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Draw down boiler? ? ? Ray 03-02-2008
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Posted by Ray on March 2, 2008, 3:24 pm
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.




Posted by Edwin Pawlowski on March 2, 2008, 5:38 pm

> 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.



Posted by Ray on March 2, 2008, 7:11 pm
Thanks -- that's very helpful.

>
>> 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.
>



Posted by beecrofter on March 3, 2008, 10:39 am
> We have a boiler/radiator system in our six-unit apartment building. We ha=
ve
> 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.

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
decent blowdown.
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.

Posted by Clot on March 4, 2008, 6:34 pm
Ray wrote:
> 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.

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/
lumber?
http://www.gasapplianceguide.co.uk/central_heating_systems.htm

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.



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