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Thread: Adding baseboard heating to my current system.

  1. #1
    DIY Junior Member akr44's Avatar
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    Default Adding baseboard heating to my current system.

    I have in-floor pex in my house, but when I built the house, I stupidly didn't compensate for having about 1/3 of the house open to the upstairs, which means less floor with pex in it. So, my house doesn't get warm enough and I'm wanting to add baseboard heaters in the living room where there isn't sufficient pex. So, I need to tap into one of the zones I already have set up, but my living room zone already has 5 rolls (150 ft each? or whatever the standard is) of pex on it. My brother-in-law told me that I shouldn't put more than 5 rolls of pex on a zone, but is this true? What is the logic to this if so? My alternative is to create another zone with it's own thermostat, so I'd have two thermostats in the living room, or to add it onto another zone with less pex, but then it's dependent on the wrong thermostat. I'm not sure why it matters how much water you have running through one zone. Does it mean that it's taking the water longer to cycle through the boiler? I've noticed that one room in our house has only one roll of pex and it stays warm fairly easily. Thanks for any advice.

    Edit: I could also add on some electric baseboard heaters, which would be much easier. I'm not sure how much less efficient they are than my gas boiler system.
    Last edited by akr44; 11-12-2012 at 05:26 AM.

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    In the Trades Tom Sawyer's Avatar
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    If its 1/2" pex the longest runs shouldn't be more than about 130' max.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    In the trades Dana's Avatar
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    Assuming your have 5-port manifolds splitting the zone in to 5 loops rather than one long skinny 750' snake you should be able to get reasonable performance out of it, but you have to do the math on how much pump you need, and unless the run between the boiler & manifolds is very short you'd want at least 3/4" to the manifolds. There are many decent radiant designs running with 200', even 300' loops, but they're designed, not hacked, with the right amount & type of pump behind it.

    If you spliced it all into one long you'll have to break it up- that's a lot of pumping head and you won't get adequate flow even with a fairly monsterous pump.

    If it's natural gas rather than propane I'd expect the electric heating to cost 2.5-4x as much as gas-fired baseboards- depends on your actual gas & electric rates.

    Rather than fin-tube baseboards which don't emit a lot of heat at radiant-floor temps, european style low temp panel radiator/convectors can put a lot of heat into a room without a lot of plumbing. Putting a loop with a few of these on it in parallel with the radiant floor (and a ball valve to throttle back the flow to the panel radiator branch so's you can feel at least some heat in the floor) would be more comfortable fix than any fin-tube baseboard solution.


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    DIY Junior Member akr44's Avatar
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    Quote Originally Posted by Dana View Post
    Assuming your have 5-port manifolds splitting the zone in to 5 loops rather than one long skinny 750' snake you should be able to get reasonable performance out of it, but you have to do the math on how much pump you need, and unless the run between the boiler & manifolds is very short you'd want at least 3/4" to the manifolds. There are many decent radiant designs running with 200', even 300' loops, but they're designed, not hacked, with the right amount & type of pump behind it.

    If you spliced it all into one long you'll have to break it up- that's a lot of pumping head and you won't get adequate flow even with a fairly monsterous pump.

    If it's natural gas rather than propane I'd expect the electric heating to cost 2.5-4x as much as gas-fired baseboards- depends on your actual gas & electric rates.

    Rather than fin-tube baseboards which don't emit a lot of heat at radiant-floor temps, european style low temp panel radiator/convectors can put a lot of heat into a room without a lot of plumbing. Putting a loop with a few of these on it in parallel with the radiant floor (and a ball valve to throttle back the flow to the panel radiator branch so's you can feel at least some heat in the floor) would be more comfortable fix than any fin-tube baseboard solution.
    Alright, thanks, I'll see if I can find those around here.

  5. #5
    In the trades Dana's Avatar
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    Like anything else if you can't find them locally you can order via internet and pay exorbitant shipping to more remote AK locations, but I'd think if you're near Anchorage there's hope that somebody stocks them.

    Most will put out about half their 180F nominal rating with 130F water, which is useful for figuring out how much it puts out at radiant floor temps. (You can interpolate linearly from the 180F and 140F specs.) If the zone is keeping up mostly you can probably go with something rated 10,000-13,000BTU/hr @ 180F.

    It's a lot more expensive than fin-tube, but unlike fin-tube it's still putting out a reliable-knowable amount of heat even with sub-100F water. Taller is generally better for keeping output linear with temp at very low temps. (A 24" tall panel radiator has a more reliable output with 85F water than a 12", but even a 12" tall version blows away any fin-tube at low temp.)

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    DIY in AZ emd36's Avatar
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    All the documentation I have read says that 1/2 inch pex running with a correctly sized pump for the pressure loss over the distance can be up to 300' in length. (330 actually, but limited to 300 on the conservative side.) Why would you limit the length to 130'?
    Sounds like this install did not have accurate heat loss calculations, or the design temp was too high for the AK conditions.
    I'm designing for 0 degrees in the Colorado front range--Zone 5. Indoor temp at 70 degrees. I will have one radiator loop from the older part of the house that is not being remodeled. Each of the zones are on their own thermostat and control although one zone has two loops of pipe. I will run the boiler hot enough for the radiators (need a higher water temp) and use a temperature mixing valve to run the radiant at the design temp which is 120 degrees for an 84 degree floor which should maintain 70 degrees interior at zero degrees outside. Of course if it is colder, will have to run the pump more often or supplement with a wood stove. I have a Wirsbo manual that is an older edition but has all the basics of the design, including the info about using radiators and radiant on the same system. Downloaded a Manual J program that created the heat loss calculations based on the insulation and other factors. It took some time to learn enough to design a system but I feel more confident with this design than the HVAC vendor who just wanted to install by "rule of thumb". There seem to be several things you could do before you decide on the radiators: 1) Figure your home's heat loss, especially in that cold room, 2) Consider putting in more thermostats, maybe one on each zone? 3) Consider a higher volume pump 4)Consider an outdoor reset mixing valve and running your boiler at a little higher temp. These would probably all be less expensive than more radiators.

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