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Heat loss to cinderblock?

Post in 'The Green Room' started by Black Jaque Janaviac, Feb 2, 2012.

  1. Black Jaque Janaviac

    Black Jaque Janaviac Feeling the Heat

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    I've got a stove in the basement. It seems like I've received a lot of advice that the cinder block would soak up heat like I wouldn't believe, and maybe that's so.

    The fact that the stove my stove room is blazing hot while the rest of the house could use a five degree lift leads me to suspect that my problem is moving the heat about, not loss to the concrete foundation. Am I correct?

    I'm trying to figure out where to aim my efforts first - installing floor grates? or insulating foundation walls?

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  2. realstihl

    realstihl Feeling the Heat

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    The hotter the walls get the more heat loss you get. My vote is on insulation first.
  3. Hardrockmaple

    Hardrockmaple Feeling the Heat

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    Insulate. I tried for years to heat my main level with a woodstove burning in an uninsulated basement. Could never get it to happen. A few years back I insulated the basement walls, now I can heat the main level with just the basement stove throughout the fall shoulder season.

    Insulate.
  4. PLAYS WITH FIRE

    PLAYS WITH FIRE Minister of Fire

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    I say insulate which will cost some coin! But the time and effort you save from keeping more heat in will be saved by using less wood. Then spend 20 bux and buy a box fan, point it down stairs into the stove room until you save enough money to do some clever ducting like I have planned tis summer!
  5. nate379

    nate379 Guest

    Cinder block without no insulation is something around an R2. I'd insulate at least the section that is above the dirt level.
  6. daveswoodhauler

    daveswoodhauler Minister of Fire

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    Put 1" rigid insulation on my basement walls for the kids playroom. With the IR gun, the temps are about 10 degrees warmer with the R5 vs just the concrete foundation walls. Basically, if I take a reading on the interior wall above grade in the basement, the non insulated wall will read 48-49 degrees vs the insulated wall at 58-60 degrees at the same height. I don't have heat down in the basement yet, but think it would be a good idea for you to at first insulate, then look at something to move the air (grates, fans etc...)
    The 2 X 8 X 1" sheets I got were like $8 a piece and easy to install/cut as they were tounge in groove
  7. Black Jaque Janaviac

    Black Jaque Janaviac Feeling the Heat

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    I would imagine this is done by insulating on the outside. This could be tricky as much of the perimeter is surrounded by garage and/or raised cement patio or porch. I suppose it just wouldn't get done along these sections.

    Can you recommend type of insulation?

    How to install it (painted block)?

    How to cover it? (it sounds like I could put up foam, fasten metal lath somehow, then shmear drywall mud over all)
  8. realstihl

    realstihl Feeling the Heat

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    It'll still soak the heat like a sponge. Best way is to frame walls out then insulate. Firring strips will work also.
  9. Black Jaque Janaviac

    Black Jaque Janaviac Feeling the Heat

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    What's the difference between framing out and firring strips?
  10. Black Jaque Janaviac

    Black Jaque Janaviac Feeling the Heat

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    Oh yeah. Instead of floor jacks my basement has interior cinder block walls. I can't imagine those would need to be insulated but I figure I'd best check first.
  11. Hardrockmaple

    Hardrockmaple Feeling the Heat

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    Inside of exterior walls. You'll find a huge difference.
  12. Locust Post

    Locust Post Minister of Fire

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    Firring strips aren't as thick as framing with 2x4s. Depends on how thick of insulation you want and if you intend on drywalling later.
  13. Battenkiller

    Battenkiller Minister of Fire

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    I agree. It's not that the blocks themselves act as heat robbers, it's the fact that they have basically no insulating value and heat is lost to the above-grade portions of the basement perimeter.

    Heat flow increases as the temperature differential increases. The ground below the basement floor in my area is around 55° year round, but the outside air surrounding the above-grade portion of the foundation may get down to 25 below. That's more than a 100° temperature differential if you're running that stove like most basement burners do. Heat is just pouring through those blocks in those conditions.

    To make matters worse, the parts of the foundation exposed to the outside air have no heat storage capacity. While the below-grade portions of the basement store more and more heat as the heating season progresses, the heat that passes through the upper portion conducts through the foundation walls and is instantly whisked away by the outside air.

    Short version: get the upper 4' of the basement walls insulated to at least R-15 and you will see a big reduction in heat loss.
  14. smmm

    smmm Member

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  15. Ehouse

    Ehouse Minister of Fire

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    Here's an easy fix that worked for me. Depending on how and where your stove is situated, build a three sided plenum (box) with the open side facing the stairwell. Allow plenty of clearance from the stove on all sides and line it with a reflective material ( I used some old 4' square highway signs at first). A large percentage of the heat lost to the block is from radiation. If your stove is close to a corner, you only need to put up one side of the box. Reflectix (that bubble wrap stuff) works great as it provides the required 1/2" to block radiation, but remember it is flammable so give it clearance and fasten it securely to the inside of the plenum walls.

