whether you replace this old boiler and water heater or continue
inefficiently operating it as an antique with a full set of new safe
replacement controls and energy star rated circulating pumps is up to
you.
who: i'm not the hvac expert for this.
what: is the combustion efficiency of your model number? maybe 50-60
percent?
where you live, the climate: what is the energy source of least expense
for this heating task in your city?
when: you need to do this is either at the hvac company's convenience
instead of rushing the job, while you monitor the pressure and leakage
problems and get a headache, or as soon as you shake some money out of
your budget for this home improvement.
why: for year-round comfort and energy savings.
how: keep doing the homework.
is it still true that there are no high efficiency boilers for oil,
only natural gas?
can you install central air and an efficient gas furnace? nice central
air conditioning may be the wonderful summer benefit that awaits you.
the new insulation package you install into your home will affect your
btu calculations.
see:
http://www.buildingscience.com/resources/