Slant/Fin Heat Loss Express Questions

mosley

I am using the Slant/Fin Heat Loss program to calculate the heat loss of my house and have a few questions.

1. What is the "Factor" the program refers to? I thought it was the U Factor (inverse of the R Value), and my calculations agree with Slant Fin's calculations for the Door & Glass, Ceiling and Floor heat loss. But my calculations do not agree with Slant Fin's Exposed Wall and Cold Partition heat loss calculations.

2. What is the Infiltration Factor? Where can this infiltration factor be found or calculated? I recently had a bower door test performed and know my CFM50, would this help? The only two mentions of Infiltration factor are these:

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-perform-heat-loss-calculation-part-2

https://www.uponorpro.com/~/media/Extranet/Files/CDAM/CDAM_Manual_7thEd_0711_Ch7.aspx?sc_lang=en

3. My basement is heated. Where to I factor this into the program?

4. What do I do with closets and hallways that do not have exterior walls? Do I just add them into one of the adjacent rooms?

EBEBRATT-Ed

My Slantfin version is old so take what I say with a grain of salt. Someone will confirm or call me a liar

1. With my version you can click to open different factor from which to choose, type of construction, insulation, single pane or storm windows etc.
2. I think they calculate the infiltration factor base on sq footage or linear feet of exposed wall. I remember they ask windows and doors on opposite walls etc or on the same walls. this is how they calculate infiltration
3. Figure the basement as a separate room or rooms.
4. Yes add closets and hallways to the adjacent rooms divided up as best you can

Someone else will chip in, I know this is not the best discription

bmwpowere36m3

I just went thru this recently… What are you trying to figure out with the heat loss? Boiler sizing, radiator sizing, just curious?

1. Most of the "factors" in the software are U-Factors. In my case, 2x4" walls & R 15 insulation, the exterior wall U-Factor was spot on. The wall isn't 100% covered in insulation; they assume about 85% insulation and 15% studs, which have a much lower R-value.

The cold wall partition u-factor is also correct. They assume the temperature is slightly higher than outdoors (design) on a cold wall. So they fudge the u-factor a little higher than actual.

2. For infiltration I found the factor 0.009 = 0.5 ACH, 0.0135 = 0.75 ACH, 0.018 = 1 ACH and so on. If you have the CFM50 measurement, then you need to divide the volume of the conditioned space by the CFM50 #. That gives you ACH50, which you then need to convert to ACH: https://www.energystar.gov/ia/home_improvement/home_sealing/ES_HS_Spec_v1_0b.pdf

The tool calculates the volume of the room and heat loss via infiltration based on the "ACH factor"

4. Basement, are you interested in the heat loss of the basement or what is the heat loss thru the floor of the 1st story? If the basement is the same temp as the 1st story, then there is no heat loss thru the floor of the 1st story.

However there is heat loss thru the walls and floor of the basement. Sounds like the basement is conditioned space, so you should calculate its heat loss like any other floor/room you're doing.

4. That's what I did, since in my case there is still heat loss in those areas thru the ceiling, floor and infiltration.

Rich_49

call whomever performed the blower door and tell him you need 50 converted to Nat . you need CFM50 converted to ACHnat

Tom_133

@mosley If you download slant fin on an iPad or iPhone, just click on the part you want described. It actually does a good job breaking it down as to what you may have in the building you are trying to get the loss in. In fact if you do rooms with the same conditions it will remember room to room, things like heated above or below it goes pretty quickly

Robert O'Brien

Why not use your actual fuel consumption to calculate a real number rather than making guesses to get a calculated number?

mosley

Thanks to everyone for responding. I was considering radiant heating and was told the first thing is to determine the heat loss of the house. My house is 2 stories, and a 7' basement (5' below grade).

1. With my version I too have the drop down box to select the Factor depending upon construction. But I chose to determine this number myself. For instance, assuming the U factor of my windows is 0.3, I know the following:

Q = Area * U factor * ΔT = 87.51 sq ft * 0.3 * (70-10) = 1575 BTUs

I get the same value from the Slant Fin program and my calculated values are also the same as Slant Fin's for my ceiling, floor and infiltration.

To calculate the heat loss of the exposed walls of a room I first determine the U factor of the exposed wall by adding the U factor of the sheetrock, insulation, sheathing and shingles.

Q = Area * U factor * ΔT = 235 sq ft * 0.07 * (70-10) = 987 BTUs

Slant Fin is telling me the heat loss is 618 BTUs, and my calculations for Cold Partition walls are also different that Slant Fins. What are they using to calculate the heat loss? Is there a Frame Factor or something?

2. I calculated the infiltration factor the following way:

CFM50 = 4341 (from blower door test)
ACH50 = (CFM50 * 60 minutes) / Vol = 4341 * 60 / 22159 = 11.754
ACH50(nat) = ACH50 / N factor = 11.754 / 14.8

Since I know the infiltration factor is 0.018 for ACH(nat) of 1, I divided my calculated ACH(nat) value by 55.56 to get an infiltration factor of .0143. Is this right?

3. I think I was doing a few things wrong. First, the ceiling and floor factor of my 1st floor should be 0.0 because they floors above and below are conditioned (heated) spaces, correct? And the floor factor of my second floor should be 0.0, and the ceiling factor of my basement should be 0.0, correct? And my basement should have a ceiling factor of 0.0.

