If you plan on having internal combustion engines of any sort in the garage below, don't skimp on air sealing the garage ceiling and walls {this is where closed cell spray foam insulation is very useful}.

At minimum you will pay for a new boiler sized sufficiently to heat the space for the smaller unit, assuming the existing boiler will heat the larger unit.Then you might need to have more of a combustion air supply in order to support the additional burners.

Gas flue isn't sloped correctly for combustion air to exhaust properly Remove debris from ductwork (brick/ mirror chucks, etc. seen when vents were removed) which prevented air from circulating.

(Not in order)1) Check and Replace Smoke Alarms every 6 months2) No 100 Watt Light Blubs allowed3) No Daisy Chain of surge protectors, max of 6 items per wall outlet which has usually has two.4) Keep candles in a sturdy holder on a level surface, away from combustible materials and out of the reach of children or pets.

I had a similar experience ...I received a letter from the county about a code violation for combustible materials stored in an unssafe manner.Since this property is in the mountains in a national forest, these things are taken very seriously.

or right before that crazy 20% interest rates.. or the deep recession of the 70s/   then you had the late 90s dot com bust which effected some markets.. then of course the mother of them all the GFC  caused by CRA and sub prime lending... and over exuberance in real estate in General... that if anything would be the only thing I see as common thread over exuberance and everybody and their brother gets into it with many not qualified or experienced enough then they cut and run like they were dumping a bad stock.Just my thoughts.. curious on yours. 

You'll probably also need a smoke detector in the hallway (and possibly in the bedroom) and a CO detector in the hallway if there are any combustion sources in the house (and sometimes regardless)

When he said it's the exhaust fan, I assume he means the little fan that clears the vent of combustible gases before the ignition kicks on the burners.

I remember taking an environmental science class decades ago and the Prof was like these combustion engines are basically 100 year old designs that are half heaters just wasting energy.

Those who understood the underlying technology and value in companies made money.I am just saying that to read only the headline news and to believe the generalities of a few articles is akin to "the sky is falling" mentality of the ".com" bust.