contractor quotes, and budgeting equipment purchases. They are not appropriate for permit applications, rebate documentation, or anything where ACCA-approved software output is required. The methodology page describes the accuracy bands the calculators claim and the verification against ACCA reference cases.

What I do claim: that rigorous research into primary sources produces educational content that helps non-specialists make better decisions about residential HVAC. The claim is testable — every article has SOURCES, every claim has SourceCite, every conclusion can be verified against the cited source. If the source check fails, the claim is wrong and the corrections process applies.

Published Articles

The published content set as of 2026-05-30:

The publishing pace targets one new article or hub per week with occasional bursts for clustered topics. The total content set grows over time; the existing content gets annual review with updates when standards revise.

Corrections and Feedback

If you find something inaccurate on the site, email info@hvacloadcalc.org with subject "Correction" and include:

(1) The specific URL where the error appears.

(2) The exact quoted text you believe is incorrect.

(3) The corrected text you believe is right.

(4) The source supporting the correction (a primary source if possible; tier 2 sources if tier 1 does not address the specific point).

I acknowledge correction reports within 14 days. Valid corrections are implemented (article updated, last-reviewed date refreshed) and logged at /corrections/ with the original claim, the corrected claim, the date, and — with your explicit consent — attribution by name and affiliation. If you prefer not to be attributed, the correction is still logged but without your name.

For methodology disagreements (where reasonable practitioners might read the same standard and reach different conclusions), I evaluate the disagreement against the source, either implement the suggested change or defend the original position with citation, and respond substantively within 60 days. If the disagreement is genuinely contested in the field, the article gets a note documenting the position rather than asserting one position as fact.

For non-correction feedback (general questions, topic suggestions, methodology questions), the response timeline is best-effort rather than guaranteed. The site is small and individual question response is not always possible, but substantive feedback is read.