Boiler to Forced Air Plumbing Help/Suggestions Needed

Yanche wrote:Good water is water that has the trapped gases removed and a neutral PH.

I recently got a copy of the new AHS manual and it includes a section on conditioning of boiler water. According to the manual the Ph should be adjusted to between 10.5 and 11. It further says that at a Ph below 9.4 pitting will occur.

Yanche, if the 'air scoop' and associated air vent was between the boiler's outlet and the inlet side [low pressure side] of the circulator pump, then I'd agree, that this may work well to remove disolved gasses.

But creating bubbles, running these bubbles through the pump, which increases the pressure and probably forces some bubbles back into solution, THEN putting the 'air scoop' in the system?? This just doesn't add up for me. The bubbles cause cavitation and other issues in a circulator pump.

As for the PH, I've never checked my PH, but I've not seen any corrosion in the piping yet, and most of my house is old enough that it should show corrosion if it is a problem. Do plumbing supply businesses have PH testing kits??

Greg L

I think the bubbles come out on the high side of the pump, you can hear some good poping & banging with uncut impellars when throttled just right. It sounds like hammers.
Usually steam boilers require an amine to raise the pH of the condensate which can be very acidic. I have seen condensate at 4.0 pH when steam boilers are run without water treatment. It will eat the condensate lines but not the boiler in most cases if the feedwater is kept @ 155* or above.
This is a good one because I don't know of anyone that ever treated a domestic boiler. I know I have never treated mine.

LsFarm wrote: Do plumbing supply businesses have PH testing kits??

Greg L

Swimming pool supply houses sell Ph testing material. However many of the testing kits do not have sufficient range to test in the 10 to 11 range because swimming pool levels are typically 7.3 to 7.8. You can also find sources by searching for "water testing". For occasional use testing strips are typically preferred. Hardware stores and home supply stores like Lowes and Home Depot often carry testing kits.

LsFarm wrote:Yanche, if the 'air scoop' and associated air vent was between the boiler's outlet and the inlet side [low pressure side] of the circulator pump, then I'd agree, that this may work well to remove disolved gasses. Greg L

You are right, I must have been asleep when I wrote my "Correct piping ...". My post has been edited to correct it.

LsFarm wrote:Do plumbing supply businesses have PH testing kits?? Greg L

I don't know if they do. My supply house will test well water for free. They want to sell you a conditioning system. They want a water sample in a clean glass jar that's been refrigerated overnight and brought to them still cold. They keep in it in their frig overnight and test it the next day. My well water is pH = 5.7 I measure my boiler water pH with test strips brought home from the chem lab at work. I'm told the swimming pool test kits will work. My Weil McLain cast iron oil boiler manual says, "Boiler water pH 7.0 to 8.5 is recommended." Also says, "Use one (1) pound of trisodium phosphate for every fifty (50) gallons of water content in the boiler" for cleaning. "A small amount of cleaner may be added to adjust the pH up to the proper range of 7.0 to 8.5"

Yanche wrote:My Weil McLain cast iron oil boiler manual says, "Boiler water pH 7.0 to 8.5 is recommended." Also says, "Use one (1) pound of trisodium phosphate for every fifty (50) gallons of water content in the boiler" for cleaning. "A small amount of cleaner may be added to adjust the pH up to the proper range of 7.0 to 8.5"

I think that cast iron is much less susceptible to corrosion and pitting than a steel boiler. Perhaps this explains the difference in the Ph recommendations from Weil McLain and AHS.

Yanche wrote:My well water is pH = 5.7

Wow Yanche that stuff will make the blueberries happy.

I have to wonder just how critical the boiler water is. I think most are filled with well or municipal water just as it comes out of the pipe. I never heard of anyone junking a coal boiler because of structural failure of the boiler because of corrosion from the water. There may be that odd case out there, but I think most stoker boilers are junked because of mechanical breakdown of the stoker or, and probably the most likely reason, the owner is tired of the extra work involved with coal and does not mind paying extra for oil or gas.

Ian, that hammering is one of the damaging effects of bubbles in the system. If there were not bubbles in the water going into the pump causing the hammering, then there are low pressure points on the impeller or impeller housing that with just the right temp, flow and impeller RPM cause bubbles to form and cause the hammering. The impellers have to be very heavy duty to stand up to this.

In aircraft pumps, once cavitation has occured the part is usually replaced, the cavitation or hammering eventually causes pitting or cracking of the impeller.

