Although I have enjoyed the ease of metric calculation, especially once I got my hands on an electronic calculator, I do find that there is sometimes a perception issue as some metric units are so much larger than their imperial equivalent.
Doing the technical end of domestic heating, I found it preferable to calculate heat losses in btu/hr (British thermal units per hour) rather than kW/hr (kilowatts per hour) as there are 3412 btu to a kW. It makes radiator sizing easier in my opinion.
Atmospheric pressure is 1bar, but 14.7psi again makes small variations more obvious.
I use 10lbs per gallon of water as my rule of thumb, but then I was born in 1951....