Mention “Spare the Air” days and most people in the region will think of still summer days when smog is at its peak and Bay Area public transit agencies allow customers to ride for free.

But Spare the Air continues in winter, too.

This year, the Bay Area Air Quality Management District will announce winter Spare the Air alerts, banning the burning of wood or manufactured logs in fireplaces, wood stoves or pellet stoves. Only fires in gas fireplaces will be permitted.

The only exemption is for people who have no other source of heat in their home.

Winter Spare the Air days will be announced at 2 p.m. the day prior to an alert going into effect, barring fires from midnight to midnight.

Last year in Napa County, the district looked into 43 complaints about violations of the rules and issued 12 warning letters. “That is actually pretty low,” Kristine Roselius, the air district’s public information officer.

In neighboring Sonoma County, residents filed 131 complaints and the agency issued 41 letters.

Marin County’s 391 complaints was the highest in the Bay Area.

Fifty-five letters went out to offenders.

Last winter was a mild one for no-burn days — when an inversion of cold air acts as a cap and traps chimney smoke so it can’t escape into the atmosphere.

Between November 2008 and February 2009 there were only 11 no-burn days, while the average is between 15 to 20 days.

For a first offense, residents get a warning. A second violation comes with a $400 fine, and penalties increase from there.

Those who received a warning or fine last year do not start with a clean slate this season, which has already begun and ends on Feb. 28.

This year the air district has added an educational outreach program targeted at hotels and restaurants, many of which have fireplaces.

Winter Spare the Air Alerts were initiated because one in seven Bay Area residents suffers from a respiratory ailment, according to Roselius.

Spare the Air

To find out if it is a no-burn day

• Visit www.baaqmd.gov

• Call 1-877-4NOBURN

• Sign up for e-mail alerts at www.sparetheair.org

• Sign up for phone alerts by calling 1-800-430-1515

Complaints about violations

• Napa — 43 complaints, 12 letters of warning

• Sonoma — 131 complains, 41 letters;

• Marin — 391 complaints