water treatment for HW boilers


Old 04-20-13, 06:26 AM
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water treatment for HW boilers

A heating contractor I trust is recommending to me a filtration system for several new small commercial condensing hot water boilers (350K btw/hr each) powering a pair of 100 year old apartment buildings with cast iron radiators. What he told me is that he has found that 'mud' in the water in these old systems tends to coat the inside of heat exchangers, causing hot spots, and early failure. He's found that the newer stainless steel HXs are more easily damaged by getting coated by solids in the water. He tests for total dissolved solids (TSDs) and recommends a bag filtration system if the TSDs are high. He would pipe this in the main building runs so that part of the return is always going through the filter. The filter would be changes frequently at first, then less often as the water clears up.

This makes complete sense to me, but I'm wondering what others think, or if there is anything more than just anecdotal evidence about this? I've heard of filtration for steam boilers but not for hydronic. And, I live in an old house with cast iron radiators, and should I think about TSD for my HW boiler?

Also, what other water treatment should we think about? pH?

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Old 04-20-13, 09:09 AM
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Filtration can't remove dissolved solids, only suspended solids. Can you post a link to the filters being recommended? Before following the local contractor's suggestion, I would check directly with the boiler manufacturer.
Old 04-21-13, 06:04 AM
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Good point - should have written Total Suspended Solids (TSS), not TDS. he describes it as the 'mud' you see in old systems like this. The quote says "bag filtration system", and from talking to him, this would be side stream.

From looking around the web, filtration is often used in cooling tower systems where there are much more TSS. One of the reasons you filter TSS in that situation is to reduce buildup on the HXs.

The heating contractor described working through a problem building with Triangle Tube, where boilers were failing prematurely. TT diagnosed this as from buildup on the boiler HX from high TSS, causing the HX to fail.
Old 04-21-13, 08:29 AM
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A prerequisite to ANY filtration system would be a THOROUGH 'flush' of the system prior to boiler installation. Is that included in the quote? I would guess that one could get maybe 90% of the initial buildup of 'mud' out this way at the beginning...

Injecting AIR into the flushing water would create turbulence and help to loosen deposits.

I would probably recommend a 'conditioner' be added to the system water to prevent further corrosion after the fact.

A 'wye' strainer directly in the flow, NOT sidestream', is also recommended to catch the 'big chunks'.

image courtesy pexsupply.com

WYE Strainers at PexSupply.com

Have a ball valve installed on the 'blow down' port to flush without hassle.

Last edited by NJT; 04-21-13 at 09:20 AM.
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