Greg L

Yanche, I thought you were quoting your boiler instal manual or heating class information, sorry if I sounded argumentative. I guess since I've seen so many systems that are 30+ years old work just fine with the pump on the inlet side of the boiler [cooler water] that I'm a bit stubborn to accept the new ideas.

[you should hear me gripe when the 'whiz-kids' come up with some new cockpit prceedure to 'fix' something that isn't broken]

Greg L

LsFarm wrote:Ian, that hammering is one of the damaging effects of bubbles in the system. If there were not bubbles in the water going into the pump causing the hammering, then there are low pressure points on the impeller or impeller housing that with just the right temp, flow and impeller RPM cause bubbles to form and cause the hammering. The impellers have to be very heavy duty to stand up to this.

In aircraft pumps, once cavitation has occured the part is usually replaced, the cavitation or hammering eventually causes pitting or cracking of the impeller.

Greg L

I know, we just remaned some 13" 60 HP Goulds pumps on my Ultrafilters. You would not believe the pits in the 316 S/S impellers. It looked like someone worked it over with a prick punch on a jackhammer. And these pumps did not make any noise, so you can imagine the damage that is going on if they are banging loud enough to hear.

Water treatment is critical in steam boilers as the loses in the system are much higher than a hot water boiler. The large amounts of additional makeup water always brings in fresh Oxygen and dissolved solids along with salts and sediment. This is why steam boilers must be blown down daily and drained and cleaned yearly. The sediment will build up and eventually destroy the steel because of the heat. Home boilers use extremely small amounts of makeup water so the treatment is not a real big issue. It probably should be, but most people just don't bother.

Coaledsweat my have something about coal boiler temperature overshoot on shut down. My AHS does overshoot some but no where near the pumps upper 240 degree upper spec limit. The pump is more that two feed away from the boiler and there is no way non flow heat conduction in the piping could get it that hot. In my HVAC classes I was told pumps historically were on the return side because they couldn't take the heat. Clearly either location will work.

My piping is such that my coal and oil boiler are in series. When I first add water the pH is 5.7 or a little higher. Over time it will increase without any base element added. I've been told the cast iron manufacturing process leaves elements in the casting which over time will raise the pH of the boiler water. That's been my experience but the effect is less pronounced now that I've drained and filled my system any number of times.

I think much of the literature about boiler water pH comes from industrial sizes boilers making steam. It's not clear to me that it applies to residential hydronic use. I've never seen any damage done to residential hydronic boilers, pumps or iron pipes caused by any value of pH. Now my pH = 5.7 water will eat through copper pipes in about 5-7 years. But it only occurs on copper pipes that have new well water constantly going through them. I've had to change all the piping in my house to PVC or CPVC. I've had the bottom of the line electric hot waters fail in less than the 3 year warranty. After the third free replacement one manufacturer's rep directed the supply house to give my my money back to end their warranty obligation. That's when I went to a stainless steel indirect heater. I've also tried two types of acid neutralizing systems, limestone pellets and base fluid injection. Both were high maintenance. The best solution for me was plastic pipe, stainless steel tanks and faucets what are plastic on the inside with ceramic valves.

I would say you have some serious well water at 5.7 pH, that water is going to be hungry for anything it can get.

I agree that a sealed system is best but I would put in an automatic fill valve in and a one-way check valve and leave the supply line open. In case of a leak your boiler could become a serious pressure cooker if there is no automatic fill. Normally boilers have a low water cutoff but with coal you can't just shut off the heat like you can with an oil burner. A new problem has come up to which I don't think I have a good solution. The heat exchanger coil has copper tubes coming out of it, the boiler supply and return lines are steel pipe. I'm afraid that the connections will leak due to the different expansion rates and there is the problem of dis-similar metals rotting out the pipe. What I'm going to try is to connect the copper to the steel via brass gate valves and see how it works.

e.alleg wrote: Normally boilers have a low water cutoff but with coal you can't just shut off the heat like you can with an oil burner.

A new problem has come up, I'm afraid that the connections will leak due to the different expansion rates and there is the problem of dis-similar metals rotting out the pipe. What I'm going to try is to connect the copper to the steel via brass gate valves and see how it works.

Do you have a steam boiler? I never saw a hot water boiler with a low water cutoff.

Use a good pipe dope and/or teflon tape, you should not experiance any leaks.