Hot Water Loop off Boiler - Qs re Circulator Level

VeniVidiVenti

Hello all. This is my first post here. Like I'm sure many have said before me, I wish I would've found this place BEFORE I sunk thousands into my steam heating system.

I am glad to be here now though and hopefully with your help I can get my single pipe steam system operating properly. In due course I'll put up some pictures with some questions about the system as a whole, but right now I have a pressing issue and that is:

I recently had my boiler replaced by a large residential / commercial outfit and while the fellas were nice enough there were some things not done, or not done how most folks on this board would have done it (i.e. copper risers, elimination of one riser from two on prior boiler, etc.).

But the issue pressing right now is that the water level in the new boiler is lower than the previous one, and I believe this means that the circulators running a baseboard loop and water heater (two circs) are not far enough below the water line to prevent cavitation. Essentially, the first time the water level got down far enough to call for make up water (after almost a full season), the pump started making tremendous noise and died in short order. I come to this conclusion mainly from reading a few different threads and articles on this site. The installer is coming by tomorrow to check it out.

I'd say the water line on the new boiler is 6-8" below the prior. I've marked it poorly with a sharpie on this side of the boiler. The pump is now just below the water line, where it used to be 10" or more. The ball valve pictures was on the same level as the take-off from the old boiler. The installers piped that up from the takeoff on the new boiler to meet the old piping.

I welcome any thoughts on this. Assuming those circulators should be lower, I am hoping that I can reach an agreement with the installer to lower them, but I'd like some input on either how low, or something to point to to bolster my case.

It's also possible I'm way off here and pump failing was pure coincidence. That pump (Taco 0011 F4) was not new.






Thanks!

VeniVidiVenti

BTW I a referring to Dan's comment in this article to "remember to keep your circulator as low as possible to take advantage of the static weight of the water in the boiler."

https://heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

And in another thread I saw that I can't find right now a poster echoed that, saying they essentially put the pump 'on the ground.'

Jamie Hall

It's not at all uncommon for the new boiler to be set with a lower water line than the old one. That should never happen, of course, but it does. May I say that you are fortunate that it didn't upset the rest of your steam system? it often does, as returns which should be wet become dry...

So be happy about that.

As regards the pump, though, part of the solution is going to be to get it as low as possible. On the floor, in fact. But there is another problem which may not be quite obvious: the suction intake from the boiler always must be below the water line as well, by at least three pipe diameters to the centre line of the intake. Otherwise the intake will suck in air (or steam!) when the pump runs, and that is just as bad. I'm not quite sure how that condition can be met with that boiler sitting at that elevation. Is there a lower tapping that can be used?

Big Ed_4

With a condensate loop , you should use two bottom boiler taps not to air bound the loops and to use the cooler water of the boiler . Also add a boiler bypass mixing valve to temper down the temperature of the loop . To help prevent the low pressure side of the circulator breaking into steam .

VeniVidiVenti

Thank you for the responses.

In case is wasn't clear in my earlier post, the installers installed the boiler ONLY. They just ran pipe to the pre-existing loops for baseboard and hotwater.

Below is another picture. The feed for the baseboard and hot water loops is below the water line. My issue is that they piped UP (in copper) to reach the pumps that were there already. So although the pump is still below the water line, it is much higher (closer) to the water line- say 2-3" where it used to be 10" plus.

That vertical rise from the boiler offtake is 11".

The installer was just here and he said it doesn't matter as long as the circulator is below the water line. They'd like to charge me to change the pump ($400, plus labor, prob. $200 bucks. Plus tax I suppose).

I contend that the change in dimensions here has affected the longevity of the pump, and I want them to change the pump AND lower the whole assembly (free of charge, naturally).

We argued (politely) a bit about it but I have no literature to point to on this. I asked him if he'd take Dan Holohan's word for it (ha!) and his words were "well you have to listen to Dan Holohan. I've MET Dan Holohan," (said with pride).

So here we are and we'll see what they come back with. I've got a new cartridge and I think I could isolate, drain and refill the baseboard loop myself. The cartridge replacement looks trivial on youtube. So I might change the cartridge, and if / when that fails inside of a year call the installer again and leave them a bad review on yelp.

I do welcome any further thoughts on the circulator pump level, and if anyone can make a clearer argument in my favor than I did that would be super helpful. My contention is, based on what I've read here, is that it is insufficient for the circulator pump to be simply below the water line. It must be low enough to raise the water pressure in the pump and prevent cavitation.

Please let me know if I'm wrong on this.

