I bought an old home which still has the original 1920 snowman boiler. I am having that replaced with a modern gas-fired steam boiler and will also have the gas water heater replaced (the previous owners leased it from an appliance company and it's 8 years old). The plumber that I have chosen to replace the boiler has been encouraging me to go for a tankless Rinnai heater. The more reading I do on these, the more hesitant I am. Currently this is a household of 1, possibly 2 in the coming future. I spoke to another plumber who told me that indirect fired water heaters are not manufactured to be used with steam boilers. Plumber #1 says that they are and that he does not know why anyone would make the claim that the manufacturers don't support their use with steam boilers. Plumber #2 was encouraging me to go with a standalone gas water heater (what I have now).
I'm a layperson and would appreciate any words of wisdom from the group here.
Thank you.
PnG
I've seen plenty of successful installations of indirect HW heaters onto steam boilers. The guy who says otherwise probably doesn't know much about steam boilers (or indirects) and is a bit nervous. It's normally done using the hot water reservoir of the boiler rather than the live steam output, but that's not a huge restriction. Since the water is at atmospheric pressure it can become oxygenated during the summer, which can have an impact on pump life, and many prefer to use bronze impellers with indirects married to steam boilers. (During the heating season all of that re-condensed water has very low oxygen content which is why it takes many decades for iron steam plumbing to rust out, though it eventually will.)
http://www.fiainc.com/documents/7-11 Indirect Water Heaters and Steam Boilers.pdf
http://www.comfort-calc.net/steam_indirect_piping.html
Note on page 11(pdf pagination
) of the HTP SuperStor indirect
In a steam boiler, the tank supply must be connected to the boiler well below the minimum water level. A strainer and drain valve should be installed at the boiler for periodic draining of scale and sludge. Banging and steam bound traps will occur if the boiler water supplied to the heat exchanger has steam or is slightly above the low water cut off.
NOTE:
It is possible to use live steam in the heat exchanger of the SuperStor Ultra 80 and 119 residential and commercial models ONLY. Using any other Superstor Ultra model in live steam applications will result in product failure and VOID the warranty
You can definitely get there from here- but don't hire the guy who is clueless about it for the project, eh? In MA you can even get a rebate for installing one on your steam boiler.
Whether it is more efficient for a 1-2 person family to go with a steam-boiler indirect vs. a standalone tank kinda depends, but the total hot water per hour performance is usually quite a bit higher. How much higher depends on the BTU rating of the boiler. During the summer the high standby loss of a high-mass steam boiler eats into efficiency by quite a bit, but during the heating season (when you'd have the 24/7 standby loss already) the combined net efficiency is quite a bit higher than a standalone HW heater.
With any steam heating system that you don't know the history on it's worth going around and fixing all the stuck radiator vents and system vents, which can make a huge difference on heating system performance. Individual thermostatic radiator vents can even allow you to micro-zone 1-pipe steam for not a lot of money. (Some even have wall thermostat options.) By not overheating rooms and better balancing room temps to your liking you can sometimes make real gains in operating efficiency.
But ultimately they are comparatively efficiency systems compared to the state of the art, no matter what the AFUE numbers say (typically 82%, but only in test laboratory.) If the system uses exterior wall stud bays as plumbing chases (common, in 1920s Massachusetts) your system efficiency is even worse, and it may be worth thinking about a different approach if you plan to live there for decades.
