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Old 01-30-2014, 11:10 AM   #1
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question about increasing recirc pump hp on one loop


Greetings from Ottawa, where winter isn't quite over yet.......

My boss has a hydronic gas-fired system with old style rads for the most part,
and which are working fine, but one loop of the system is thru a coil in a duct serving an added-on living room. The supply temp through that loop is right on the money, about 130 degrees as is the rest of the system. That temp is reflected in the hot rads elsewhere in the big house, which is the way it's been running for years. A little hot to my liking, but beside the point as far as I can see.

When he calls for heat to the living room, the air handler serving his living room ducts kicks in, but the air immediately cools that coil right down so that the delta across it is like 40 degrees, hot water coming in but barely warm coming out. The air coming from his registers in the living room is cool, never able to really warm the room at all. He has given up using this coil because it simply can't throw heat.

My question is this: Is it worth replacing the 1/25 hp Taco serving that loop with something bigger, would we get enough improved flow across that coil to make a difference? And secondly, can anybody tell me if we could just bolt on a slightly stronger pump or will we have to change the flange also? I'm looking for possible solutions for that now, but any info would be hugely appreciated. I don't think that "robbing" the rest of the loops of heat would be a problem, if that would occur I think it would be slight.

The air handler for that room has a rack for a 240 volt coil, but sourcing and running the cable to a new heater would mean huge work as the electrical panels are full and the cable route to the air handler is quite complicated to fish through without trashing major drywall at least.

Any ideas are welcome, my boss is not a happy guy and I'd like to provide assistance any way I can. Ima start looking at other pumps and see if one will just bolt on to the same seal bearing ass'y.


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Old 01-30-2014, 04:16 PM   #2
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question about increasing recirc pump hp on one loop


Sounds like it has a Taco 007. A taco 0010 should mount up with no real problems. but before you change it out. how high is the oil above the boiler. And what is the water pressure in the boiler.

PS: That coil is most likely sized for 180F water temp to provide enough heat.

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Old 01-31-2014, 07:17 AM   #3
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question about increasing recirc pump hp on one loop


I made a mistake, the pump is actually a Bell/Gossett 1/25th, sorry for any time wasted. The boiler currently runs at about 140 degrees and 18 psi hot, which seems to serve the 2 floor 3000 sq ft house just fine except for this coil.

I fear you are right about the coil being designed for 180 input, this coil will always just go cold as soon as there's any real air across it. Increasing the temp doesn't seem to be a workable option, so I was hoping to increase the flow through it.

Problem is, I'm no expert and I don't want to cause pressure/flow problems elsewhere in the system by trying to boost this loop's flow. I see 1/12th hp pumps that would seem to bolt right on, and they aren't huge money, but the last thing I want is to create stress in the system.

I guess I'm asking if a boosted flow will give me any real world increase in heat from the coil. My instinct says yes, but I have no idea if the rise would be significant.

Edit: the coil is in a ceiling duct about 8 ft. above the boiler, 20 feet horizontal away, fed by the pump and 3/4 copper, and blown by a floor mount updraft air handler/aircon, with the return going through another baseboard rad on the 2nd floor. When this coil cools down, so does the baseboard rad up the line. It cools down about 10 seconds after the air hits it. I don't know now if reducing the airflow is an option, I don't see anywhere that it's a two speed fan, but I'm not sure what to look for.

Last edited by ChantryOntario; 01-31-2014 at 07:23 AM.
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Old 01-31-2014, 10:48 AM   #4
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question about increasing recirc pump hp on one loop


Ayuh,.... Is this a condensing boiler,..??

Most all of the systems I've worked on, run much better at 180, with the return water at atleast 140 to Avoid condensation within the boiler,...

On the radiant heatin' system I put in my rental, I hada put a mixin' valve in the feed to reduce the temps goin' out to the tubin',...
The floor heat seems to like 150,...

It splits at the hydraulic separator I built, so the boiler's water, 'n the return water is Always above the magic 140,...

I've never seen baseboard radiation that worked very well with such low temp water,...

I guess my bottom line point is,...
Bump up the hi-limit to 180, 'n see if it works Better,...
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Old 01-31-2014, 12:29 PM   #5
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question about increasing recirc pump hp on one loop


There's only one baseboard rad in the house, all the other 15 or so rads are big old 200 pounders from the 30's. They work like a charm, and they are quite hot as is the house, even when the water is about 140...I think that 180 degree rads in this house would boil the man out, and the rads are really hot to the touch now. I just need to get this one duct coil to have more water flow so it doesn't cool right down when the blower comes on.

This man is from a tropical climate, and likes the house at about 85 degrees. Try working there for a morning... PHEW!!!!

By the way, the baseboard rad is downstream sharing a loop with this duct coil as far as i can see, and it is hot until the blower kicks in for the living room, then all the heat leaves that coil, goes to the baseboard rad cool, and it returns to the main return at about 100 degrees. Need to boost that one loop somehow without increasing the temps across the board.
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Old 01-31-2014, 06:02 PM   #6
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question about increasing recirc pump hp on one loop


Taco 0010. I think a 0014 would be a bit too much.

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