How to figure heat loss calc on brick veneered 1950's house?

Steamhead (in transit)

is block walls with brick veneer, and furring strips holding wire lath on which the plaster walls are built. It was built in 1957, and unfortunately has scorched-air.

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stacey

How to figure heat loss calc on brick-veneered 1950's house?

Hi and thanks for this very helpful web site. We just bought a new house and are having trouble with the heting- we're also looking at buying a new boiler, so we would like to do a heat-loss calculation. I found a quickie free program on line and I am trying to fill it out, but am stumped as to what to choose for wall construction. The exterior is built of colored concrete "bricks" and the interior is drywall, but the walls do not seem thick enough to have 2 x 4 construction: probably just furring strips and drywall. The house was built in 1956 so we do not believe there is much, if any, insulation. Can you advise on what construction type most closely matches this in the heat-loss-calculation programs? Also- do you know a good, free on-line calculator? Slant-fin's program does not appear to be on line. Thank you!!

Steamhead (in transit)

It would depend

on whether the walls are just brick, or concrete block with brick veneer. If you're using the Slant/Fin program, these options are under Exposed Wall Factors for each room.

It might be possible to inject some sort of foam between the plaster and brick/block. Consult an insulation contractor for more info.

I don't know of an online-based heat-loss calculator. The Slant/Fin program can run on any Windows computer (I've even run it on Ubuntu Linux under WINE) and is a pretty painless download if you have a broadband connection. If you still have dial-up you can order it on CD.

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Big Ed_4

50's Construction

I always found they used 2x4 construction with the insulation tucked in ...But your there and I am here.

Worst comes to worst you can do a heat loss the old fasioned way and take out a book from the Library. Take out the book " Modern Air Condition and Refrigiation " turn to page 1050 or 1150 there is a simple heat loss and heat gain calculation you can use . It would take ten min if you have all the measurement ready. Gross windows and type ,square foot door and type , skylights ,net outside wall and R value , ceiling type square footage and R value, square footage over vented or nonvented space and cubic footage for infiltration ..

You may find they don't make a boiler small enough to meet your need. I have found this for most avagage homes .Remember you need to size the boiler to the largest load which most likely your hot water needs , if your using your boiler to heat up your hot water.

Big Ed_4

True

Come to think of it I remember a develoment of small slab ranches with single casement windows....

I guess depends if the carpenters or masons bring in the cheapest bid

stacey

Thanks guys...

I looked in the attic and the roof is being supported by the "brick' section, not by 2 x 4 frame construction, so I gather it isn't simply a veneer over regular stick-built type construction, like we originally thought. I do not believe there is concrete block in there, though. The walls don't look thick enough. How would I know for sure?

Steamhead (in transit)

Measure the depth of the wall

if you can get at it. This could be done from a door or window opening. The Slant/Fin program gives depth options of 4, 8 or 12 inches for brick, and 8 or 12 inches for concrete block or poured concrete.

If you can see brick rather than block on the inside of the wall, you know what you have.

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mark schofield

go to a window a place a straight edge horizontally along the face of the outside brick and have one end of it go past the frame and past the edge of the window opening. do the same thing on the inside and measure the dimension. make sure that the straight edge doesn't angle out due ti the exterior and interior trim (brick mold). if a brick is 3.5" wide and Sheetrock is .5" and furring strips are .75", an uninsulated wall of only brick should be about 5". If there's allot more than that. I'd go into a closet on an outside wall and cut a hole in the Sheetrock to see what exactly is going on. Mark S

Uni R_2

Is this natural gas?

n/m

Brad White_203

U-Factors and R-Values

Stacey, I am not sure if the program you are using wants inputs of U-factors (BTUs per Hour, per SF, per Degree F. difference), or the R-Value which is the inverse of the u-Factor.

You want the u-factor to be lower, the R-value to be higher, you see.

I calculate for an uninsulated stud wall with brick veneer, a u-factor of 0.2383 (which corresponds to an R-value of 4.1964).

If the wall cavities are insulated with 3.5" fiberglass batts, this will improve to a u-factor of 0.0879 (which corresponds to an R-value of 11.377).

(These all presume a 25% framing percentage, just to give a ratio of "wood to insulation". Your actual may vary. More windows means more framing and even less insulatable wall, another way that windows hurt heat loss!)

Now, the reality is, you may be somewhere in-between, with thinner rockwool batts or some other nominal form of insulation, I have no idea. As Big Ed said, you are there and I am here. (Not with Big Ed though.)

So, what does all this mean?

If you have 1,000 net SF of wall at the uninsulated number and it is 70F indoors and 0F outdoors.

The original construction, uninsulated, would lose 16,681 BTUs per hour (BTUH).

When insulated, it would lose 6,153 BTUH or 36.7% of what it was for just the walls.

A typical house would have the walls represent about 25 to 35 percent of heat loss. Glass, roof and infiltration making up most of the rest.

I am not suggesting you give up, but you can figure it both ways, insulated, uninsulated and maybe "one in the middle" to bracket your calculations. (Will not take much time).


You might well find that your insulated versus uninsulated wall ( spread of about 10,530 BTU's per hour one to the other), may not affect the boiler selection you seek.

Doug_7

Calculate the R-Value of a Wall

There is another method to calculate the actual R-Value of a wall, when you do not know the interior construction.

You do this in the winter by measuring three temperatures.
- outdoor air temperature
- indoor air temperature in middle of the room
- inside surface temperature of the wall

You can measure the temperature drop across the inside wall air film and from that you can calculate the R value of the wall using the inside air film coefficient as per ASHRAE. The 0.68 inside air film resistance is a constant and is quite accurate.

Here is the equation:

TD/td = R/.68

TD = the difference between outside air temperature and the inside air temperature in degrees F.

td = the difference between the inside air temperature and the inside wall surface temperature in degrees F.

0.68 is the inside air film resistance that governs the rate of heat transfer from the room to the wall.

Do the math and you have the R-value of the wall.

The larger the temperature differential between the inside air temp and the outside air temp, the more accurate your answer will be. Measure wall interior surface temperature at several locations.

Another source that provides a chart is:

http://www.professionalequipment.com/content/how-to-determine-r-value.asp

Doug

Brad White_191

Very handy, Doug

Thanks.