A few years ago, one of our tenants called from our rental house to tell us that they had called 911, because their carbon monoxide (CO) detector had gone off in the house.

By the time I got there, there were trucks from the utility company and fire department, plus an ambulance already crammed into the tiny street. And there were enough flashing lights to open a disco.

They detected no CO, but had shut off the gas line to the house, and we had to have a plumber come to check the water heater and have the furnace serviced before they would turn the gas back on.

When all that was done, the utility company installed a sensor in the garage for 24 hours to monitor the area. Only then did a neighbor happen to come over to tell me that she had seen them warming their car up in the garage before driving off!

There was enough CO in the attached garage to seep into the house where the sensor was to start this whole boondoggle. So ... your advice was absolutely spot on!

— Serge

Thanks, Serge. Some houses share a ventilation system with the garage, which makes it even easier for fumes to get into the house.

Other houses with attached garages have an “indoor” quality door between the garage and the house, rather than an “exterior” door that seals well against the weather (and fumes).

So, it’s not worth the risk. Back out of the garage if you want to warm up your car. Better yet, don’t warm it up. Just drive away gently and let the car warm up while you’re driving. That’s also the fastest way to warm the engine.