Help adding extra baseboard

Fus1982

Hello,

I added 22' of slantfin baseboard to an added room. There were 4 existing cast iron baseboards on the zone that i tapped into. This is a single loop system with monoflo's on the supply side and regular Tee's on the return side. I extended the 1" main loop to follow the path of the new baseboards that I just added.
After turning the heat on for about 30 minutes, all of the old baseboards heated up to about 120 degrees, but the new baseboard only reached about 85, and that was only at the supply side. The return side was around 75 as it barely got warm. Where did I go wrong with this and what do i need to do to fix it? A few notes that I can think of.

1 - All of the existing monoflos were 1"to1"to1/2", so I used the same for the new one. Should I have used a 3/4"? I'm thinking that possibly I'm not getting enough flow on the 1/2" feed?

2 - I put the bleeder on the supply side where the monoflo comes in, would moving it to the return side fix this problem? Note: I checked all existing in the house, and it seems like most of the slantfin baseboards have bleeders on the supply end and the cast irons (all but 1) have the bleeders on the return ends. I've read that this was incorrect, but it has been working for the last 65 years (assuming it's all original to the house)

3 - I attached a quick diagram to show the set up, the red is the existing and the blue is the new

I'd appreciate any input, thanks!

mattmia2

You need to make a separate zone for the fin tube. It heats very differently than the ci baseboard and adding all that resistance to one branch of the monoflow will change the balance of the whole system.

Fus1982

Thank you.. I didn't think it would be an issue since 2 out of the 4 heating zones in the house have a mix of CI & fin tube and it's always worked fine

EBEBRATT-Ed

How many total feet of baseboard do you have? Where on your sketch are the Monoflo and regular tees at? Are you feeding the whole loop in that room off the two tees from the main or do you have separate tees for each of the 5 sections of baseboard? If the rest of the house heats and this room haeats porley you may have air trapped somewhere.

Fus1982

The monoflo is where the tip of the red arrows are (supply side), and the other end would be the regular tee. There is a separate monoflo tee for each section, so 5 monoflows altogether. There was about 40' of existing cast iron baseboard, now an additional 22' of fin.

EBEBRATT-Ed

@mattmia2 is right it is best not to mix fin tube and cast iron. But your in an existing room just trying to boost the heat. I think you are air bound. Run the heat check the pipes in an out of all baseboard.

Hot in cold out =no flow or air bound.

Monoflow is notoriously difficult to bleed.