quick pump question

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Feb 11, 2010
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I'm working out the finishing touches on my plumbing for my OWB and I am stuck at a which pump to use on my main lines. I've determined I need a taco 0013 pump already, so the hard part is figured out. The question is, should I use cast iron or stainless steel? My particular OWB is a semi-closed loop system in that is uses a bladder to keep the net pressure as close to 0 as possible, but no more than a few psi. If it reaches a handful of psi (I'm thinking about 10 IIRC), it vents the pressure off via a relief and then returns to a closed system. Should I use a cast iron pump or a stainless steel pump?

I've found the cast iron 0013's with the IFC for $230/each and a stainless 0013 with the IFC for $465, both of which have free shipping attached to them. I can buy two cast irons for the price of one stainless steel pump, and being the pessimist that I am, I like the idea of keeping an entire spare pump in a box for the day we get 10' of snow and my pump decides to quit working at the same time. But if I'm likely to corrode a cast iron pump in just a year or two, that hardly seems worth it.
 
I believe the rule of thumb is that a cast iron circulator can only be used on a fully closed system. If your system gets any oxygen mixed in you should probably use a SS circulator.

Pat
 
taco has discontinued their bronze pumps and replaced them with stainless steel. you can still buy a few bronze pumps, but they are the same price as stainless.
 
Ouch. I'm sure stainless is better anyway.
 
FWIW I had a cast iron 011 on my OWB open system for 5 years. The OWB developed a leak and I replaced it with a closed system. I doubt I would have made it another year, there was quite a bit of rust inside the pump when I tore it apart. I would assume you will get at least 5 years on a pump with your semi-closed system. I don't know what the life is for a pump in a closed system, but if it's less than 10 years you may be cheaper going with cast iron and planning on a replacement after 5 or 6 years. Just a thought. Of course this assumes the cartridge for an SS pump is pricey relative to the cost of a new pump like the cast iron models.
 
As best as I can tell, the cartridges themselves are all stainless steel regardless of what housing it's in, so a replacement cartridge would cost the same for either cast, bronze, or stainless if I'm correct on that.
 
Our local heating contractor says he prefers to use 007 pumps and when one is not enough he just puts two in series (usually one one on supply side and one on return). That would probably be cheaper than buying 1 0013 and my guess is it would work just as well. Also, just do the cast iron and expect it may need to be replaced twice as often. Once again, it is just cheaper to put in two cast iron pumps over the life of the install than buy one SS...
 
That is an interesting way to put it. I just redid my calculations and I must have made a mistake earlier. I am figuring just about 20 feet of head at 11 GPM. According to Taco:
If any pump is put in series with another pump, the heads are additive at the same flow. To increase the flow, the pumps have to be put in parallel. With pumps in parallel, the flows are additive at the same head. When pumps are put in series, install a nipple between 2 flanges. Bolt the discharge of one pump to one flange, and the suction of the other pump to the other flange.

which means, to use 007 pumps in series, I'd need to put 3 pumps in series to make up an additive ~22 feet of head at 11 GPM. I couldn't put 007 pumps in parallel because it can't pump 20 feet of head. I could use two 0010 pumps in series (but not parallel) to make it work. Two 009 pumps in parallel will just about work too.

However, after redoing my calculations, it looks like I can use the 0011 pump for my entire system (except my DHW side through a flat plate exchanger).

So pricing out stainless circulators, two 009 would cost about $600, two 0010 would cost about $610, and one 0011 would cost about $320. I think I'll go the 0011 route :). If I went cast iron, the 0011 is $200 and $220 with the IFC. I might as well purchase a stainless steel 0011, and if I want a doomsday backup, buy a cast iron for a short term backup.
 
I used a Taco 009 cast iron on a bladder OWB for 9 years, and the prior owner for some time before that. Never a problem, never replaced. When I replace the boiler with my Tarm, took the 009 off and only a mild rust coating on the interior. Keep it as a spare now.

As to circs in series, I have a 007 and a Grundfos 15-58 in series; they have similar flow characteristics. There is only a small gain in gpm with both pumps on. The 15-58 will move about 7 gpm in my system, and when the 007 is added flow increases to 9-10 gpm.

Others know more about circs in series than I do. I strongly doubt a full additive effect, as my experience bears out.
 
Putting 2 of the same circulators in series can't double the flow rate. Once the second one kicks in the flow rate will "try" to double but once the flow rate begins to increase the resistance to flow will also begin to increase. Higher flow will get you increased head that the pumps have to pump against.

The head is proportional to the flow rate to the 1.75 power (don't you just love fractional exponents?). Doubling the flow rate will increase system head by more than 150%.

Two circs get you higher flow rate than one but not double. Just like Jim's experimental measurements showed.
 
While that certainly may be true, the above quoted excerpt I posted it directly from Taco's FAQ section of their website.

Doesn't matter though, I'm going to use a single 0011 pump.
 
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