SIOUX CITY, Iowa (KCAU) — As the temperatures dip, furnaces will be working overtime which can cause a silent killer to build up.

Carbon monoxide, a colorless, odorless gas is the byproduct of combustion that can build up in spaces that are not properly ventilated and can be deadly in high concentrations.

Small defects in a home’s heating system can lead to dangerous levels of the gas, but having a carbon monoxide can help prevent tragedy.

Earlier this month in Minnesota, a family of seven died from carbon monoxide poisoning.

“So there’s really not a hard and fast location, either a wall or ceiling, but we do recommend that people put them either in or close to their primary sleeping units of their home,” Deputy Fire Marshal Ryan Collins.

Collins adds those who already have detectors should remember to replace them every seven years.