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.
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MERV vs MPR vs FPR
Three filter scales, one real standard. What each number means, who owns it, the approximate crosswalk, and which one to trust across stores.
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Honeywell vs Levoit air purifiers
Honeywell moves more air per dollar and keeps it simple; Levoit is quieter and smarter. How to size it right, what the filters really cost, and why the box room size lies.
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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Patio misting systems: how to install one
A patio mister cools the air you sit in, but only in dry heat and only if you buy enough pressure. Low, mid, and high pressure compared, the step-by-step install, why nozzles drip and clog, and the hard-water upkeep no product page mentions.
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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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How to improve indoor air quality
The order that actually works for dust, pollen, and pet dander: cut the sources first, ventilate, then filter. What each step costs, the MERV and HEPA choices, humidity control, the carbon monoxide and radon dangers to test for, and the gadgets to skip.
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Should you close vents in unused rooms?
It seems like closing the vent in an unused room should save money, but it does not, and closing several can freeze the coil, crack a heat exchanger, and push more conditioned air out your duct leaks. Why the myth fails, when closing one vent is harmless, closing the door instead, and what actually lowers the bill.
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Why are some rooms hotter or colder than others?
One room runs hot or cold while the rest of the house is fine. The free airflow fixes to try first, the closed-door return-air trap most people miss, the room-load causes from afternoon sun to a room over the garage, and what air balancing, zoning, and a mini-split cost.
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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.