One question I get asked often, and do not have an answer for is what is the percent return in general for insulation upgrades? Say from minimum new code of R 30 (in my area even on Energy Star homes) to R 44 or R 49. Or for an older home with basically no or very little old insulation to R30 or R38. Is there a general rule of thumb? I have had people claim they have done it and saved 25%. But I have no hard numbers. I realize much depends on the home and it age and general construction, but there has to be some general (true and realistic) numbers that people can go by.
On which part are they saving 25% on? As a whole, if you took the house and did have it tested out and did the recommended work, yeah then you could claim a certain amount has been saved because we did x,y,z.
The entire house should be looked as a whole and not just an individual aspect. Everything from the landscaping, to orientation, to appliances, homeowner habits, electrical, hvac, square footage, design, style, age and much more.
You can’t put in new windows and still have unattended air leaks in the house and claim to be saving.
The best is to have it Blower Door/Duct tested and Infrareded (is that a word?).
The easiest thing anyone can do in my opinion, is to weatherstrip, caulk, air seal and insulate. Provided of course people know where to put it. And for it to be done properly, if not it’s a waste.
Check into taking a BPI or HERS course in your area. That’s where the game is nowadays. If people don’t they are going to be out of the loop.
Anyway, back to your numbers. People like Oak Ridge National Lab. have done extensive testing and that’s one place that general numbers come from. results do vary. Check back with those you’ve spoken to and see what type of testing they’ve done.
I am talking about a percent return on adding R value to attic period. I understand the concept that there are other areas to possibly improve. That was not my question.
Adding insulation in the attic is relatively easy to do around here. People ask “if I go from R30 to R44 in my attic what will I save?” They want to try to understand the ROI for the cost of the upgrade. Personally, I suspect it is small and not worth the cost of the upgrade for most people that may not be planning to live in a house long term. But I have no hard numbers to go by. My question was - is there a place out there that has numbers about saving for attic insulation upgrades on a R value basis? At least in general terms.
For a very basic rule of thumb you could use the following heat transfer equation.
It just gives “perspective” to what is going on.
Q = U * A * Delta T
U is the R-Factor inversed, so; R-19 = 1/19 or .053
The U value of R-30 is .033 and R-44 is .023.
The other factors remain the same.
So you have about a 1% change in btu transfer reduction.
You can not change the heating bill by this amount because 100% of the bill is usually not just for heating.
Delta T = 70F inside - 30F outside = 40 F Delta T
A = 1,000 sf of ceiling area to insulate
Delta T * A = X
40F * 1,000 sf = 40,000
X * U = Q
40,000 * .033 (R30) = 39967
40,000 * .023 (R-44) = 39977
Q1 / Q2 = % change
39967 / 39977 = .9997%
A rule of thumb answer may get you in hot water especially if you ignore all of the other facors (it’s like asking how much faster can I run if I buy these track shoes?). Unless you have credentials, the correct answer is that you don’t know or are not qualified to predict as there are many factors that will influence the ROI and a complete energy audit is needed to provide specific ROI guidance.
Excuse my ignorance on this please, but what’s the point in blower door with IR imaging?
Hi Mike…that’s a good link…thank you…!
I could use that often here in the valley of the sun.
Blower door will detect air leaks. IR is will show missing insulation, caulking and such. A regular IR certified inspector can explain it better.
Yes, but don’t both reach the same conclusion?
The blower door helps to visualize leak areas by increasing the flow through the leaks. More flow = more temperature variance = increased visualization of thermal anomalies.
Some areas will be only visualized with a blower door and depressurization of the structure.
The reason for the blower door is to overcome the natural pressures of the structure (stack effect). At any given time a building has positive and negative pressures and a neutral pressure somewhere in the middle of the elevation of the house depending on construction. Exterior forces such as wind, change the location of these forces within the building envelope from left to right and up and down.
The blower door used under 50 Pa pressure/depressurization has the same effect of a 20 mile an hour wind blowing on the house from all directions.
If you use a thermal imager with a blower door you can see air infiltration as well as thermal anomalies such as inadequate insulation. Without the blower door some of the air may be leaving the house and some may enter the house. If you’re not in the right position with your camera, you’ll miss a lot of issues. If you’re inside the house, you see air infiltration but you’re less likely to see exfiltration (due to the thickness of the wall and insulated wall cavities) and vice versa on the exterior.
A thermal imager is utilized to document the conditions during the test, whereas using chemical smoke and similar devices may detect air movement but you must describe their location and it is difficult to identify the extent or the source.
It is not necessary to have a blowout or to generate negative pressure in the building. There are other devices such as your dryer or HVAC system which can depressurize the building and overcome the stack effect. 50 Pa is not required for thermal imaging to work, it is a standardized pressure for testing. Some links may not occur at lower pressures, but then you don’t need to find all of the leaks.