not sure if you provide advice on air _ we just moved to a new house with a fireplace which works well but I am concerned our baby might be taking in harmful air.

Red Nose has included some information in relation to bush fire smoke, following the recent experiences in Australia over summer.
When considering a baby’s exposure of any form of smoke, we recognise that the greater the exposure, the greater the risk.
While any exposure from a home wood fire smoke would be much less than that of daily exposure to bush fire smoke, some of the information may be helpful.

Bushfire smoke contains toxic gases such as carbon monoxide and nitrogen oxides, and particles, all of which can be hazardous.
Small particles in smoke can effects the lungs’ ability to breath normally, aggravate asthma or other respiratory conditions, and can cause a sore throat, runny nose or coughing.
For healthy adults, these symptoms usually go away once the smoke has subsided.
Pregnant women, young children and infants are more sensitive to the effects of breathing in the smoke.

However, we do know that bushfire smoke is toxic, so Red Nose recommends that pregnant women and young children, especially infants, actively limit exposure to the smoke to protect against the ill-effects of the hazardous air.
https://rednose.org.au/article/bushfire-smoke-and-the-risk-of-sids-and-stillbirth

As the exposure to the baby of smoke from home heating would be minimal, the risk to a normal, well & healthy baby would be minimal.
As with all types of smoke, the greater the exposure the greater the risk.
With most forms of heating, (partic wood fire &/or gas) it is important that the room is ventilated to reduce the risk to everyone, but especially baby.
FYI - http://www.environment.gov.au/resource/woodheaters-and-woodsmoke