The Building Code, the plumbing Inspector and your home owners policy will always 'hedge' on the Safest approach. Contact the Permit/Building Inspector in your county/township for the correct information. Generally putting in gas/propane/LP tanks a small tank by itself can put put in with one regualtor providing that it is a fixed permanent unit. (NOT SWAPPABLE). This protects you because some tanks don't have the newer OPD valves on them so you only get 80% of the gas the tank can hold on a fill up now because that is what the law permits. If the tank were swappable or a higher capacity tank the licensed plumber is correct in saying you will need a double regulator. Meaning a hi pressure and a low pressure line going to the tank . Most bigger tanks 250 + and up have this feature. Along with pressure relief valves, Freeze Protection and other safety features. With that being said; if your plumber is licensed as a plumber and gasfitter and he intends to keep his credentials and licensure you should do as he instructs. He is ONLY looking out for your best interest. Don't fall into the trap of being penny-wise but POUND FOOLISH. LP gas has 3 times the thermal energy of Natural gas per cu unit; it is nothing to play with....

Hope you don't mind but I'd like to ask about my similar situation. Our service comes into our main panel in the barn. From there it goes to the service panel in our house (not attached to the barn). And we have a standby propane generator that is not yet hooked up to the service panel in the house (under construction). Our new home is in an area with frequent lighting strikes (and we have the scorched trees to prove it). We've had the power company out twice in the last 6 months when the transformer tripped. One of the strikes burned out all the exterior lights on the barn and an overload fuse on the well pump in the house. At the time of the strike, the power to house was actually turned off from the main service panel in the barn. Power was just running from the service to the main panel. I think that getting a whole-house surge protector might help to prevent or at least lessen damage. Do we need a whole-house surge protector for each ... barn service panel, house service panel, and generator? Or just one surge protector? I'm sure out electrician will know what to do but I'd like to get an idea of what we will need so I can budget.

Our standby generator trade partner sells and installs both Kohler and Generac. He prefers the Kohler air cooled, but if the capacity requires a liquid-cooled unit, he likes the Generac better. Most of what we install are 20 kW Kohler units and they've proven to be reliable. If you plan to install a standby generator to run an air conditioner, better ensure it will be capable of starting the unit.

We are having a very similar problem and we're wondering whether you ever found a solution. Our generator is outdoors beside the garage and the fumes appear to be coming through the wall and concentrating in the garage, where the air intake for the furnace blower distributes them throughout the house. The generator is about 12 years old and this didn't happen before recent weeks, when the CO detector started alarming and showing CO levels during a power outage when the generator had been running for several hours. It's the same CO detector we've had for several years. We also bought a brand-new CO detector and it, too, now shows CO levels rising in the house after the generator has been running for some time - even if we crack the garage door 9 inches or so for ventilation.