heating a garage loft

Discussion in 'HVAC Heating & Cooling' started by Master Brian, Nov 17, 2009.

  1. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    We are looking at heating approximately a 400sqft loft above a garage. Only option is electric as there is no gas.

    Wall insulation is most likely sparse, but this is a double bricked structure with plaster walls, if that makes any difference, but it also has 7 windows and is a free standing structure, so it is exposed on all sides to weather.

    Initially we looked into baseboard heat, which may still be the best option; however, I've been reading about things like the EdenPure heater and am curious if those are a viable option. Reviews seem to be mixed.

    Let me start by saying, I realize they aren't going to provide some "miracle" heat like some people might think. If they aren't a total scam, here is my logic...
    1) I can get an EdenPure that is rated to heat 1000sqft for about $400. Overkill maybe, but I'd rather have too much heater for only $100more, than not enough heater. For $300 they sell their heater that will heat up to 300sqft. These plug directly into a
    2) I'm told the hydronic, liquid filled electric, baseboard heaters are a better bet/more cost effective than just an electric baseboard because they radiate the heat out long after the unit shuts off. Two hydronic baseboards will run about $400-$500, not including cost to install or thermostats. I figure, it'd take 2 units to heat this space. Might try with 1 for starters, but a 2nd would most likely be needed or something else to suppliment with.

    So with that said, I'd love some feedback.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,995
    Location:
    New England
    My sister had a house that was heated with electric radiant panels in the ceiling. they loved it, and the cost wasn't horrible. The panels were white, but may not suit your style. Note, these made the person feel warm, and while they did heat the air and structure some, not as much, so placement is critical. WIth a room over an unheated garage, the floor could end up being really cold. I think to make this comfortable, may take some additional thought. radiant floor heating, depending on planned covering might be an option. you didn't mention where this is located, the weather extremes, or the type of windows. Single pane, and your heat load will be huge. You need to do an analysis on what amount of heat is needed, then decide the most efficient way to install it. Is there going to be water available, would a small boiler be an alternative? Could you get gas there?
  3. Dana

    Dana In the trades

    Messages:
    2,837
    Location:
    01609
    It kinda depends on how much work & $ you're willing to put into it, but a low-voltage radiant floor (Z-mesh, or similar) will be the cushiest at a given air temp, followed by a radiant ceiling, then panel radiators, then oil-filled baseboards. With any radiator system you get some direct radiated heat transfer from the radiator to the occupant.

    Standard baseboards are convectors, and are designed to warm the AIR to make the occupant comfy, which happens at a higher air temp than with a radiator warming up the people via infra-red radiation (the heat-lamp effect.) Since it's the people, not the building that you're most likely trying to satisfy radiant is your best option.

    You can buy quite a bit of insulation for a year's worth of electric heating in a space like this. If the floor & ceilings aren't already well insulated, it's worth retrofitting a bunch (especially if you go with a radiant floor or ceiling.)

    Air tightness also counts- are there any cracks in the mortar leaking air? Are the windows all tight (and double-paned/stormed). Is this a cavity wall, with an air space between the wythes of brick? If yes, in some climates you can safely blow EPS bead insulation into the cavity and get another R3 or so (more if the cavity is more than a couple of inches wide), which is a LOT for what's likely to be at best an R2-2.5 wall structure.

    If you're up for redoing the interior walls you can get a lot out of 2" thick rigid iso-board (~R13-ish) pr XPS (R10 pink or blue), either of which will outperform a 2x4" studwall with R13 batts. Hold it in place with furring through-screwed into the masonry, hang the blueboard/sheet rock on the furring. Caulk, foam seal, or FSK-tape the joints as a vapor retarder to keep he masonry from absorbing condensation. It eats up less space and thermally outperforms a batt-insulated studwall. (If you're cheaping out, go with 2.5" thick foil or poly-faced EPS bead-board, which is also about R10.) If you use foil faced insulation with the shiny side facing the room the trapped airspace made by the furring & gypsum buys you another R4 or so.

    ...all of which is a lot more than the "EdenPure or baseboards" question...
  4. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Watts is watts. There are heaters which retain some heat and distribute it more evenly than others, but it still takes X many watts of heat . "round number" for electric heat is 10 watts per square foot for outside ~30º, then add for outside temp, and insulation. 20 per square foot for zero degrees, add more for poor insulation. This is just seat of the pants numbers.
  5. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    The ceiling is insulated, the walls likely are not. The exterior is faced with standard brick, like you'd expect to see on a house. Inside of that is another type of "brick". It's not concrete block, but something kind of like that, from what I can tell. The original owner of the house owned the local brick company at the time. I dont believe there is any 2x4 framework to the walls, I believe it is just plaster over the brick. Furring out the walls isn't an option as that would require extensive work, such as redoing electrical, tile, cabinetry, etc... The floor isn't insulated and again, not much of an option as it is somewhat a finished ceiling in the garage below. The good news is there is a heater that normally keeps the space below at about 45-50*F during the winter, so the cars are kept warm and so things stored in there don't freeze. The floor in the space is original oak flooring, so overlaying over that not much of an option. The windows are original 1915 erra wood, single pain glass windows, but there are very nice custom made storm windows covering them, so that helps a bunch. Ohh, and the ceiling is finished sheetrock, so hanging something from there probably isn't much of a viable option.

