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.
The idea is so that you don't sludge up the system and/or stop the low
water cutout from shutting things down if water level drops.
On a boiler that size I bet you would pull about 2 gallons for a
During the heating season if it was my boiler I would look twice a
week and put an x on the calandar so it doesn't get forgotten.
Living the other side of The Pond and reading this site quite frequently,
I;m under the impression that central heating systems on the Left Side are
usually different to those we use.
Do you mean this sort of system powered by gas, oil or solid fuel - coal/
If so, then frequent bleeding could assist rusting! It would draw in fresh
oxygenated water. What is common for such a system here is to add an
inhibitor to a new system to prevent corrosion and sludge build up and then
drain every few years. We can purchase fluids here to help flush the system
for this process, then wash through with fresh water, then refill adding
inhibitor, (the cost of the process from recollection is circa $40,
excluding my time of about two to three hours).
My current system that I have had from new in a new build house has been up
for almost 25 years and I've flushed it just 3 times in that time - if my
memory serves me well! No leaks, no problems apart from assisting the
circulatory pump to wake up in The Fall some years.
That is the beauty of steam. Water needs a pump to push it and if you have
a large building, you need a large pump with high pressure. With steam, the
pressure of the steam will move it up and the condensate is either gravity
returned or pushed by the steam pressure. Some have a single pipe that
handles both steam and condensate.
Steam under pressure carries a lot of energy with it and it can go long
distances with minimal loss.
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