    Ehouse
  16. PLAYS WITH FIRE

    PLAYS WITH FIRE Minister of Fire

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    A useful heat loss calculation I use frequently is:

    Btu=U*A*(T1-T2) where "U" is the reciprocal of the "R" value and "A" is the area of the wall. T1 and T2 are the change in temp from inside to outside.

    This will give you heat loass per hour from the wall. The nice thing is you can see what will happen when you add the insulation just how much you have saved. I know there are calculators for this but this is the simple equation and I like to sometimes do it the hardway!
  17. Wood Duck

    Wood Duck Minister of Fire

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    one nice thing about the method shown in this link is that the first step - glueing foam insulation to the cinder black wall - is pretty easy and quick, and you'll make a big difference in the heat loss just by doing that first step.
  18. peakbagger

    peakbagger Minister of Fire

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    One advantage of a conrete block wall is that you dont need to shovel snow around the house as it melts rapidly. My mother used to grow roses up in Maine (which was a challenge due to cold weather). Her graden was up against the house and the heat from the woodstove kept the roses warm int he winter and they bloomed right up int he spring .

    Whatever you do dont get convinced to drill and foam the interior of the blocks, its a waste of money that would be far better spent on proper insulation.

    One caveat is that if you are in wet area with clay soils, there is remote chance that if you do too good of a job at insulating the foundation that you could have some issues with the clay freezing and pushing in the blocks. This usually occurs when the foundation wasnt backfilled properly with gravel and lacks drainage. Year ago I had a house in Wisconsin that had been repaired from a similiar situation. It wasnt just my place, the entire neighborhood had the same issues and repair.
  19. Butcher

    Butcher Minister of Fire

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    I've found just the oppisite effect in our home. It may have to do with the stove being in the center of the basement close to the stairs or the heat ducts being almost right above the stove or it may be in the way our house is constructed. I've found that as the basement cools alott of times the temp upstairs will actually rise.

    [​IMG]
  20. Black Jaque Janaviac

    Black Jaque Janaviac Feeling the Heat

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    Interesting I calculated the heat loss for the top two block that are exposed to the atmosphere and for the lower 5'8" which would be covered w/ soil. Assuming R-5 and the outside temp was 10* and the room temp 80* the top two blocks were losing 440 BTUs/hr. The portion below ground was losing 680 BTUs per hour using the same R value but increasing the area of course and reducing the gradient by assuming outside temp of 55*.

    So the top 24% of the basement wall was losing 65% of the heat! So to maximize the heat savings per dollar spent it would seem to make the most sense to insulate on the outside by just digging down a bit and slapping up foam board insulation and parging over that. I realize the weakness would be the assumption that all 5'8" of buried wall is exposed to 55* soil temps. Frost does penetrate.

    Interestingly there is not much of my basement wall that is actually exposed to the outside air. Probably 1/2 to 2/3's of the perimeter is covered by either heated breezeway or concrete porch/patio. So to insulate the outside actually would not involve too much work.
  21. PLAYS WITH FIRE

    PLAYS WITH FIRE Minister of Fire

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    If I understand corectly what you did you are losing more heat from the area below grade? That should be the opposite as the area below grade should have less of a temp change and the btu loss is less. I would say anything exposed to direct elements is going to lose more and anything below grade (ignoring frost line) should lose less.

    If 100 sqft BELOW GRADE and r=4, inside temp =80, 50 being below grade temp:

    1/5=.2

    .2*100*(80-50)=600btu/hr

    then:

    100 sqft ABOVE GRADE and r=4, inside temp =80, 10 being above grade temp:

    .2*100*(80-10)=1400btu/hr

    Unless we are saying the same thing and I can't read real well.......
  22. Seasoned Oak

    Seasoned Oak Minister of Fire

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    I recently read that an uninsulated block wall Basement can lose as much as 1 million Btus per day.
    That would be ALL the heat from a stove putting out 50000 Btus per hour for 20 hours.
  23. PLAYS WITH FIRE

    PLAYS WITH FIRE Minister of Fire

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    Ahhhhh, I read more better you increased the area below! Sorry!
  24. peakbagger

    peakbagger Minister of Fire

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    I usually assume cinder block is a lot lower than R -5.
  25. ozzy73

    ozzy73 Member

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    Insulation is the key here. We went from bare block walls to R24 insulation on the walls ( 2" Rigid insulation R10 + R14 bats ) and R28 in the headers.
    I could not believe the difference the first winter.

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