I have an old house (~130 years) that has a hydronic baseboard system installed. The heating system is improperly plumbed: the 1st floor thermostat controls half the heating on the first floor and half the heating on the second. The second floor thermostat controls the other half of both floors.

I'd like to fix it.

The current system seems to use diverter-tees. More importantly, not all of the piping running to the baseboards are the same size. I didn't measure exactly, but I think most of it is 3/4", and some is 1/2".

Can I simply cut out the existing system and connect all the baseboards together in series? Will the different pipe sizes cause significant issue?

My rough plan is to split the floors into two loops each, so that I don't end up with cold water at one end up of the loop.

1 Answer 1


The system you describe is a "monoflo" system. They work pretty well when installed correctly. It sounds as though yours is installed correctly. If you want individual control in each piece of radiation you could add rad valves to each radiator piece. If you are not well versed in this, I would seek professional help so you don't change something that is very costly to fix. Add to your original question so that we all have an idea just what you are trying to accomplish. There are any number of changes and improvements you can do. None are easy or cheap or quick. Please indicate what you are trying to do.

  • I am trying to solve what I desribed in my first paragraph. The system right now is all sorts of wonky. The first floor thermostat never turns on because the second floor thermostat turns on the radiator on the first floor right next to the first floor thermostat. Meanwhile the second floor thermostat never reaches temperature because half of the second floor never turns on. Commented Jul 12, 2017 at 16:15
  • Trouble shooting your system from 30 miles north of Pittsburgh, Pa. is impossible. I would try to find a good HVAC company to look at and assess the system. It sounds as if someone installed this system with very little knowledge on the proper way to install a "monoflo" system. On a true "monoflow system the zoning is done at each radiator or group of radiators or you zone each floor separately. Good luck
    – d.george
    Commented Jul 12, 2017 at 19:08
  • Running all the rads on a single series loop per floor may not be a good idea. I would not do it on any system I would install.
    – d.george
    Commented Jul 12, 2017 at 19:11
  • Yeah, the house actually has 5 zones, but floors 1 and 2 got mixed up somehow. I am simply hoping to untangle them. My rough plan right now is to split into two loops for the first floor (the second floor is smaller). It sounds like maybe I should leave the monoflo system in place, but fix up the main loop itself so that the floors aren't interconnected. Commented Jul 12, 2017 at 20:22

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