I have a 1954 AA-130 - still kick'n... looks brand new! Down-time is the enemy, so running it for DHW over summer time, if possible, may cost a few dollars extra a month (currently) but you'll be maintaining a boiler that will outlast you! 40 years of boiling sounds better than 20 years... and if running 24/7, 365.25 days a year gives me 40 years over 20... it's worth the extra $.
I live in Central Pa, so coal is not expensive here. Even at 20lbs a day, I'd pay about 10 bucks more a month for about 6 months to keep my boiler 40 years as opposed to 20. 60 dollars a year for twenty years... even at a 4% avg. rate of inflation, you'll only spend a bit more than 1700 dollars over the CURRENT rate of electricity. We all know that is going to change... So, BURN BABY BURN! In the long run, you are much better off.
I'll be burning through the summer if I can maintain a draft!