Monoflow tee

bpkiely · August 2023

I am installing a kickspace heater off a series loop hydronic system. The kickspace is above the piping so I know I only need one monoflow tee. The tee I am using is monoflow tee (scoop tee) and not a venturi tee. Everything I have read that is in this application the monoflow should be on the return side of the kickspace, but the tee manufacturer, Legend Valve, clearly shows it on the supply side when using the monoflow and return when using a venturi tee. My supply house counter guy who has been there for 30 years and is pretty knowledgeable also said to put on the return side. I do not see any reason this would not work correctly on the supply side. Am I missing something?

bpkiely · August 2023

Just to add to my post Beacon Morris shows a scoop T or venturi tee on the return. If I do this the arrow on the tee will be pointing in the opposite of the direction of flow which I can see confusing someone in the future.

EdTheHeaterMan · August 2023

Actually the return is a little better, but you are correct it will work on either side.

Back in the 1950s when Mono-flo® or other venturi tee systems were popular, the diagrams showed that using a single tee on the return would create a "Venturi" effect when placed on the return of the radiator. This would provide greater pressure differential because of the ventury action of the accelerated water flow from the restriction of the thru path which would create a low pressure condition from the branch. This lower pressure would draw more water thru the radiator than if it was installed in the opposite direction on the supply side of the radiator.

It is explained in this text https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf on page 22

Now this explanation is there only for explaining why a zone valve may cause a problem on this type system there is a small clue in the text about this system design. Someone who designed that system years ago needed to select the proper tee fitting in order tpo create the proper pressure drop so there was just enough heated water going into the radiator while leaving the right amount of heated water to continue thru the main in order to heat the rest of the radiators on the main.

Since you are using a tee fitting to divert water from a series loop baseboard system, your probably going to be using a 3/4" thru by 1/2" branch fitting. In the submittal for these fittings there is an indication that you should only ust the 3/4" x 1/2" tee on the return side. https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/submittal/a-420e.pdf

hot_rod · August 2023

if the heater is a high pressure device, as that kickspace heater may be, then 2 diverter tees may be best.
At least a foot of straight pipe between the tees.

That kickspace heater will pull down the temperature to all the downstream emitters, if that matters. It's a series loop, really.

bpkiely · August 2023

Thanks for the replies, I think I will put on the return side.

GabrielRamos · December 2024

Anyone see this type of monoflo fitting? Tees appear to be identical no marking or designation on them, but each supply tee has this fitting. I believe the heating elements were changed from stand up radiators to fin tube baseboard. There appears to be sufficient element, but not getting hot. I believe there is air loop. There are bleeders in baseboard tees on both ends of baseboard run in room with a valve on return right before the pipe returns to basement back at location of original radiator. There's about 20-25' of Piping between valve and vent in baseboard tee on return. I'm leaning towards recommending install purge on return down at main loop. Any experience or suggestions? Pressure is good, circulator is going, first floor heating up.

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