Gravity condensate return

Eric Fendler

I will be replacing a steam boiler for a church. The boiler is used to heat two steam kettles in the kitchen, a water maker, and three tubs of water, apx. 400 gallons each.
The original boiler was very large so there was never a condensate return line installed. The replacement boiler is 400,000 btu's, and I'm sure a condensate return line will be needed. The boiler will only be in use about two months each year, so I hope I can avoid the cost of a receiver and pump and just use a gravity condensate return line. It would be greatly appreciated if someone could help me size the line, and give some advice on the installation.
Thank you very much,
Eric Fendler, Bozeman Montana