Relatively tiny pump...

FranklinD

My hot water system, with cast iron radiators, has a 68k btu (water output) boiler. The heat loss of the house (done with slant fin app) is about 65k with a -20 design temp.

What I'm finding is that using the gpm formula I require 6.8 gpm for a 20* delta t. The boiler was installed with a Taco 007. When running, I can hear the water moving through the pipes and radiators (all steel pipe, ranging from 3" to 3/4", 9 radiators total). My near boiler piping was changed with the new boiler to all 1-1/4" copper.

I ended up installing a Bumblebee with the sensors. It ALWAYS ends up running at 6.8 gpm (on the screen). Even on the lowest constant speed setpoint, it's at 6.8-7.2 gpm. I believe there's basically 1 ft or less of head in my system as every pump seems to run wide open. It's a Burnham ESC series boiler.

Are there any smaller pumps out there? The I&O manual specifically warns against over-pumping the boiler and I don't want to do that. I'd also rather not have to throttle the pump with my boiler isolation valves (ball valves).

I looked at the Taco 003 but it looks like it's mainly for hot water recirc systems and has 3/4" ports.

So what does a guy with relatively tiny flow requirements do?

And the system heats WAY faster and more evenly with the Bumblebee at 7 gpm than it did with the 007.

Thanks for any help or thoughts!

Gordy

If your confident in the math and 6.8 gpm is what you need, and the bumble bee is giving that what's the problem?

Solid_Fuel_Man

Thats what I was thinking. If it's working well, and not grossly over pumped. What is the flow requirements of the boiler?

Taylor

Gordy

The faster heating could be that you now have turbulent flow instead of laminar flow that the 007 May have been producing.

Steam head has a piece on here about sizing circs in Gravity systems very good read explaining why over pumping produces poor heating. The bumble bee was not out yet so its not in his selection of circ choices.

That read out on the bee may not be correct either.

FranklinD

The Bumblebee ended up being my choice of last resort since I couldn't find (in my limited period to do so) a pump that went that low.

Am I correct in assuming my setup has basically 1 foot or less of head? I guess that should've been my question.

Two story house, 3" mains that step down 1/2" at each radiator take out until they are 1" (which then feeds the living room radiator at the end of the line, so to speak). Radiator Takeouts are all 3/4" except the living room and kitchen which are 1". Longest total loop (master bedroom) is 40 ft of the 2 mains and 16 or so feet of two 3/4" runouts (so 56 feet total round trip).

I used the Taco website to learn more about head loss, and I'm trying to get as close as I can without hooking up any gauges (which I don't have anyway). I just assumed it must be basically nil since the Bee is rated for 7.5 gpm at 0 head and the display varies between 6.8 and 7.5 or so (as was stated, not likely totally accurate).

I was also curious what other people with such a situation (extremely low head, relatively low flow requirements) have used for pumps since it seems like most of the standard choices flow large amounts at low head.

FranklinD

The manual states the minimum flow requirement for the boiler is zero, minimum return 110, minimum supply 130. Which is another thing I'll address come spring. In the shoulder seasons my water temps rarely hit 100 average, when it's -20 I'll probably be around 140-150. Now that I have a boiler with some actual instrumentation I look forward to seeing.

Gordy

FranklinD said:

The manual states the minimum flow requirement for the boiler is zero, minimum return 110, minimum supply 130. Which is another thing I'll address come spring. In the shoulder seasons my water temps rarely hit 100 average, when it's -20 I'll probably be around 140-150. Now that I have a boiler with some actual instrumentation I look forward to seeing.

How is the boiler piped ?

Again go to systems help, hot water heat, circulators, circulators in Gravity systems good read.