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hot water heating: series vs. parallel

unsureunsure Member Posts: 2

We just moved into a house with hot-water baseboard heating. When we woke up yesterday to no heat, we called a plumber (we have a home warranty) who fixed the problem by bleeding all our radiators.

Now that he's showed us what to do, we can bleed the radiators ourselves from now on. However, he also told us that our pipes (originals, from a house built in the 50's) were plumbed incorrectly: the radiators are in parallel,  but they should be in series. He says that will make it easier to maintain the radiators, since that way there will be just one bleed valve in the basement.

The cost of the job will be a couple thousand $$$.  Is this reasonable advice? The heating system house has three zones: Zone 1 for the main house (single story) about 1600 sq. ft., Zone 2 for the basement, and zone 3 for an 800 sq. ft. addition. The pipes he recommended we replace are in zone 1, and can all be accessed through the (unfinished) basement ceiling.

Thanks for any help you can provide!



  • Paul PolletsPaul Pollets Member Posts: 3,017
    Pumping Away piping strategies

    Parallel piping (each radiator has its own supply and return connected to the radiator mains) is the preferred method, as all radiators will get warm at the same time.  Series piping (the radiator's return becomes the next radiator's supply) has its pitfalls, as the radiators tend to heat unevenly.

    The most common problem in older systems is the pump location on the boiler. It should be on the supply header pumping away from the expansion tank. Dan H. has an excellent book called "Pumping Away" that explains the method, in great detail and in layman's terms.  If you read it, you may find you know more than most heating techs.
  • unsureunsure Member Posts: 2

    Thanks, Paul. Your advice makes sense -- seems like converting to series will mean that the first radiator gets the hottest, followed by the next, and the last few radiators on the loop may not heat up much at all. So, I'm tempted to save the money and leave the system as is -- the pipes are old but they're not leaking.

    I may try to get ahold of the book as well. The pump on our system (or, what I think is the pump -- a red device labeled "circulator") is on the main return line, after the return lines from the three zones have merged together, right before the water goes back into the boiler and expansion tank. If I understand your post correctly, that means the pump is mounted in the wrong place -- it should be on the main outgoing line, pumping away from the boiler & expansion tank. Will moving this pump make the heating system more efficient?

  • Paul PolletsPaul Pollets Member Posts: 3,017
    Pumping Away

    Moving the pump will make a huge difference.  Make sure to install a good air eliminator (Spirovent) on the supply header and use a pre-charged expansion tank to replace a steel tank, if you haven't already.
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