Indoor air quality in a tight new home: what changes and what to do

Why does a tight house need ventilation?

A tight house needs ventilation because the air exchange an older house got from leaks around windows, doors, and framing no longer happens; moisture from showers, cooking, breathing, and construction materials stays in, and so do odors, combustion gases, and radon. Builders address this with exhaust fans that run to the outdoors and often a mechanical fresh-air system. If those are off, disconnected, or blocked, the house holds whatever is made inside it.

Do the exhaust fans actually go outside?

Every bath fan, the range hood if it is ducted, and the dryer must vent outdoors, and in a new house the way to know is to look: the tissue test at each bath fan grille, a walk in the attic to follow each duct to a roof or wall cap, and a look outside at the caps with the fans running. The bath fan guide and the attic check are the procedures; a duct that ends in the attic is a builder item and a moisture problem in one.

Run the bath fan through every shower and for fifteen to twenty minutes after; a timer switch makes it automatic. Run the hood whenever a burner is on. Clean the hood filter and the dryer vent on their schedules; a clogged exhaust is a closed window.

Is the fresh-air system running?

Find the fresh-air system in the manuals and the mechanical room: a damper and duct to the return side of the furnace with a controller, an exhaust fan set to run on a timer, or a heat-recovery (HRV) or energy-recovery (ERV) ventilator with its own core and filters. Confirm it is on, set as the installer intended, and that its filter or core is clean. Ask the builder at the walkthrough what the system is and how to service it; it is the least understood piece of equipment in most new homes.

How do you manage moisture?

Manage moisture by removing it where it is made (fans) and by keeping indoor humidity in a moderate range: air conditioning or a dehumidifier in humid weather, and a humidifier setting low enough in winter that the windows stay clear. A new house carries construction moisture for a year or more, so expect the first heating season to need more attention. The humidifier guide explains the setting, and condensation on the windows is the signal that it is too high.

• Watch the bottom edges of windows on cold mornings; fog or frost means too much humidity for that temperature.
• Keep closet doors and cabinets on exterior walls slightly open in the first winter so the walls behind them stay warm and dry.
• Check the attic for frost on the roof deck in midwinter; it is house moisture reaching a cold surface.
• Do not store firewood, wet gear, or a large aquarium in a tight house without a plan for the moisture.

Which gases should you test for?

Test for radon once, and alarm for carbon monoxide permanently. Radon comes from the soil under the house, has no smell, and can be higher in a tight house; the radon test is a kit in the lowest lived-in level and the EPA's action level is 4 pCi/L. Carbon monoxide comes from anything that burns fuel and from an attached garage; the CDC's guidance is a detector near every sleeping area, tested monthly, replaced on the manufacturer's schedule, and the detector guide covers it. Both belong on the first-year list.

What should you do in the first year?

In the first year, confirm every exhaust duct terminates outdoors, find and turn on the fresh-air system and learn its filter, keep the humidifier low and the fans running long, run a radon test in the first winter, and confirm the CO detectors are where the CDC says. Report any duct that ends in the attic and any fan that fails the tissue test to the builder in writing during the warranty window. The first-year schedule has the dates; this is the air-quality subset of it.