How I can calculate or find a value for the start-up cost of a natural gas boiler? The boiler will have a capacity of about 700 kW and is intended for heating the water for a greenhouse.
For accurate cost estimation you will need to find a vendor and have them supply you a "budgetary quote" for your 700 kW boiler. The vendor can usually get this type of quote to you more quickly than a firm quote because they are not held to that price or terms; though I find that frequently the price is the same when we go to purchase.
When I need an estimate in the next 10 minutes I try to find something on the internet with a price that I can scale. I find a unit closest to the type and capacity I need. Usually economy of scale ensures that I over estimate, but it doesnt hurt to give yourself some safety factor.
574,000 BTU Boiler for 14,000USD
700 kW is 2,390,000 BTU
2,390,000 BTU / 574,000 BTU = 4.16
4.16 * 14,000 USD = 58,240 USD
58,240 USD * 1.2 safety factor = 70,000 USD
Obviously you will have to do this for all your major components, piping, etc.
For installation costs you typically estimate some number of labor hours and multiply by your "shop rate." Accounting should be able to give you this number as it factors in all employee costs like benefits, vacation, training, tool overhead costs, etc.