Robert O'Brien: How do I calculate this from my fuel consumption?

Rich_49

That ACH number would suggest that you own and live in the tightest building on the planet . Were you able to contact the rater that performed the test ? If he is not able to convert it the whole blower door number becomes questionable.

bmwpowere36m3

1. Are you subtracting the window and door sq from the exterior wall sq when doing the calcs? Using the same u-factor in your hand calcs and S/F?

Cold wall partition, S/F assumes a higher outdoor air temp, then what's entered in the tool. For example, you enter 10* as your design temp and 70* as indoor; thus a temperature delta of 60*. For a cold wall partition is might assume a delta of 35* (I did the calculations a while ago…). So the u-factors in the tool for cold walls are inflated (than actual) on the assumption the temp delta is smaller than the parameters you entered (outdoor and indoor temps).

2. So an ACH of 0.79, sounds reasonable. That's an infiltration factor of 0.0143 in the S/F tool.

3. Yes, wherever the delta t between two surfaces is zero, then there is zero heat loss. I.e., between ceiling/floor of conditioned spaces.

Robert O'Brien

F = HL x 24 x DD / E x P x TD


F = annual fuel comsumption
HL = Heat load (BTU/hr)
24 = hours in a day
DD = Degree days
E = boiler efficiency
P = heating value of fuel (btu/gal)
TD = temperature differential (indoor design- outdoor design)

icesailor

You don't understand how the program works.

It takes a whole wall with no openings, and calculates it with no openings. Then, subtracts the loss for the openings. Some windows loose more than others. With some walls that lack insulation. a triple pane window subtracts loss from the wall. In an insulated wall, the window will subtract the loss.

Inside closets with no exposed wall? No loss. Second floor closet ceilings? Make the room bigger. A 12' X 12' room with a 6' X3' Closet? Call the room 13'6" X 12'.

I worked with a guy that never brought his lunch to the job. One day, he spent 25 minutes trying to con a guy out of a sandwich. When the conned finally gave a sandwich to the Con'er, the guy looked at it and gave it back. The con'er didn't eat sandwiches with mustard on them. Some people complain about a free lunch.

mosley

What I was doing was comparing my calculations to the output of the Slant Fin program. I was getting different values because of two reasons. First, I was not subtracting the heat loss due to windows and doors from the exterior walls in my calculations (thanks bmwpowere36m3). Second, I believe there may be a bug with the software because I was getting different heat loss values for the same exact criteria entered, side by side. That may be due to the fact that I am running the Slant Fin program on a mac (thru Wine).

bmwpowere36m3

I've run very similar calculations through three different programs (SlantFin, Crown excel and load calc) and ended up with variations on the order of 5-10% for the whole house. Most will agree these programs are padded somewhat (15-20%), so a few thousand BTU difference on tens of thousands of BTUs isn't huge in the scheme of things.

icesailor

mosley said:

What I was doing was comparing my calculations to the output of the Slant Fin program. I was getting different values because of two reasons. First, I was not subtracting the heat loss due to windows and doors from the exterior walls in my calculations (thanks bmwpowere36m3). Second, I believe there may be a bug with the software because I was getting different heat loss values for the same exact criteria entered, side by side. That may be due to the fact that I am running the Slant Fin program on a mac (thru Wine).

Throughout many years, I bought and tried many computerized heat loss programs. Not one agreed with any other. They all use different methods.

Slant Fin is based on the IBR hydronic method, developed many years ago by the IBR/Hydronics Institute in conjunction with the University of Illinois, Champagne/Urbana. They used their research and methods to teach thousands of heating installers an accurate and dependable method to calculate heat loss and design heating systems. Until the IBR/Hydronics Institute folded, there was never any Windows based heat loss programs that were Hydronics heat only. They were all ACCA based Air Conditioning based within a DOS Shell, with heat as an aside.

If you took the IBR/Hydronics weekend course, it was explained how the program worked. It was all done with instructional books and workbooks with plans.

IBR had two methods to figure heat loss. The "Detailed Method" which required vast amounts of measurements and more calculations. Then they developed the "Modern Method" where many calculations are either taken for granted and rolled into factors, or just plain changed. They advertised that both methods came out with the same information. They did. But if a room called out for 19'3" of baseboard, you were going to install a 8' length and two 6' lengths for 20'.

There's nothing that your not fully understood heat loss program that doesn't compare to the Heat Loss Explorer program won't solve by ignoring the more complex program in favor of simplicity. The ASHRA and other such programs are designed for really smart people. Those people need to take a year off and earn a degree in heat loss engineering. For those of us with less skills, we just had to figure out how to do it, and do it. And it always worked fine until someone came along and started to fix something that wasn't broken.

Ones that worked on Windows 2000 or Windows 95 worked differently that the one for Windows 7. Especially buildings with additions and new windows with old parts. For the ease of it, I broke it up into different complete buildings, then calculated it as one, then the other. Then modified it as needed. You could get the IBR/ AHRI H-22 heat loss guide and the #240 advanced piping design book back 4 years ago from them. I lost all that stuff when I moved. I tried to get it from them again. The only thing I found was that they might have sold all the course to someone and he wants to make money teaching the courses. It became not important to me.

It was faster and easier to do it right out of the book. The computer program just gives you a nice printout with the same numbers.