Measure the house. Plan the fresh air.

What a scan captures, and what it can’t

• In its favour: Walls, doors, windows and openingsApple’s RoomPlan, which many iPhone scan apps build on, recognizes them, and furniture such as beds and cabinets, on a LiDAR iPhone or iPad Pro.
• Plain fact: One room at a time, up to about 30 by 30 ftApple asks for at least 50 lux of light. Mirrors, glass, very dark surfaces and very high ceilings are hard for it.
• Worth knowing: Check one wall with a tape measureAccuracy varies: one developer on Apple’s forum reported errors of about 15 cm (6 in).
• Worth knowing: It can’t see inside walls, floors or ceilingsJoists, pipes, wires and old ducts don’t show up. An installer checks those on site.
• Plain fact: On Android, measure by hand or with a laserPolycam and magicplan run on Android, but their LiDAR scanning is for iPhone and iPad Pro.

For a ventilation plan, also note

• Plain fact: Who sleeps in each bedroomEach person needs about 17 cfm of outdoor air at night for the 800 ppm goal.
• Plain fact: Where a unit could goAn attic, basement, closet or mechanical room with power, a drain and room to change the filters.
• Plain fact: The outside wallsWhere the fresh-air intake and stale-air exhaust could go, clear of driveways, dryer vents and gas meters.
• Plain fact: The gap under each bedroom doorWith the door shut. It decides whether a room needs a transfer grille.
• Plain fact: Anything that burns fuel, and the range hoodFor the combustion-safety check.
• Plain fact: Photos of the attic, basement and closetsSo an installer can see where small ducts could run.

What HouseExhale adds for installers

• In its favour: Homeowners who have measuredEach bedroom’s typical night against the 800 ppm goal, who sleeps there, the door, and what they already tried.
• In its favour: The airflow each room needs, before the visitFrom this planner: fresh air in for each bedroom and living room, stale air out of the wet rooms, and the daytime minimum.
• In its favour: Proof after the installThe homeowner rechecks the same bedrooms from two weeks after, and keeps your airflow sheet with the results.

Installers: what would make a job like this easier? Tell us.

Doing the install yourself

• Worth knowing: Ask your building department about a permitDucted ventilation is mechanical work, and where the 2021 energy code applies, the installed system must be tested for airflow.
• In its favour: Some makers design from your plans for freeZehnder America quotes a system from uploaded plans, with a plan for each room; it doesn’t install, so you or a contractor do.
• Plain fact: Room units are the simplest to fitA through-wall unit needs a hole, a sealed sleeve and power, but no ducts. 475 sells Lunos kits to homeowners in the US.
• Worth knowing: Have combustion safety checkedIf anything burns gas, oil or wood, a change in how air moves through the house can affect how it vents.
• In its favour: Measure the airflow afterwardA flow meter at each grille shows whether each room gets what the plan says. An exhaust-fan meter is about $325, plus a pressure gauge.