As a mechanical Engineer for a large air conditioning manuf.for my test purposes in the lab I make sure my techs take the vacuum down to 50 microns and let it hold for 30 minutes ( these are new systems so the only oil in system is in compressor )but I know on the production floor they are not...
I read your delema if you have a multi level house look at aprox.6 psig per floor also if you have a gas fired boiler make sure it's tubes are clean(heat exchanger)and burner orifices let me know
