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Radiant Floor Heat Not Warming House

luddite20 | Posted in Energy, Heating & Insulation on January 24, 2012 08:34am

Ok, I’d love some advice here.    I recently installed a hydronic heating system in my 800 sq. ft.  home here in Berkeley, CA.  I have a 1941, run-down, fixer upper with hardwood floors throughout most of the house.   I ran about 1000′ of Pex tubing between the floor joists and stapled it up with aluminum transfer plates.  I built a manifold that runs off of a tankless water heater that ties both the domestic hot water supply and radiant floor together (open loop—hot water that comes out of shower first goes through floor—this system is very similar to one created and sold by Radiant Company in Vermont.)  In terms of insulation, I stapled up an ecofoil radiant barrier about an inch below the pex, and R-19 fiberglass below that in every area except my bathroom, which is currently leaking from the shower drain and therefore left uninsulated until I can attack that project.  The home has been seismically retrofit, and there is no insulation behind the sheerwall.  I tried to leave a tail on the end of the insulation to bring over the rim joist, but it’s not that tight, and the crawlspace itself is vented.

And…..the attic has Zero insulation at this point (as of today I am in the process of updating the knob and tube that runs through the attic in order to insulate.)

Now, I have the system under 1 zone with 4 seperate loops of about 250′ each.  Now here’s the problem.  My house doesn’t seem to be able to get above 67 degrees, and that’s if I let it run for 24 hours.   If I do let it run for 24 hrs, I’m using around 4 therms, which, in my humble opinion, is far too much for 800 sq. ft.  

Is anyone willing to lend an ear?  I have invested a lot of hard time into this here project, and currently feel as though I’ve failed.  Ex post facto, I don’t believe radiant floor heating is ideal in this climate, but at this point this is neither here nor there.  I was really excited to install this and here I am. 

 

Help?!!!

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Replies

  1. luddite20 | Jan 24, 2012 08:36pm | #1

    and most importantly, my wife is cheap and cold.

  2. luddite20 | Jan 24, 2012 08:48pm | #2

    additional info

    Also, the supply temp is 125F.  I had it set at 135F but then I noticed the floor boards I recently refinished were cupping/seperating!!!  Return temp is 114-117.  So temp drop is around 20 degrees.

    The 4 loops run off of a 3/4 pex header.

  3. DanH | Jan 24, 2012 08:53pm | #3

    Well, first, no need for the double post.  Every post gets read by just about everyone.

  4. DanH | Jan 24, 2012 09:01pm | #4
    1. How was the house heated previously?

    2. How do you balance the loops?

    3. Describe your loops and pump arrangement a little better.

    4. Oil, propane, or natural gas?

  5. KDESIGN | Jan 24, 2012 09:55pm | #5

    Inadequate Insulation

    If you are using too much energy and not getting enough heat for the house, it sounds like the insulation is inadequate.  If instead, the problem were with the heat distribution system being unable to deliver sufficient heat, then you would not see excessive fuel usage. 

  6. KDESIGN | Jan 24, 2012 10:23pm | #6

    All the insulation has to work together, so it is hard to comment without seeing exactly how it is all set up.  What type of insulation is in the walls?  What thickness is it?

    1. luddite20 | Jan 24, 2012 10:29pm | #7

      ah, now we get to this.  There is nothing in the walls, as is all too common in Berkeley.  I've thought about cutting in the the walls and blowing down, but there is the attic to contend with first.  

      1. DanH | Jan 24, 2012 10:37pm | #8

        First thing to do is to seal the air leaks.  Likely there are spots where you can see daylight.

      2. NRTRob | Jan 25, 2012 10:39am | #11

        the only thing to talk about here

        is how to insulate.  4 therms at  80% efficiency and 800 square feet is only a sustained heat load of 16 BTUs/sq ft.  If anything, I'd say that was low for an uninsulated building, even in your climate.  Congrats, you're getting off lucky.

        insulating will of course reduce this significantly.

        1. User avater
          xxPaulCPxx | Jan 25, 2012 12:37pm | #12

          Exactly

          Radiant heat isn't like forced air, where you feel a direct effect... it's alot more gentle, and better suited to a house where a good sealing and insulation system works in conjunction to create an even heating effect.

          Do the air sealing and insulation, then you get to come back and complain if you don't think your heater is working up to snuff!

  7. DanH | Jan 25, 2012 07:14am | #9

    What temp do you manage to achieve on the outgoing heating loop -- seems to me you'd be dragging a fair amount of cold water through the loop with that piping scheme.

  8. DanH | Jan 25, 2012 07:16am | #10

    Use the temp gun from above, pointed at the floor and baseboards and lower walls, looking for air infiltrating from below.  Also check electrical outlets.

