Reviewer
Tom Hendricks
Sheet metal journeyman, SMACNA, 18 years ductwork
Tom is a sheet metal journeyman who completed a four-year apprenticeship through a SMACNA-affiliated joint apprenticeship and training committee (JATC), the standard path that combines about 8,000 hours of on-the-job training under journeymen with classroom instruction in welding, layout, fabrication, drafting, and HVAC system installation. SMACNA represents over 3,500 contractor companies engaged in sheet metal and air conditioning construction across the United States and Canada, and the journeyman credential is the qualifying tier that lets a worker fabricate and install on commercial projects without supervision.
Tom has spent eighteen years building residential and light-commercial duct systems, which means cutting the trunk and branch runs from raw 28-gauge sheet, hanging it on strap and threaded rod, transitioning to flex at the boots, sealing every joint with mastic or UL-181 tape, and pulling a flow hood at every register before the final invoice. He works to SMACNA HVAC Duct Construction Standards and ACCA Manual D sizing methods on every job. The math on the duct-sizing, static-pressure, friction-loss, and CFM calculators on this site is the math he uses to spec a system before he starts cutting metal.
Tom reviews everything in the Ductwork & airflow category (duct sizing, CFM, static pressure, duct velocity, equivalent length, friction loss, ACH, MERV filter, air balance) plus the diagnostic tools that touch the airflow side of a service call (delta-T, condensate drain sizing, dew point). The radiator BTU sizing tool falls under his review too because finned baseboard and panel radiator sizing uses heat-transfer math that overlaps with airflow heat balance.
Tools reviewed by Tom
Every tool listed below was reviewed by Tom Hendricks against the published code, standard, or manufacturer data it implements. Tom signs off on the math, the inputs that drive it, and the edge cases the result panel flags.
System sizing
Ductwork & airflow
- Duct sizing (Manual D)
- Static pressure calculator
- CFM calculator
- Return air sizing
- Equivalent length calculator
- Friction loss calculator
- Velocity calculator
- Air changes per hour (ACH)
- MERV + air filter
- Furnace filter size finder
- Air balance calculator
- Attic ventilation calculator
- Bathroom exhaust fan calculator
- Range hood CFM calculator
- Zone damper sizing
Refrigerant
Pro tools
Comparison guides reviewed by Tom
Side-by-side comparisons fact-checked by Tom against field experience, install quotes, and manufacturer specs. Each guide covers a real homeowner decision, with the install cost ranges, climate fit, and edge cases verified before publication.
Troubleshooting guides reviewed by Tom
Diagnostic walkthroughs Tom signed off on against the service calls they actually run. Each page lists the real fix order and what every repair costs.
Guides reviewed by Tom
HVAC explainers covering the questions homeowners ask most, fact-checked by Tom against field experience and published code.
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How often should you change your furnace filter?
The change interval by filter thickness, what makes one clog faster, how to tell it is time, what a clogged filter does to your system, and the MERV trap to avoid.
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Which way does a furnace filter go?
The airflow arrow points toward the furnace, in the direction the air flows. How to read it at the furnace slot or a wall or ceiling return, what to do when there is no arrow, and whether a backward filter actually hurts anything.
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Is air duct cleaning worth it, or a scam?
When air duct cleaning is worth the money (mold, pests, after a renovation), when it is a waste, what a real job costs, the scams to avoid, and how to find a company that does it right.
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Why is my upstairs so hot?
Why the upstairs runs hotter than the downstairs, the real causes in order, the free fixes to try first, and the bigger ones (balancing dampers, zoning, insulation, a mini-split) when they are not enough.
How BTU Size uses reviewers
Every tool on BTU Size credits a named technician with field experience in the relevant trade. Reviewers check the math against published code (ACCA, ASHRAE, NEC, NFPA, IECC), against manufacturer engineering data (Carrier, Trane, Mitsubishi, Owens Corning, Slant/Fin), and against the edge cases that show up on real service calls. See the full reviewer roster and methodology.