I am in the process of adding a new baseboard heater and I am trying to figure out the proper way to drain my system. I believe I will first need to shut off the valve on the right in the picture below, which should be feeding the zone that I am targeting.

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Secondly, I believe that I will need to shut off the return valve for the zone. In the picture below, the three valves on the right all seem to be return lines for that zone. So my first question is, do I need to shut off all three of those return valves? And my next question is where should I hook up the drain hose to? All three of the return lines has a spigot. Can I drain for any of those three, or should there be a main drain line somewhere else? I've added another photo below showing the entire system setup.

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  • You'll need to let air in somewhere...do you have bleeders you can open?
    – Ecnerwal
    Commented Oct 13, 2023 at 15:20
  • yes, there are bleeders on most of the baseboards. how many bleeders should be opened? Commented Oct 13, 2023 at 15:23
  • 1
    One might be enough, but with it dividing into 3 parts you might need one on each part to get effective drainage - without a complete layout of the system piping it's hard to be certain. The highest one would normally be sufficient, if you can identify it, as air should move through the pipes to allow it to vent the others, but sometimes heating loops end up with sections that act like traps, from wiggling around the building, and opening more might be needed.
    – Ecnerwal
    Commented Oct 13, 2023 at 15:37

1 Answer 1


If you don't know which of the 3 returns on the zone affects the specific area you are working, you will probably need to use all 3.

You might do better with a bucket than a hose if you don't have bleeders on the top sections of the loops you can open to let air in - using a bucket you should get air "glugging" back into the pipe from the valve, with a hose it too easily gets stuck in the hose and air can't get back in - but you say you have bleeders, so you can just open them to let air in so water can more easily drain out.

The pipe from the shutoff above the zone valve won't drain in either case, up to the point that the piping turns horizontal so it can drain out the side with the drain valves.

Expect to find some residual water when you cut into the pipe - have shop towels and/or a wet vac handy when you do. Don't use the nice bath towels, they will get stained and it won't come out.

  • excellent info. thanks so much. Commented Oct 13, 2023 at 15:39

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