"Ray" wrote in message
news:s2Eyj.403$Ie2.128@trndny09...
We have a boiler/radiator system in our six-unit apartment building. We
have been flushing it -- I think it might be called "draw down" -- once a
week.

But I get mixed advice on how often we should do this, and how long we
should let it flush each time.

Any guidance welcome.

There is only one accurate method. Get a meter that measure Total Dissolved
Solids and do a test. A meter is in the $275+ range. The one I use is
on the bottom of page 590 at www.mcmaster.com Number 1128T16

Two things you want to do. One is to flush the bottom of the boiler to
remove sediment. The second is to maintain a level of dissolved solids that
is less prone to sludging, yet is not loaded with oxygen.

When blowing down a steam boiler, the general consensus is to open the valve
three times. The first flush gets rid of what is near the valve, but if you
just let it run, much of the deposited solids just stay in place. Closing
the valve quickly stirs up some of the sludge so it can be sucked out.

Some boilers require chemical treatment to keep them in good condition. It
is not possible to give a guideline on how often as that will vary depending
on operating time, the condition of the water supply (hard, soft,, types of
minerals, etc) Tb be 100% certain, you need a boiler chemical guy that can
do the test and give you guidelines.