About In-House Engineer

Why this site exists

I do HVAC design for a living — load calculations, duct and piping layouts, energy calculations, commissioning. Over the years the same questions kept arriving from clients, contractors and homeowners, and when I went looking for something to point them at, what I found online was usually one of two things.

Either a calculator with no stated method, no source, and no way to tell whether it was right — or a correct explanation buried in a textbook nobody outside the field is going to open.

These tools are my attempt at the missing third option: give the number, show the method, and explain what the number actually means for the building.

How the tools are built

Published formulations, not approximations

Where a governing standard exists, it gets used directly rather than curve-fitted. The psychrometric tools use the ASHRAE Hyland-Wexler saturation formulation with the Buck enhancement factor. Pipe and duct pressure loss use Darcy-Weisbach with an iteratively solved Colebrook friction factor rather than an explicit approximation. Refrigerant properties come from multiparameter Helmholtz equations of state, the same formulations underlying NIST REFPROP.

Everything gets checked against something independent

A formula implemented correctly and a formula implemented as intended are different things. Each tool is validated against a reference I can cite:

• Duct pressure loss — checked at six points against the ASHRAE Fundamentals friction chart
• Pipe friction factors — checked against published Moody diagram values
• Refrigerant saturation pressures — checked against published PT data across seven refrigerants
• Psychrometric output — checked against commercial psychrometric software across sixty comparison points

The validation points are printed on each page, with the computed value next to the reference value, so you can see the agreement rather than take my word for it.

When the check fails, the tool changes

The psychrometric calculator originally disagreed with commercial software on humidity ratio by about half a percent while matching exactly on dew point. That signature identified a missing moist-air enhancement factor. The software was right and my implementation was wrong, and it was corrected before publication.

That is the point of validating against something you didn't write.

Nothing you type leaves your browser

Every calculation runs locally in your device. There is no server processing, no submission, and no record of the values you enter — not because of a policy, but because there is nowhere for that data to go. See the privacy page for what is and isn't collected.

What these tools are not

They are screening and reference tools. They are not engineering design, and using one does not create an engineer-client relationship.

• They don't replace a load calculation. The duct calculator sizes a duct for an airflow you supply. Determining that airflow correctly is ACCA Manual J, and no browser tool does it honestly.
• They don't account for the whole system. A correctly sized duct can still be part of a badly unbalanced system. Individual correctness is necessary and not sufficient.
• They aren't a substitute for the governing code, the manufacturer's data, or a stamped design. Where this site and the equipment data plate disagree, the data plate governs.
• They aren't a substitute for a licensed engineer on work where a failure would matter.

Corrections

If you find an error, I want to know. Engineering tools that quietly stay wrong are worse than no tool, and I would rather fix something than defend it. There is a contact page, and a specific report — the inputs you used and the value you expected — is far more useful than a general one.