  9. NRTRob | Jan 25, 2012 12:56pm | #13

    that will probably knock a quarter off.

    doing the walls would probably knock off another quarter or so.  Just round guessing but should be a ballpark.  of course the usage per day varies based on how cold it is outside.

  10. srb2020 | Jan 25, 2012 10:35pm | #14

    You need to do a heat loss calculation with all of the proposed future insulation you plan to install.  That should give you a really good idea if it is ever going to work.  800sqr ft is not a lot of radiant surface to overcome the kind of heat loss you describe.  There are some great on line companies that can do that for you but they need complete plans and specs (they'll tell you exactly what they need).    My 800 sqr ft bungalow in climate zone 6 did not have enough surface area (in the floor) to consider radiant floor heat.  The high number of windows was also a factor.  In your climate zone it might be ok once you've insulated but you really need to do a heat loss calculation.

    Good luck.

  11. sapwood | Jan 26, 2012 10:43am | #15

    Personally, I think its nuts to do anything at this point other than insulate. A ways back in this discussion you asked if spray foaming a rim joist would do any good. That's simply goofy without first addressing the walls and ceiling. You've got the radiant system installed so there's no point in now doing the design for it. I wouldn't be distracted from the primary goal. Reduce heat losses first. Spend your money where it will do the most good.

    1. cussnu2 | Jan 26, 2012 02:00pm | #16

      It may be goofy and then again it may not be goofy.  I saw on here or Green Building Advisor a case with radiant flooring that wasn't performing up to standard and in that case they found that the loops were in contact with uninsulated rim joist in each bay.

      1. calvin | Jan 26, 2012 02:31pm | #17

        I'm hoping he knew.........

        That it's wise to run to the most heat loss areas first-outside walls etc, then work your way back to the return.

        DIY is fine and I commend anyone for trying (like most, I've DIY'd many things I'm not adept at), but-design and spec'ing a heating system is not fly by the seat of your pants.  Once he stuffs the heat loss points and insulates, I hope his dreams of wonderful radiant heat, are realized.

        1. luddite20 | Jan 26, 2012 02:59pm | #18

          calvin-

          I"m a persistant

          calvin-

          I"m a persistant bastard, so I will keep at it.  I am going to first finish re-wiring attic for that to be insulated.  Then walls when I get a chance.  As for the rim joists, my loop ends were help back 18" from them to minimize heat loss through that area.  I really appreciate you help.

          1. calvin | Jan 26, 2012 03:16pm | #19

            lud

            Persistance in the face of defeat wouldn't be smart.  But then again, this isn't the bighorn.  I'm sure you'll get this working to your satisfaction.

            One question tho-here with the slab-we ran tighter spacing around the perimeter for that reason-heat loss.  Rather than avoid it because of heat loss-we increased the amount of hose to make up for it.   Now, I've got and inch and a half foam between the block foundation and the slab-I still find cool concrete beyond the hose-not bad, but a noticable difference in toe temp.  I wonder if you shouldn't have pushed that hose closer to the band.   Did you run tighter hose spacing where you could (parallel joist/foundation/band)?

            I'm thinking that the comparison between running in slab and between joists is not really applicable.  But it's just a thought.

            Rob is pretty sharp with this stuff, hope he's here to offer further info.

            Best of luck!

            and please, report back-those of us that read this stuff hate to miss the next chapter.

            thanks.

            EDIT:   Well let's see-sexism in the word filter?

            Persistant bastard?          Persistant bitch?

            What's wrong with that picture?

          2. luddite20 | Jan 26, 2012 03:22pm | #20

            Persistance in the face of defeat?  Jeez, that reminds me of my wife.  Before I throw in the towel I have to insulate at least the attic, which has nothing at this point.  As for the loops, they are built off of parallel headers.  I used 1/2 pex and 1 loop per bay (2 1/2" lines per bay).  I used 1/2 because of workability in such a tight crawlspace.  I didn't want to put the loop ends any closer than 18 inches from rim joist even if I do really go at it with more insulation, as I was worried that even with that insulation, the fact that the shear walling is covering up non insulated areas about the sill place would render the rim joist insulation moot.  I will keep you all updated, whether it's a success or walking to the gallows.

          3. luddite20 | Jan 26, 2012 03:24pm | #21

            when you mention "rob", do

            when you mention "rob", do you mean NRTrob?

            chad

          4. calvin | Jan 26, 2012 03:29pm | #22

            Chad

            yessir, NRTrob.

            And what the heck-I thought you were living in California?   You need heat in California?

            Why the hell would you ever settle down in California?

            if you need heat.

            But I digress.

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