    Water not available, nor gas. Neither would be easy to pipe in, considering the driveway was just repoured last year and over half of it is stamped concrete. The exterior bricks should be very tight as the entire building was tuck pointed in the last year as well.

    I know that takes a lot out of alternative options, so we are left with electricity, but at least what is here is pretty air tight. Luckily the garage is on it's own 100amp meter and there isn't much in the breaker.

    In years past we were able to keep the area pretty confortable with a window ac/heater. On the coldest days, it struggled to keep up, but space heaters made up the difference. The window unit quit working and was replaced with just an a/c unit, with plans to install baseboard or something else for heat.

    So loaded with that, EdenPure, electric baseboard, electric hydronic baseboard or I guess maybe a nice looking panel radiator (suggestions here please), or something else yet?

    It almost souds as if you guys aren't for trying the EdenPure, or am I reading that into the replies?

    jimbo, I understand what you saying. That is why I think some people posted negative replies on the EdenPure, they thought it would give them some sort of miracle heat. From my understanding they use copper coils which are supposed to retain and distribute the heat for longer periods. Same sort of logic as the oil-filled/hydronic electric baseboards. Question is, does it really work well... They say up to 1000sqft for the $400 unit, but the watts don't add up. My thought is if even it provides half of stated heat for this room, it should do it's job. "IF" being the key word!

    Thanks again...
  6. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    Figuring the R-value of this building is a bit tough. No it doesn't have any traditional insulation in the walls that I know of, but I would think 2 layers of brick and then a layer of plaster would give a decent figure. I'll have to go look and see what I can find. It sure has to be better than the R value of a 2x4 house with sheating and just drywall.... Doesn't it??
  7. Dana

    Dana In the trades

    Messages:
    2,837
    Location:
    01609
    If the finished ceiling in the garage can take the weight, you can blow insulation between the joists. 400sf of uninsulated floor over a 45F garage is a huge heat loss. Blown fiberglass would give you the better R value per-lb, but cellulose will slightly outperform it due to higher resistance to convection within the insulation layer (less of an issue in a floor than a ceiling, to be sure.)

    The R value of a 4" brick is about R0.5. You have two wythes, call it R1. If it has a 2" cavity between the wythe's, call it another R 0.75, bringing it up to R1.75+ whatever plaster & lath (if it's ca. 1915 horse-hair plaster on lath, it's probably R0.5-ish, less if it's blue-board & hard plaster.) R2-2.5 is about all you get, and that's if it's a cavity wall. R1.5 is more typical if the wythes actually touch.

    An empty studwall with wood siding has about R1-1.5 in siding + felt + sheathing, the cavity is another ~R1, then it's whatever the interior finsh wall is. It's slightly more R than masonry cavity wall, but not enough to write home about. They're more prone to air leakage/infiltration losses, and have no thermal mass to speak of. At equivalent R values masonry walls are somewhat more efficient, buffering the diurnal temperature swings due to the thermal mass, and leaking less air.

    Watts is watts only when you're looking to satisfy the thermostat. Radiators will always be more satisfactory to humans than convectors at equivalent power levels. The bigger the heating load, the more pronounced that sensory difference becomes. Don't know (or care) squat about EdenPure, but I do know from radiation vs convection heat. I can't imagine that they've got an advantage over any other mini-radiator/convector system in a pretty li'l box, and it'll SUCK compared to a Z-mesh floor from a "cruisin' in yer socks" comfort point of view at 67-68F room air temp.

    If you wanted to hang a radiator panel from the ceiling you'd have to anchor it to the joists, not the finish surface but it should be possible. If you put radiator panels next to the uninsulated walls, a bit of radiant-barrier (sheet aluminum will do) between the panel and the wall will keep the wall from heating up the great outdoors. (Radiant barriers need air gaps to work- both sides preferable in this application.)

    If the storms are tight, they'll outperform a middle-of-the road double-pane window. If you have more glazed area than you need, snug fitting removable insulating panels can be fashioned out of rigid-board foam. Half or 3/4" iso is nice & light, and will cut the heat loss out of the window + storm by ~75%. (cover 'em with fabric if you want 'em to look nice.) They stack & store easily, if you want to use them only seasonally. Adding a set of interior storms made of polycarbonate will cut the heat loss of the windows by about a third.
  8. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    Calculation

    Brian

    Since it is heating you are concerned with it is an easier job to calculate the losses than for cooling. Take all the individual R values of the each material and add them up for each of the walls, roof, floor or glass. to get the R total

    R total=R(brick)+R(sheathing)+R(Gyp) Note: to simplify I have ignored the air film resistance, air gap resistance, etc.
    Than U(overall heat transfer coefficient)=1/R total for the wall, roof, floor or glass.

    Wall...Q=UA(deltsT)
    Roof...Q=UA(deltaT)
    Glass...Q=UA(deltaT
    Floor...Q=UA(deltaT)

    Orientation is not a concern since it is heating.

