Would there be black soot on the inside of the windows if carbon monoxide were present? We have a new furnace.

If it is gas the answer is no. For every 100,000 btu's burnered you create 1 gallon of water. Hopefully all goes up the chimney. If spillage occurs the moisture will be on the inside of the home. Get a good CO detector to be safe.

Soot on the windows means that your gas is not burning completely, and since it is collecting on the windows I have to say that you do have carbondioxide in your home.

Since your furnace is new it almost has to do with the venting system, unless the furnace was not installed correctly.

In the city I live in the fire depaartment will make a carbon monoxide test for free at your home and unlike having your own alarm they will search you house and try to find out where it is coming into the house.