Circulator Replacement - Low vs High Flow

Lynnwill

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

The house is about 2900 sqft. The 6 yr old 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!!!!!

Gordy

https://heatinghelp.com/systems-help-center/sizing-circulators-for-old-gravity-hot-water-systems/

Read this article by Steamhead. It gives some insight to over pumping on a gravity system.

Lynnwill

Fantastic reading!! I think I will change the Taco 0011 (completely wrong) to a Taco 007

Steamhead

I wouldn't use the 007- it's small enough, given 1050 square feet of radiation, that you might not get enough circulation at the very ends of the system. That happened to me when I tried a B&G NRF-9F/LW on my system which has 550 square feet. I currently use a Grundfos UP-15-42F.

On your system, if I were using Taco I'd go with the 0010. It has a flatter performance curve than the 0011, making it much better suited to your system. But the Bell & Gossett NRF-33 and the Grundfos UP-26-64F are slightly smaller than the 0010 and would match your system a bit more closely.

Lynnwill

My concern is that the flow is so fast at 25+gpm that there is insufficient opportunity for heat transfer within the boiler. This seems to somewhat explain the slow temperature rise and small Delta-T within the current setup. The 0010 has lower head but the flow rate appears very close to the 0011 in a gravity system (3.5 head).

Thanks for your advice - much appreciated!

Gordy

As steamhead said the 007 is a touch small.

Zman

I think the conversation about the appropriate circulator sizing is right on. This however has nothing to do with the problem you are having with the low boiler temps.

The boiler (assuming it is cast iron) should not see sustained water temps that low. You need boiler protection piping or controls to solve that problem. It has nothing to do with the flow rates and everything to do with thermal equilibrium.

There is no such thing as a boiler being undersized to the Indirect. This is a common misconception. if the indirect is meeting the needs of the house it is not undersized.

Carl

Steamhead

What model is that Burnham?

Snowmelt

You can always go with a variable speed 008 do you know how to read a pump curve, do you know how to figure out g.p.m or head loss, with out those two things your only guessing.

Lynnwill

The Burnham is a Series-2,164MBH input, 134 DOE net. I agree with the comments regarding the water heater. Specifically I was referring to the manufacturers ratings with 180 degree water. It is an Alliance (Burnham AL53L, min 8gpm, 4.5 head@146MBH). It was supplied by a Taco 0010 which I changed to a 007.

I am able to read the curves. I assume a 3.5ft head and 10gpm for 20 degree delta-t. This is based on a 105MBH heat loss calc - 13.5 gpm if I use the boiler output. This is why I am trying to fully understand the allowable 25+ gpm recommendation. I will take a look at the variable 008.

Please do not hesitate to correct me. I know enough to "be dangerous" but fully appreciate your help and experience.

Lynnwill

The variable 008 seems designed for higher head situations than that likely to be encountered in my converted gravity system.

Zman

Right now your boiler is condensing. That damages the boiler and flue. Slowing down the water to the radiators will probably make the radiators perform better and make the problem worse.
Your high mass system will always be slow to react. That is the nature of it.
The best thing to do is to correct the condensation problem using something like a Taco I valve then run your system on constant circ using the circs recommended above. The I valve will be set to a much lower ODR than your present 140-180.
With this setup the system won't always start with cold water. it will just purr along giving you nice even heat.
Do not setback the t-stat.

Paul48

Thirty feet of 2" pipe and a few fittings makes that reverse return. Pipe it off the far end of the return, back to the boiler.

Snowmelt

Then go with the 007 variable speed pump, taco made it easier and better at the same time. Do you know what your head pressure is? Do you know what your g.p.m. Is?

Steamhead

That boiler should handle the flow rate from the 0010. If I'm reading this right, you already have a 0010 that you took off the indirect zone, right? Won't cost you anything to try it on the main zone.

Lynnwill

In full disclosure 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!!

Snowmelt

Lynn I go to pa once in a while, may I ask where are you located, pa is a pretty big area. The snow is going to keep me inside tomorrow if you want call me.

Steve Thompson (Taco)

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).

Rich_49

Lynn , we occasionally go to Philly . We are about 45 - 60 minutes east of you .

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!!