Introduction
Once the airflow target is set, the next decision is hardware: which fan, hood, or ventilation unit actually delivers that CFM in your house? Equipment choice matters as much as sizing — a correctly sized fan with a terrible sone rating gets switched off, an oversized hood without make-up air creates new problems, and a cheap duct run can erase 30% of a fan’s rated airflow before it reaches the grille.
Start from the number: the Ventilation Calculator converts your room dimensions and target air-change rate into the CFM and m³/h figures you’ll match against equipment nameplates. This guide explains the equipment categories, how to read the specifications that matter, and which features are worth paying for.
Bathroom Exhaust Fans
The workhorse of residential ventilation. Three specifications decide everything:
- Rated CFM: the headline number — match it to your calculated requirement plus one size up for duct losses. Common residential sizes: 50, 80, 110, 150 CFM (≈ 85, 136, 187, 255 m³/h).
- Sone rating: noise level. ≤ 1.5 sones for bathrooms; ≤ 1.0 for continuous duty. This is the spec most buyers ignore and most owners later regret ignoring.
- Test pressure: ratings are measured at a standard static pressure (typically 0.1 in. w.g. / 25 Pa). A fan rated 110 CFM at 0.1 in. w.g. may deliver far less against a restrictive duct — check the performance curve, not just the headline.
Feature tiers worth knowing: basic switched fans ($30–$80); quiet ENERGY STAR models ($90–$250); humidity-sensing or motion-sensing models ($120–$300) that guarantee runtime without relying on memory. For retrofit situations, inline (remote-mount) fans place the motor in the attic or joist bay with only a grille in the ceiling — quieter in the room and one motor can serve multiple grilles. Pricing context is in the cost guide.
Kitchen Range Hoods
Hoods are sized to cooktop output (100 CFM per 10,000 BTU) and categorized by mounting style:
| Type | Typical CFM range | Best for |
|---|---|---|
| Under-cabinet | 200–400 CFM (340–680 m³/h) | Standard electric/gas cooktops |
| Wall-mount chimney | 400–600 CFM (680–1,020 m³/h) | Pro-style gas ranges |
| Island | 400–900 CFM (680–1,530 m³/h) | Island cooktops; need more capture |
| Downdraft | 300–600 CFM (510–1,020 m³/h) | Where overhead mounting is impossible; weaker capture |
| Insert / power pack | 300–1,200 CFM (510–2,040 m³/h) | Custom cabinetry enclosures |
Key selection points: hood width should equal or exceed cooktop width; ducted models vastly outperform ductless (recirculating) ones for moisture and gas combustion byproducts; and above ~400 CFM, plan for make-up air — a code requirement in most jurisdictions that adds cost and complexity. Mounting height follows the manufacturer: typically 24–30 in (61–76 cm) above gas cooktops.
Whole-House Systems: ERVs and HRVs
ERVs (energy recovery ventilators) and HRVs (heat recovery ventilators) provide balanced whole-house ventilation — equal supply and exhaust — while recovering 60–80% of the energy in the exhaust airstream. An HRV transfers heat only; an ERV transfers heat and moisture, making it the usual choice in humid climates.
Sizing follows ASHRAE 62.2 (floor area + bedrooms), not per-room ACH — a 2,000 ft² (186 m²), 3-bedroom home needs about 90 CFM (153 m³/h) continuous. Select a unit rated at or above that at your design static pressure, with a high-speed boost mode for parties or cooking. Look for AHRI certification (verified performance data) and check the unit’s efficacy rating (CFM per watt) — efficient models move the same air for noticeably less electricity. The estimating guide walks through the whole-house sizing workflow.
Ductwork and Terminations
Duct is equipment too — the wrong duct wastes the fan you paid for:
- Rigid metal duct: lowest resistance, best performance. The professional default for bath fans and hoods.
- Semi-rigid aluminum: a workable compromise in tight retrofit cavities.
- Flexible duct: last resort — roughly double the resistance per foot, prone to sagging and kinking. If you must use it, stretch it taut and keep it short.
