Circulator Replacement and Size

Lynnwill

I need the help of some experts with real world experience!!

The house is about 2900 sqft. The 6 yr old gas Burnham boiler is 134MBH output (DOE). It is about 30% oversized for the 105MBH heat loss calc but 5% undersized for the connected indirect water heater. No questions there. The house was built in 1930 and was apparently originally gravity fed. There are 2” mains leading to smaller feeders to a total of 23 cast iron radiators. The total calculated EDR is 1050. The boiler is located in the basement of the two story above grade house. The first floor ceiling is at 9ft – probably safe to assume 15ft vertical worst case from the basement for 2nd floor piping, 4 feet vertical to the 1st floor and as stated 2” and 1-1/2” steel mains in the basement. The length of 2” basement main is about 30 feet. All these dimensions are for supply – same sized returns are however adjacent. Near boiler piping is 1-1/4” copper. The boiler has bypass with a Taco 007’s for the indirect, boiler and a kitchen radiant zone. There is outdoor reset with a Tekmar 260 controller and a relay box connecting the kitchen radiant and main house thermostats to their pumps. The Tekmar is set to 180 max and 140 minimum.
Finally my issue!! I discovered the main house zone is circulated with a Taco 0011. I now realize this explains the velocity noise. Also the boiler never gets to the target temperature since the flow and pump pressure is so high and fast. The Tekmar frequently show targets at 160+ and higher but hangs for a LONG time at about 120+ when the main zone kicks in. You can hear the pump kick in when on the 2nd floor. It takes forever for an in house temperature rise then cold radiators – no real steady comfort.
Question: Which pump is correct - should I change to a Taco 007 or a 0010 pump? Given the likely low head, the choice seems to come down to high flow vs medium flow.
I have read posts that argue for both. Some homeowners have complained of inadequate heating when they went with the 007 – I assume because of the system water volume. At lower head pressure the 0010 flow seems similar to the 0011, probably too high.

Thanks in advance for the help and advice!!!!!

GW

Wow you've got a lot of mass there, can you upgrade to a constant circ Tekmar with indoor feedback? The boiler can't handle the cold stand-by if it's hanging around at 120. If you let things cook for a while, what's your deltaT on sup and ret? I would presume it's quite low. You don't need much pump to move all that water, remember it used to move all by itself in the old days.

Lynnwill

You are correct about the mass. The system was greatly oversized back in 1930. 17 years ago when we bought the house there was a 1960's vintage 330MBH boiler (insane). There has been insulation added in many areas and the steel casement windows replaced with wood double insulated with argon between panes. Obviously the plan in 1930 was to overwhelm the heat loss. It sounds like you believe the Taco 007 would work. Constant circ with indoor feedback - above my pay grade. If you get a chance could you expand. Thanks

Lynnwill

I did not answer your question. Last I measured the Delta-T was about 7 degrees.

GW

Check out my little story on European heating systems.

http://www.wilsonph.com/hvac-tips-pioneer-valley/heating/heating-101/

I think you need constant circulation, keep that water moving. I suspect a 007 will work.

SWEI

You really would benefit from an ODR-controlled mixing valve as Gary suggested. You need roughly 135ºF water on a design day, cooler than that 97.5% of the time. Your boiler wants to see a minimum return temp around there, so you need to mix down.

As to circulators, you'll need about 7.5 GPM at a 25º ΔT to deliver those BTU's. A 005 might work, but you really should consider an ECM smart circ like the Taco VT2218.

Zman

You have 2 posts running on the same subject. Very confusing....

Lynnwill

You are correct I posted the same info twice with essentially the same question - I apologize but never expected that there would be numerous replies in both forums. This will not happen again.

I also have a 007 available. Since I have both available I just tried the 007. I never lose the option to swap in a 0010. The most interesting thing is that the previous velocity noise generated by the 0011 is completely gone. My Delta-T has gone from about 7 to 14 degrees. The various radiators appear evenly warm. What still remains are the very low return temperatures. This forum has opened my eyes to MANY ways for possible improvement - constant circulation, mixing valves, Tekmar reset temperature control, no setback and others. I wish one of you guys was near Philadelphia! I will be identifying a local expert (somehow) and investigating these options. THANKS!!

wmtandson

I currently have a Weil mclain 3 section hot water system with 6 zones.I installed a 504 and a 700 with outdoor reset.

would mine be considered constant circulation?

GW

The fact that you have multiple zones is not necessarily ideal- in a perfect world you would consider having one smart zone (indoor feedback) and TRV heads throughout, on all your rads. I am rusty with my tekmar numbers, those numbers you mentioned does not ring a bell. It seems like you need a mixing vale as already pointed out on one of these two posts.

Steve Thompson (Taco)

Lynnwill, I posed this on your other post - don't know if you saw it...

Sounds like a classic case of over pumping. The right velocity through the boiler will allow the BTU's from the boiler to get on the BTU "train" (thanks Dan). Too high a velocity the BTU's have a tough time getting on (AKA low delta T and cycling boilers). The right velocity in the system is equally as important - the BTU train needs to go slow enough to all the BTU's to get off (AKA - heat the space).

Assuming you have a "typical" system (if there is such a thing), @ 20 deg delta T a boiler with 135,000 BTU OUTPUT needs 13.5 USGPM. As far as head goes, again too much is not a good thing - it will cause over pumping by moving the intersection of the system and pump curve out to the right resulting in excessive flow.

Unless you have very long runs, extremely small pipe or a very high head loss boiler heat exchanger 10 to 15' friction loss is what you should expect (unless of course there are unseen restrictions like semi plugged y strainers, partially open check valves etc.).

It makes perfect sense the system heated better and the noise went down when you used a smaller circ. Too small will show up as noise, low delta T's across the boiler, low return temps (as result of the BTU train going too slow).

Lynnwill

Constant circulation makes a lot of sense in my situation. I have posted an issue in the Controls forum regarding this. I think I have been placed on the correct track. Thanks to all for the help!!