Converting for Steam to Hot water

Sifin

Does anyone know if you could use a steam motorized zone valve in place of a hot water zone valve? I'm quoting a job that has two boilers one hot water the other steam, and a air handler that has a steam coil also. The steam system is a Hoffman type with steam traps. Feed and return lines. The steam boiler has a condensate tank for make up. I would like to install another hot water boiler and convert the steam system to HW. Also replace the current air handler to a more modern type Hydro air multi position unit.

Steamhead

Don't convert it

unless you like living dangerously.



The current Hoffman Vapor system was designed to run on half a pound of steam pressure. If it's currently running higher than that, it's too high.



Hot-water needs at least 12 pounds, more if the building is higher than 2 stories. This much-higher pressure will find every weak point in the piping and radiators and leak all over the place. This tends to attract rabid lawyers.



Even if it doesn't leak, the radiators may be too small to heat the building on hot-water. And, the return lines are probably too small to handle the flow needed for hot-water... etc. etc. etc.... My company does not recommend or perform this type of conversion



If there's no danger of freezing and the AHU coil is big enough, it may be best to run the coil on HW and eliminate the steam zone valve.

Jamie Hall

Why on earth

replace a Hoffman system with hot water?  It would be like trading a Rolls-Royce in for a Yugo.  Just maintain the Hoffman right.  Save money and sleep better.

On the zone valve, though.  If you have to have a motorized zone valve, or any zone valve, on steam, make sure that it's a full port type, either gate or plug.  Reduced port types, which work OK for water, may give some very hard to troubleshoot problems on saturated steam (which is what we're talking here) -- and globe valves are a definite no-no.