I purchased some Runtal base board heaters a while ago. I am trying to install them into an existing multi zone fin tube system. In the zone I am trying to install them I have fin tube before the Runtal and some fin tube after the Runtal (these are all separate rooms on this zone). I feel like I need some sort of temperature controlled diverter so that I can balance the Runtal with the other fin tube that come after in the flow. Runtal makes the temp control valve but I need one that can either be put in my basement with a remote temp sensor in the room with the Runtal or connected to the Runtal inside the room and I guess I would run another pipe to the diverter bypass. The bypass would go directly to the next room where there is fin tube. Can I do this manually with a mixing valve or what is the right thing to use?

To hopefully better illustrate my system, the zone I am working on has the following water flow path:

boiler -> Dining Room (fin tube where thermostat is) -> Foyer (fin tube) -> Office (where I want new Runtal) -> Bathroom (fin tube) -> return to boiler

I guess the other way to do it is to plumb a new zone to just the office and bypass the office on the zone described but that might be difficult because I would need a new manifold with more zone valves.

Thanks for any info.

Edit, added pic of zone valves: enter image description here

1 Answer 1


Your Runtal baseboard will work best if you supply it with full-temperature hot water that has not been cooled by running through fin tubes.

You don't need a new manifold. You can T-off a new zone with its own zone valve and thermostat for the office by installing a T anywhere in the dining room supply before its zone valve. This design makes several assumptions:

  • The zone valves are on the supply side
  • The thermostats energize the zone valves (only)
  • The "valve open" switches in the zone valves energize the zone controller
  • The office and dining room zone valves are connected in parallel to one zone of the zone controller
  • The pump has adequate capacity for the additional zone
  • The pump is on the return line just before the boiler

If any of the above conditions are untrue, it's not a deal killer, you just have to proceed differently. For example, if each existing zone has its own pump, the wiring and plumbing will be different. Or, say if the zone valves are on the returns in your system, the T will be on the return after the dining room's zone valve.

  • Yeah, my zone valves are all on the return side and I have a single circulator pump as you said, right before the boiler. I misspoke when I said "manifold", it appears that my zone valves all connect with a 1 or 1.5" fittings all side by side, the last being a 3/4 to 1" fitting, all the zones are 3/4" copper. So, if I was going to add a zone it would probably be best to just do it like the others and supply the office by teeing off the "trunk" line, then I guess, like you said, just jump the foyer straight to the bathroom so that loop stays the same.
    – jmichas
    Sep 29, 2022 at 23:10
  • @jmichas Agreed. And since you have only 1 pump, there's probably no multizone controller, just a relay for the pump energized by closure of any one of the zone valve switches. Very simple! The most important takeaway though is that performance of the Runtal baseboard is strongly dependent on water temperature so it deserves its own supply direct from the boiler rather than the cooler water after the dining room. You'll probably find a chart or curve from Runtal showing BTU per foot of baseboard vs water temperature.
    – MTA
    Sep 30, 2022 at 1:55
  • I have my parts on the way, hopefully it all goes smoothly, it will be cold soon. Do recommend trying to desolder the existing 1 1/4" fittings that make up my zone valves or just cut the last one off and add new?
    – jmichas
    Oct 1, 2022 at 2:58
  • @jmichas Can't see what you have so it's hard to say. Cut and replace is quicker and more trouble-free. Be sure to set zone valves open before heating. Best way I know to get solder off a fitting or pipe for re-use in a new configuration is to make a wad of 4/0 steel wool the size of a matchbook, hold it with needle-nose pliers, smear it with flux and use it to wipe melted solder off the heated joint. It absorbs solder like a sponge and leaves a bright, smooth tinned copper surface. Keep flame away from steel wool unless you like pyrotechnics.
    – MTA
    Oct 1, 2022 at 11:51
  • added a pic of my zone valves if you are interested. Thanks so much for all the great advice!
    – jmichas
    Oct 2, 2022 at 12:24

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