    Plug the value for U for each of wall, roof, floor and glass into the equation Q=total heat loss (btuh)=U*A*delta T, where A is the area of the wall, floor, glass or roof and delta T is the temperature difference between the inside and outside temperature. Out side temperature being design temp for Kansas city probably 2 degrees F and the inside design temp should be aroun 68 degrees F resulting in a difference of 66 degrees F. Add all the Btuh up and that is the raw heat loss for your structure. Add 30% for warmup and you should be close.
    Add insulation if you can because brick, wood, etc does not have much of an R value
    8" Brick is about R=.4 which with out sheathing or any other material is which yields a U=value of 2.5 (from the equation above). As an example compare it to R=11 which yields a U value of .091 which is much better
    (less heat transfer).
    Just for grins, you might want to compare added insulation with as it is now and see the difference to make a determination if it is worth it or not.
    Respectifully Dave
  9. Dana

    Dana In the trades

    Messages:
    2,837
    Location:
    01609
    That's a pretty crude model at best (not 'xactly Manual-J or IBR, and methinks you have the R value of double-wythe red brick confused with 8" cinder-block) but at least this one lets you play "what if" pretty quickly:

    http://www.builditsolar.com/References/Calculators/InsulUpgrd/InsulUpgrade.htm

    KC is a fairly mild 5400 heating degree-day climate, but peak heating loads determine the total power needed, and 2F design temp close enough.
  10. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    Calculation

    Dana
    I quit using long hand calculations years ago, (they went out the door with the drafting board) and do very little residential by choice (something a good HVAC contractor can do better than I). Now I use a program called elite or Trane trace (for energy calculations) more for commercial projects. They typically have a U factor calculator embedded, as I think you are probably know.
    Irr-regardless of how "crude" it may appear it gets one to the answer without having to go thru the manual J approach or some other hand calculation.

    I though it was said that there were two layers of brick if incorrect thanks for the correction.
    The approach is correct based on assumption made. The determination of the load is left to Brian if he wants to tackle it. Basically the R values are table lookup based on the materials, density, etc.
    Thanks for the verification of the OSDT.
    Sincerely Dave
  11. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    Can-O-later

    85 degree air for free on a 40 degree winter day

    [​IMG]

    [​IMG]
  12. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    gator37, you are correct, there are two layers of brick. One is what I'd call a standard brick used to face a house. The other is more of a building brick used for structural work back in 1915. Not sure what technical term for either is, but not sure it really matters.

    I'll play with energy calcs when I get a chance and maybe figure it's worth while to insulate at a later date. For now, I doubt that happens. The floor is the only really cost effective thing that can probably be insulated, but I doubt that happens any time soon. The ceiling under the floor is that old fiber board stuff and there are lots of wires, etc running under it. To do the job correctly, that ceiling should probably come down, be insulated, then a new drywall ceiling installed.

    Still not really sure what direction I'm going, but at least you guys have given me some things to consider.

    What I'd really like is to place a nice pellet stove up here, but it's not my house, it's my parents and they don't want to mess with carrying the pellets up/down and cleaning it out.
  13. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    heat loss measurement

    Rent a heater that puts out 12,000 BTU/hr [from fuel] and see if holds the room temp at a reasonable level.
    Knowing inside and outside temps. you can calculate approx. R-value.
    Then recalculate for 97.5 cold temp percentile value.
  14. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    Correction

    Brian
    The approach is correct but I did read a wrong line for the R value as Dana indicated.
    It should have been R=1.6 for 8" of common brick on my chart which would result in U=.625 BTU/(HR-DEG.F-SF). The difference is still great when compared to insulating material.
    Sorry about that just got rushed.

    I remodeled my storage area above my unconditioned garage Dec of last year changing it to an office with a toilet and sink. I put in a Trane heat pump (thru the wall type PTAC unit) with 2KW aux heat but I added R-11 all around walls, floor, ceiling. The conditioned area was ~400 SF. I have one window which about 3'x4.5' (single pane not insulated) which is vastly different that your situation.

    Note my worst case outside design temp is ~11 deg F (North Alabama) which is quite different then your OSDT of 2 deg F which makes a significent difference. Also I oversized a little because I want to be cool after working outside I will sacrifice the dollars for instant comfort. I think my unit is about 15000 BTUH.
    I would not recommend a heat pump for your area.
    I also entertained the idea of a pot belly wood burning heater and probably will do that the next time I get the roof redone.
    Dave
Similar Threads: heating garage
Forum Title Date
HVAC Heating & Cooling Heating Basement & Up satires Should you separate heating systems Sep 1, 2014
HVAC Heating & Cooling What size heating strips Jun 13, 2014
HVAC Heating & Cooling Intertherm E2EB-017HB - Heating Element Stays On Jan 20, 2014
HVAC Heating & Cooling Help with choice of Heating/ Cooling equipment for Southern New England Jan 11, 2014
HVAC Heating & Cooling Weil-McLain GV-4 Overheating Dec 27, 2013

Share This Page