calculating proper GPM

rckymtn

Hello,

I have an older cast iron NG boiler, 3 zones, all baseboard (BB) in 3/4 copper. I have one Taco 007 and three Taco Zone Sentry's. I had leaks from really old purge valves that looked like hose bibs with tiny valves that looked to be a manual butterfly to balance and adjust flow.

They were leaking badly so I took them out and soldered in ball purge valves and also installed 1-4 GPM Tacosetters.

My question is how do I determine the proper flow setting? Slantfin says either 1 or 4 GPM on the BB pdf. So is it exactly 1 GPM or if my 007 can't push 4 GPM, use 1 GPM or do I need to do a calculation to get a number that equates to a proper GPM per zone?

I am a home owner not a pro so go easy on me!

Thank You

https://slantfin.com/images/stories/Technical-Literature/ratings_fineline15_r.pdf

https://www.tacocomfort.com/documents/FileLibrary/TacoSetter_Inline_Catalog_100-159.pdf

Jamie Hall

You don't need a calculation. What you do need is to answer the question "am I getting the heat I want out of this zone?". You can start, though, by measuring the difference in temperature between the water going into a zone and the water coming back out. We usually shoot for around a 20 degree difference. Then adjust the flow to try to get there. Too little difference? Try reducing the flow. Too much? Try increasing it. Try to get all the zones more or less the same.

And take your time! If this is baseboard heat, it may take half an hour for a zone to stabilise, so give it that much time.

Once you get things more or less even, then you can start reducing the flow in zones which are getting too warm, or increasing it in ones which are getting too cool. Again, though, take your time. It takes time for things to stabilise.

LRCCBJ

The flowrate for fin tube baseboard is absolutely not critical. If you look at the slantfin charts, you will see that the output from the baseboard is nearly the same whether you flow 1 GPM or 4 GPM.

However, if you flow 1 GPM, the last baseboard on the loop will not have sufficient output as the temperature will drop more than 20° in the loop. You certainly do not need to flow 4 GPM as this would imply that you could DELIVER 40,000 BTUH from the loop with a 20° DT. That would only be possible if you had 80 feet of element in the loop. Highly unlikely.

As Jamie mentioned, look at the difference in temperature from the beginning of the loop to the end of the loop. Anything between 10° and 20° is perfectly acceptable. Personally, I'd shoot for about 15° to keep the last room from declining too far. By some miracle, the designer MIGHT have installed more baseboard in the last rooms and then the effort to get to 15° is not required.

The flow rates on fin tube are all over the place for most installations as the installer hasn't a clue what will occur. Due to the nature of the beast, this largely becomes irrelevant for MOST baseboard systems.

Then there are those that install a loop with 3/4" that is 200 feet in length with 60 feet of element. Now we get into flow rate problems with a Taco 007.

hot_rod

it would be good to know the heatload of each room. Then you could also adjust the supply temperature and maybe save some fuel dollars

Here is a typical output chart for 3/4” fin tube

IMG_1012.jpeg

You will need to let the zones run for a while before measuring the delta. The delta will be large when the system first starts and everything is 68 degrees. As it runs and warms the delta will close up.

Somewhere between 2-3 gpm. 3 gpm give you just over 2 feet per second velocity. Enough to move air along, and also low enough to assure a quiet system.

rckymtn

Thank You for all your replies, I will use my laser thermometer and see if I can get a 15-20 degree drop on the returns. My boiler is set at 180 degrees on the supply, but I don't know how to adjust the supply temperature. I did read that for air removal 1.5 - 2 fps is a good number to shoot for and that equates to around 3 gpm.

I do notice when I turn up the flow to 3 GPM I get allot of noise in the top floor it's a basement and a 1st and 2nd floor, granted this house was built in 1977 and I think they just laid the copper in holes drilled through the floor joists. I have purged it thinking there was air entrapment but it sounds like I can hear the pump and water flowing in the top floor. I am getting good heat through the radiators though.

EBEBRATT-Ed

In general you want around a 20 degree TD across the boiler. If you take the boiler BTU/Hour output and divide that #/10000 that will give you the total GPM you need.

For instance a boiler with an 80,000 btu output/10000=8gpm for your total flow.

In your instance you could probably adjust the flow in each loop to be about the same return temperature with all zones calling for heat. With all balancing valve wide open check the return temps and close the valve with the lowest TD. This will effect the other zones slightly so it is trial and error. Keep adjusting until the temps are close within 5 degrees or so is good enough.

Keep the balancing valves open as much as possible so you don't starve the boiler for water or reduce the flow in the entire system.

Joe Mattiello

count the lineage footage of base board. It’s appropriately 600 btu output per foot. Lineage footage, and line size will tell you how many BTU’s required to satisfy load, and total loop, and diameter will tell the second half of equation head. Once you know , flow and head you can properly size pump.

As always, amp reading is a good indicator of how the pump is performing. If your over amping, pump might be under sized and if your less than nameplate, pump might be trying to overcome to much resistance.
Taco tech support at 401-942-8000 will be a good resource for you. Hopefully this was helpful