That said to be sure the best way is to have a heatloss calculation carried out. I posted a UK based HL calculator in an alternate thread you may be able to use that yourself to give you some idea.
In the Uk traditionally heat sizing was carried out with a Mears calculator and this oversized by 25%. If it is the same in the US then the 140,000 might be ok.
So initially I would use a rule of thumb to proviso a boiler size and cost if the client was happy then I would spend the time measuring the rooms, window doors construction and then asses the heatloss calculation.
If the boiler you are having is a fully modulating boiler, then you don't need to worry as much if it is oversized as it will modulate to suit the heat load.
Here it is not uncommon to fit a 35kW combi gas boiler into a duplex apartment because the the higher KW is for hot water flow and demand not to heat the property which probably only required 8kwW.
It's your money you are spending so find an installer who wants your work and will provide a HL calculation, save him some effort and measure your room height length width and window door type and sizes, insulation levels and floor /ceiling construction.