I have a boiler for my heat and hot water. My plumber wants to replace the pump on the boiler to a more powerful model that pushes more water through the system which he says will provide more heat. He also wants to rewire the controls to give priority to the water heater over the other heat which should provide almost the same benefit as adding an on-demand water heater. All of that makes sense to me. But he also wants to add a 2nd pump just to the water heater which he claims will push even more hot water to the water heater. But if both pumps are the same capacity, will the 2nd pump really do anything? It seems the 2nd pump will only get as much water as is pushed by the 1st pump, so there would be no benefit to adding that 2nd pump. Am I missing something?

What is the pipe diameter connecting the boiler and indirect WH, both supply and return?

3/4". Also the WH is about 8' from the boiler.

3 speed circulators would be the best option.
look at the grundfos model. on high thy pump like crazy...
you can get them on-line for under a hundred bucks..
as for priority for the water heater.. don't do it.
if something ever happens to that circulator and the water heater is calling, you will have no heat in the house. if this ever happens when you are away, the house could freeze-up if the outside temperature is very cold..
lastly, insulate the feed and return pipes going to the water heater.

Indirect water heater manufacturers have very specific pipe size and flow requirements for their equipment. There are ways of calculating exactly which circulator is required. Certain systems can be over-pumped, and will suffer. Others require over-pumping or the last radiators will not get heat. Knowing more about your system would help.

I have a SuperStor SS-40 water heater. My boiler is a Weil-McLain GV-6. I have 1" manifolds feeding the 5 3/4" piped zones. If I were to do it, the idea is that the bigger boiler pump, prioritized hot water, and the 2nd hot water zone pump would give me almost continuous hot water without the need for an on-demand water heater after my current water heater, where now sometimes I run out. It would also give me more heat through my radiators (from the bigger boiler pump) because of the increased hot water flow.

Are the zones fin-tube baseboard? If you use a Taco ZVC 406-4 w/ priority, it has a protection feature that returns the control to the heating zones when the call for domestic hot water lasts an hour continuously. Evidently, not all versions have that feature, so make sure it's 406-4.



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Just to be clear....he can't just change the circulator in the boiler. The boiler circulators have to be left as is, and everything has to be piped primary/secondary.

Most are, but one zone has 2 in-floor fan-driven radiators along with a few baseboards. And of course one of the zones is the water heater.

I do not know what relay he will use to create the priority but I'm now thinking I would not have him do that. Instead, I'm thinking of having him keep the wiring as is with no priority on the HW, but add the 2nd pump to the water heater line. So when the WH needs heat, that 2nd pump would go on, and pull its capacity through the WH. The upgraded 1st pump in the boiler would supply to the 2nd pump but also to the other zones in the normal way if they needed it. That way if there was ever a problem with anything in the WH loop, that at least the other zones would not be locked out from getting heat.

That 406-4 would certainly work well. I particularly like the 1 hr timeout so that the heat zones are not locked out for more than that time. But I do not think we was going to use that device. I think he was just going to wire in a relay to provide the priority. But I doubt there would be a timeout in case of a failure.

as paul said...DO NOT UPGRADE THE BOILER CIRCULATOR... without written permission from weil-mclain. you will void the warranty..
that boiler circulator is there to keep the boiler from going into melt down. it and its recommended piping are engineered at the factory and if you change things weil-mclain will not be happy.
you can do as you wish with the system circulator/s as long as you follow weil-mclain's piping diagram in the manual..
i'm not great on wiring BUT.. if it were me..(always a dangerous statement)..
i would eliminate the superstor zone valve (3/4 inch with too much restriction) and add the second circulator making it a 3 speed IFC model. so what you would have would be the house zones controled by a system circulator with multiple zone valves. the superstor would have no restrictive zone valve but there would be no flow to it as its circulator has a built in flow check. when the superstor call, the system would fire up as it does normally. a seperate relay would call on the superstor circulator and away you go.. keep the superstor circulator as far away from the boiler piping as possible..

what i'm describing is sort of a hybrid zone valve-flow check mix. it may be the only one in the country??

You guys are adamant about not swapping out the boiler pump. Really, I appreciate your input. The HVAC plumber who was going to do it has been doing these kinds of changes for a few years, so I trusted he knew what he was talking about. But maybe not. So, if I don't change the boiler pump, what about just adding a 2nd aux pump after that one to feed the heat zones and the HW in order to get more flow to all the zones (and hence more heat to the radiators and faster recovery of the water heater)? My original question was if the 2nd pump would matter since the max water flow would be determined by the 1st pump anyway. Or, do I have that wrong? Also, the pump with the check value is a good idea if you were doing the system from scratch but the HW value is already part of the system, so I would not want to change it.

The manual is very clear about the pumps that reside inside the boiler. It also shows you how to do what you want , properly. You create a boiler loop off "closely spaced tees". Your new circs will take what they need from that loop, and will not hurt the boiler. There is diagrams that must be followed exactly in the manual.

Thanks for the info. As they say, when all else fails, read the users manual. It's amazing the good stuff you learn when you do that. I'll tell him that he has to reconfigure my system and add the pumps in the way shown.



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Go to Taco FloPro University. com, and sign up. It's free, and they have tutorials that will teach you how to size a circulator properly, read a pump curve, and anything else heating-related you might be interested in. If you're not interested, I can walk you through sizing it.