- Diameter: follow the fan manufacturer’s minimum — typically 4 in (100 mm) for bath fans, 6–8 in (150–200 mm) for hoods. Undersized duct is a permanent performance ceiling.
- Terminations: roof caps and wall vents with backdraft dampers and bird screens. The damper prevents cold-air backflow; the screen keeps out pests. Both need periodic inspection.
Insulate any duct running through unconditioned space — warm exhaust air condensing inside a cold duct drips back through the fan and stains ceilings.
Controls: Timers, Sensors, and Switches
Controls are the cheapest performance upgrade in ventilation because they determine whether the equipment runs at all:
- Countdown timers ($20–$40): the bathroom standard — 20–30 minute overrun after showering, automatic shutoff.
- Humidity sensors ($30–$80 as add-ons): trigger on moisture spikes; ideal for forgetful households and rentals.
- Occupancy sensors with delay: run during occupancy plus a fixed overrun.
- Multi-speed / dehumidistat controls for ERV/HRV: continuous low speed with manual or automatic boost.
- Smart switches: scheduling and remote control; useful for verifying runtime, not a substitute for automatic moisture response.
Reading a Nameplate: A Checklist
Before buying any ventilation equipment, confirm these five lines on the specification sheet:
- Airflow at rated static pressure — CFM or m³/h, and the pressure it was measured at.
- Sone rating — at the speed you’ll actually use.
- Power draw — watts, for operating-cost estimates.
- Minimum duct diameter — your duct plan must meet or exceed it.
- Certifications — ENERGY STAR, HVI (Home Ventilating Institute), or AHRI for ERV/HRV; these verify the numbers are tested, not marketing.
HVI certification is particularly valuable for bath fans and hoods — it means an independent lab verified the CFM and sone claims. The checklist guide turns this into a pre-purchase verification list.
Related Guides
- Ventilation Cost Guide — what each equipment tier costs installed.
- Pro Tips — placement, ducting, and commissioning advice.
- Ventilation Estimating Guide — size the airflow before shopping.
- DIY vs Pro — which installations are safely DIY.
- Ventilation Calculator FAQ — quick answers to the most asked questions.
Frequently Asked Questions
What do HVI and ENERGY STAR certifications mean?
HVI (Home Ventilating Institute) certification means an independent lab tested and verified the fan’s CFM and sone ratings. ENERGY STAR adds efficiency and quietness thresholds. Both protect you from inflated marketing numbers.
Is a humidity-sensing fan worth the extra cost?
Usually yes — roughly $30–$80 more than a basic model, and it guarantees the fan runs when moisture is present without relying on anyone remembering. It’s the most reliable option for rentals and busy households.
Can one inline fan serve two bathrooms?
Yes — a multi-port inline fan mounted remotely can exhaust two (or more) grilles through one motor, with quieter in-room operation. Size the fan for the combined CFM and balance the branches with dampers.
Ducted vs ductless range hood — does it matter?
Enormously. Ducted hoods expel moisture, grease, and combustion byproducts outdoors; ductless (recirculating) hoods only filter grease and odors through charcoal, leaving moisture and CO behind. Ducted is strongly preferred wherever a duct path exists.
How long do exhaust fans last?
Typically 10–15 years for the motor. Grilles yellow and bearings get noisy before total failure — rising noise or falling airflow at the grille are the replacement signals.
Match the Machine to the Math
Equipment selection is where the calculated CFM becomes a purchase: match the airflow to the nameplate at rated pressure, demand a quiet sone rating, verify the duct size, insist on tested certifications, and put the whole thing on an automatic control. Run your target through the Ventilation Calculator, shortlist equipment against the five-point nameplate checklist above, and confirm code requirements with your local authority before installation.
Disclaimer: Equipment guidance is general planning information, not a product endorsement. Performance varies by installation — ductwork, static pressure, and make-up air all affect delivered airflow. Verify requirements with your local building authority and consult a licensed HVAC professional for system design and installation.
