need help figuring what size boiler ineed

[rajtyl]

i added 2000sq ft to my existing house .i am trying to figure out what size boiler i need.also ,need to know what is the best boiler to use ,that being a direct vent.i just need it for the 2000sq ft thah i added.also with my old boiler i have a problem with high boiler pressure ,it goes up to 20lb,and sets of pressure relief valve.could this be due to the expansion tank.

[comfortdoc]

Time for a service tech to inspect the existing system. While they are there ask them if someone could come out and perform load calcs for your addition. I'm surprised the building inspectors didn't require plans for heat on an addition of that size.