Line Sizing Danfoss valves 2 pipe steam

Keith Laird

We do a lot of plan and spec work involving upgrading existing two pipe steam radiators to Danfoss valves. Existing valves are either line sized hand valves, or ancient Johnson, Powers, or Honeywell angle pattern pneumatic valves, which are typically line sized.

Anyway, typically radiators are under 200 square foot EDR. Our ATC vendor is supplying 1/2" thermostatic valves, claiming the line sized ones are too big, and will wear out prematurely. Only problem is, with the small ones, the piping gets ugly, typically having to swing the piping out to get the valves in. This is a vandalism issue, as our client on these jobs is a large city's school district.

Is having an oversized thermostatic valve a life cycle problem?

Steamhead

It Depends

but I doubt line-sizing would be a problem.

Your typical steam heating system was designed to run at about 2 PSI or less on the coldest day of the year. Some larger commercial systems were designed to run at 5 PSI or so. Since no radiator valve has a completely free opening (see the charts in Dan's "The Lost Art of Steam Heating" for more) undersizing them would have caused problems.

Undersizing your Danfoss TRVs will also cause problems. The boiler will have to build more pressure to heat the building, which wastes fuel. The steam velocity thru those too-small valves may be high enough to cause noise. And the higher velocity may wear them out sooner.

The Dead Men sized those radiator supply lines according to the amount of steam each radiator needs. Respect them.

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