Did venturi tees on baseboards work well? – GreenBuildingAdvisor

A friend has a single-story house in climate zone 7 with an older, non-condensing natural gas boiler. The home is heated with hydronic baseboards on a single zone. There is a single 1-inch main loop running around the crawlspace that serves roughly eight baseboard units.

Each baseboard branches off the main using venturi (diverter) tees—mostly 1″ × 1″ × 1/2″, with a few that may be 1″ × 1″ × 3/4″. 

The issue is the hours it takes to bring the house up to temp on a negative or single digit Fahrenheit  day if it is set back during the workday.

I have not yet measured the temperature difference on the supply/return. However, I do believe the boiler to be adequately sized to keep up with the load.

Did these diverter tees end up working well? I have never seen them before.

Considering axing the diverter tees and running a Pex loop around the crawlspace with  each baseboard plumbed in series.

Any insight would be greatly appreciated 

Edit: I have opened the coin valve on each baseboard to ensure there is no air trapped. The zone valve is brand new.