Venturi monoflow circ pump

alboguy · January 21

Hello I have a venturi monoflow system, weil mclein gold oil fired boiler, feeding 8 recessed cast iron radiators. The pump is a taco 007 f5. Aquastat is set at 180 degrees with an 8 degree fixed differential. All the radiators heat up nicely but the system cycles a couple times to reach let's say 1 or 2 degres when set. Would a bigger circulator make a difference, or a aquastat with a hihlgher degree offset let's say 15 degrees. Iam just trying to make the system more efficient. Thanks.

mattmia2 · January 21

Figure out how big the radiators are and how much they can output at 180. taking the temp of the supply and return to a radiator will give you some idea too. it is likely that the boiler is way oversized rather than there isn't enough flow in the emitters.

EdTheHeaterMan · January 21

A couple of things.
1. What is this flange connected to?

2. Can you show a photograph of a Monoflo® tee. I do not see any in the photos you posted.
3. Are there any zone valves in your system? There is an extra transformer, that is why I asked
4. I see a circulator pump on the return. Is that the only circulator pump?

alboguy · January 21

1- that is the supply I guess, this is a 1 zone with thermostat located in hallway, that is the only circ pupm

EdTheHeaterMan · January 21

Thanks for the added photos, you do have a one pipe Monoflo or venturi tee system. Are there two branches?

It appears that you have a boiler that can fire at 1.25 GPH with a NET output of 131,000 BTUh. It also appears that the return pipe is 1" Copper Tubing. Just so you know there is a rule of thumb that states that 1" copper pipe has the capacity to move 80,000 BTUh.

Have you ever heard "You can't put 10 pounds of potatoes in a 5 pound sack"? You have a boiler with 131,000 pounds of potatoes and you only have a 80,000 pound sack toi move that heat with. So the boiler overheats and reaches the high limit temperature before the thermostat is satisfied. then the burner stops but the circulator is still heating the radiators. after a short few minutes the water temperature drops to the cut in differential temperature and the burner starts. If you actually clock the burner run time in any given half hour of constant operation. (you would need the let the home temperature drop to maybe 60° then set the thermostat to 80° and then use a stop watch to time the on off cycles.) At the end of 30 minutes you may find that the burner operated for 18 minutes out of 30 minutes. This will indicate that your boiler is about 30% larger than the pipes can handle. If the burner runs for 15 minutes out of 30 minutes, then your boiler is 50% oversized (or twice as big as it needs to be).

The only way to get longer operating cycles is to fire that boiler with a smaller nozzle. Perhaps a 1.00 GPH firing rate or even 0.95 GPH firing rate. This must be done by a professional with knowledge of oil heat combustion and has the tools and instruments to check the stack temperature, draft, carbon dioxide, oxygen, excess air and smoke, to be sure it is not under-fired, which can cause premature boiler failure.

You may not be able to down-fire that boiler to 0.95 GPH You may only be able to go as low as 1.05 GPH. that is why you need the combustion analysis tools. By firing the boiler at say 1.05 GPH the boiler will end ups with a lower NET output by about 15%. if you make the boiler 15% smaller, then your on time will increase and you may even get the off cycle to be a little shorter.

alboguy · January 21

House is 1500 sqf, the pipes run throughout the basement and then throughout the garage, how do I check if 2 branches? The burner ran now for 35 min to get up 1 degree

mattmia2 · January 21

EdTheHeaterMan said:

It appears that you have a boiler that can fire at 1.25 GPH with a NET output of 131,000 BTUh. It also appears that the return pipe is 1" Copper Tubing. Just so you know there is a rule of thumb that states that 1" copper pipe has the capacity to move 80,000 BTUh.

There are also only 8 radiators. A 10,000 btu/hr radiator would be a pretty big radiator so it is unlikely the radiators can get rid of 80,000 btu/hr. Basically the boiler is likely twice the size it should be.

You could change the aquastat to one with an adjustable differential as well as downfiring the boiler as far as Weil recommends.

EBEBRATT-Ed · January 21

The differential on the aqaustat is too small.

Set the high limit at 190 this will give you 180 average at the heating units . At 180 your only going to get 170 average temp not enough in cold weather,

An 8 degree differential is going to make the burner cycle. What you want is the burner to come on fire for 15-20 min then go off and sta off for a while

alboguy · January 21

Which aquastat should I get?, my water heater is electric.

HVACNUT · January 22

Is the boiler a GO-4? If so, with the right tech it could be down fired to the GO-3 specs. And by "the right tech" I mean it's not just a nozzle change. It's possibly air tube, nozzle assembly with the correct static plate, head, pump pressure, combustion, smoke, and draft tests.

They're virtually the same block with the middle section in the 3 the same size as both middle sections in the 4. The 4 actually holds less water than the 3.

As far as the aquastat, the newer revisions of that boiler come with the Hydrostat 3250 Plus. There are no differential settings because it varies depending on input. It would also give the boiler LWCO protection.

alboguy · January 23

Should I have it repiped the return to 1 1/4 inch and the feed to 1 1/2 inch?

EdTheHeaterMan · January 23

alboguy said:
Should I have it repiped the return to 1 1/4 inch and the feed to 1 1/2 inch?

No You should have a smaller boiler. bigger pipes will not make your house use more heat than it needs.

alboguy said:
Which aquastat should I get?, my water heater is electric.

The ones that will work on your boiler all have small differential on the high limit. You will need a time delay wired into the burner circuit in order to increase the off cycle time of the burner. I don't think that is recommended but if you are handy with electrical controls you could try to place this on your B1 from the L8148 control you have in order to keep the burner from coming back on so soon.
https://www.supplyhouse.com/ICM-Controls-ICM203B-ICM203-Delay-on-Break-Timer-03-10-Minute-Knob-Adjust-Delay?_br_psugg_q=icm203b

alboguy · January 23

Ok thanks for all your help, what about the circ pump, is it worth putting a 0010 in there for better flow?

mattmia2 · January 23

No. If the emitters can only output say 80,000 btu/hr a bigger circulator isn't going to change that.

Venturi monoflow circ pump

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