Thanks.

ethicalpaul

I think you are right. The higher the pump goes, the lower the pressure will be at the intake side of the pump.

Tell him that since he's met Dan, he should know to trust his opinion on this. The linked article above talks all about using the static pressure due to the weight of the water in the tank to minimize cavitation and flashing. Here is a particularly apt passage (my emphasis):

Q: Where should I pick up my supply tapping?
A: That will vary from boiler to boiler. Modern steam boilers don't have very many extra tappings. You always want to pick up tappings that are lower than the boiler's water line, of course. And remember to keep your circulator as low as possible to take advantage of the static weight of the water in the boiler.

My hot water circulator is sitting on a board right on the floor, like 3/4" above it (and horizontally oriented). I've never heard it cavitate.

Big Ed_4

I assume the heat loop is upstairs ? How far up ? That 0011 was added to push out air . Where does the loops return ? How do you purge ?

VeniVidiVenti

Thanks again. EthicalPaul - how far below the offtake would you say the pump is (approx)? Are you also circulating up to a ground floor?

Big Ed, the loop is in a ground floor addition, so likely less than 10ft above the boiler water level. It is a bit of a lateral run through the basement and then through an uninsulated crawlspace (pipes are insulated... more or less). I'm not sure there'd be any other way to purge it other than the same way you'd fill it, with a hose until a drain on the return runs without air.

I don't understand this: "That 0011 was added to push out air" This circulator takes hot water from below the water line of the boiler and sends it through the baseboard radiators. My thought is that the circulator isn't low enough, and therefore there is not enough pressure to avoid cavitation.

Jamie Hall

There are several issues here...

@VeniVidiVenti noted, I believe, that the new boiler water line was lower than the old. Also that the intake for the hot water pump was near the boiler water line. And then noted that the first time the water got low in the boiler, the pump made a horrible noise and died.

Which is a very nice description of the pump either sucking in some air (intake too close to the water line) or cavitating on low net positive suction head) pump too high relative to the water line and hot water. And, indeed, the problem could be either or a combination of both. Whatever, the pump was trying to pump a gas rather than solid water, and died.

That needs to be fixed, or it will happen again. The fix is not difficult -- make sure that the intake tapping in the boiler is far enough below the low water cutoff level to be safe (at least three pipe diameters) and that the pump itself is located low enough -- at least a couple of feet or as much as possible -- to keep an adequate positive pressure at the impeller eye to avoid boiling and cavitation.

Now issues with purging the rest of the loop are interesting, but not relevant to the cavitation problem. That said, for many of the smaller pumps ten feet of lift is pushing it pretty hard and thus, while the loop will work if it is once fully purged and without air leaks, it may be hard for the pump to purge it. But -- this introduces another possible gotcha: the outlet must also remain submerged at all times. Hopefully the return connection for the loop is into a wet return before the Hartford Loop, or if not into a fitting right at the bottom of the boiler.

ethicalpaul

My offtake is about a foot from the bottom of my boiler. The boiler is on 4" blocks. The pump is on the ground. So I guess my pump is about 14-16" below the offtake, measured on center of pump.

My offtake has got to be about a foot below my water line. If you want to see, it's the indirect water heater port that is supplied on Peerless 63 boilers (manual available online).

I agree with everything Jamie wrote, especially that you have to separate in your mind the cavitation/air problem from the head problem.

So having said that I will now speak about the head in my system, just because I think our systems are pretty similar.

As I think I mentioned, I too am circulating boiler water directly through my pump and to two radiant floor loops.

One of these loops is on the first floor and one is on the second floor, so they are about 6' and 16' above the pump.

My circulator (The Grundfos 3 speed one) cannot purge the lines itself. I have an Uponor distribution station for the loops and I run a garden hose to it to purge out the air, then once most of the air is out, the pump is able to circulate both loops just fine. I think you said your situation was similar.

Because it's an open system, any bubbles get carried back into the boiler water so it's rather self-clearing of air. Also the two loops are oxygen-barrier pex by Uponor with no fittings at all so I don't expect any air can get into them. I'm not familiar with the 0011 that Ed it mentioning, and I don't know if you have any air trouble in the loops separate from when your pump sucks it in but I just share this info in case it's useful to you. Cheers!

PS: regarding water temperature, I do also have a bypass loop as described in Dan's article above. It works fine, but I had to greatly restrict the flow of boiler water into the system with a valve because even with the bypass valve fully open, the water always seemed to prefer to come from the boiler at 212 degrees. My distribution station has thermometers on each loop so I can slightly adjust the valve from nearly shut all the way to almost nearly shut as needed to get the max temperature where I want it.