In modern construction where people do care about proper building, I still see the use of R-19 or R-21 fiberglass being used all around here while blow in cellulose is in the attic.  When sparking conversation with builders, they seem to believe a.) more heat it loss through the attic because "Heat rises" and that b.) extra detail / quality insulation (rock wool) does not pay for itself because of "diminishing returns".

I ran calculations online with a rectangle 30'x40' with 8' ceiling height.  It appears all these calculators just go by the exposed surface area and what the R-Value is of that surface area so there is no possible way for me to tell if this is proper or not for my cost analysis of insulation. 

Are there any solid, physics based calculators online? 

In my mind a new home that is carefully built has a very low air exchange rate.  No leaks from windows and doors, and few leaks with framing.  This would mean insulation is the next defense.  It seems R-19 versus R-30 in a wall is about a 1,300 BTU Loss difference on a Delta of 70 degrees. 70 indoor, 0 outdoors.  To me, that doesn't seem like a lot. Considering a Heat pump produces roughly 3,600 BTU / kWH this means every 3 hours 1 KW more is used/spent for the difference of R19 instead of R30.

This is a broad topic with many bases, but I want to open it to some knowledgeable opinions and input. Are these older style older aged contractors more the wiser to continue that method and scoff at the BTU savings and IS there any truth to more heat escaping an attic since it is (I believe) always going to be more square footage than the surface area of a wall as long as the wall stays at a standard 8 foot?

Or are the online calculators accurate in suggesting each surface area exposed loses equal BTUs and that heat escapes each surface the same?

Attic insulation is less expensive per R value - so using more there has the same ROI. In the summer, the attic/roof is typically warmer than the ambient air. So some boost to ROI from this too. There is also a small difference due to Winter stratification (room is hotter at the ceiling).

Consider using BEopt software.

Posted By jonr on 23 Dec 2016 12:24 PM
Attic insulation is less expensive per R value - so using more there has the same ROI. In the summer, the attic is typically warmer than the ambient air. So some boost to ROI from this too.

Consider using BEopt software.

So you are suggesting the use of more attic insulation is beneficial because you are patching more BTU loss at a cheaper quantifiable mount (cost of product and labor per ceiling vs. wall)...correct? 

Yes, typically. But it's not always true. For example, once you decide to build a double stud wall, the incremental cost for more wall insulation is pretty low.

Makes sense. So in a standard low tech build of a basic 2x6 studded wall the builders add in extra insulation to the attic to compensate for the lack of insulation in the walls to end up with a fairly low BTU use home at an easy and quick labor perspective. A double studded wall would be easy with cellulose fill. If only the "wet blown" options were available here versus mineral wool batts or just simply dry blown cellulose.

In FL, the older concrete block houses had NO wall insulation, but did have R-19 or so in the attic. Considering that the attic could be 130 degrees or more, versus an outside air temperature of 95, it would make sense to have more insulation in the attic. Winter is too mild to worry about, for the most part. In a heating climate, it gets muddier. My attic here in SC is generally warmer than the ambient outdoor temperature, especially during the day. In the winter, I'm wasting that heat, but I assume it's more than compensated for at night when the attic is cold.

It is an interesting discussion. Every insulation requirement I've ever seen calls for more in the attic than in the walls. I'm not sure why. I imagine that on a cold night, my attic is probably warmer than the ambient temperature, if only a small amount, yet I have much more insulation separating it from the the living space than I do in the walls. It does help during the cooling months when the sun is beating down on the roof. On my front porch, I can feel the radiant heat during the summer coming through the ceiling.

Any recommendations on a calculator that will allow me to determine the daily cost to heat based on insulation, HDD, price of fuel (electricity) and type of heat?

Where are you?

I'm one of those "older aged contractors", building "modern construction where people do care about proper building". For most of my nearly 45 years of building, "proper building" has been difficult since there was a scarcity of good data and analysis about exactly how to do that. That changed with the publication of Joe Lsiburek's (Building Science Corp) "A Comprehensive Guide to the Best Cold- Climate Building Techniques" (and five other versions for other climates) and the formation of Passive House Institute US (PHIUS) which brought real world knowledge of the world's best building practices to America. Now, since there is no excuse for ignorance, we now build net zero energy ready houses, with rain screen siding details, proper ventilation and about twice "code minimum" insulation. Why? Not because we've figured out exactly how much insulation makes sense given todays HD price for fiberglass batts compared to our propane supplier's current price per gallon, but because these techniques result in a healthier, far more comfortable home with higher resilience to weather variables, and, when combined with photovoltaics, is far less expense over time, and makes good sense.

Some of the dynamics involved effect what would be the most cost effective best practice. How are you heating the space? Forced air? if heating air, with your described 70F inside temp at body level, the delta at the ceiling (2' above the typical head) might be significantly higher than 70F with the hot air stratifying(filling the room from the top down) that is probably the thinking behind the higher code minimum ceiling insulation requirements as most heating schemes involve heating air. A heating scheme like radiant floor which achieves a comfort level without heating as much air ultimately would result in a lower ceiling delta temp and less loss and requirement for insulation there. Of course as mentioned, the barrier between summer attic heat loads is still a necessary dragon to be slayed so more insulation there still makes sense.. If you can gauge the stratification of the space, you can apply those different deltas to the appropriate surfaces to get a little more accurate loss calculation. IE higher temps at the ceiling, lower for the floor and average the differences between floor and ceiling to apply to the walls and window R value/U factor. As mentioned available space and install costs make adding more insulation in the attic space very cost effective and easy.

I think most walls are under-insulated. At R3-R5 per inch, unless you are prepared to significantly alter the structure, the basic thickness of the wall becomes your limiting factor for added wall insulation. As mentioned, once you build a thicker non bridging structure, the added insulation cost to fill it is relatively insignificant over the insulation required for a code spec wall for your region.

The 3600 BTU/KW number you stated is close to the basic conversion number from BTU to KW(it is actually 3412 BTU/KW). IE: that is what you get out of a straight resistance electric heater per KWH of input. A heat pump or heat concentrator as I like to call them, is typically 3 to 5 TIMES more efficient than straight electric resistance heating or 10,000-17,000 BTU/KWH. Your numbers would be close for resistance heating, heat pump heat would use 1/3 -1/5 as much energy at your different calculated R values...

Bob I - Nebraska Climate Zone 5.
Hope no offense was meant by my terminology. It's just that I have yet to meet a less than 30 year old GC here. At my age, currently less than 25, I have not been around a lot of GC's. However, I know my area is saturated with older builders and no new, younger people are taking interest in this low population area. Consequently, houses that are built are just not near as detailed as they could be! A big factor for me is how much performance can I get for each dollar I spend. I also have to take into effect how much this building will cost to maintain, and how much tax burden it will be. I'd go for 1' or 2' thick walls if I was taxed on livable square footage. However in my jurisdiction, taxes are dependent on exterior dimensions and material. Sadly I have to immediately consider (Once again, very sad IMO) the cost differential between a.) More taxes on square footage and b.) More expense in energy. If I save 200 to 300 on taxes a year because of a smaller footprint, and only pay 150 to 200 more in energy due to lack of insulation what am I to do? If more areas would consider that it's good for the environment to have energy efficient homes and not go against the homeowner and say we tax you on the exterior dimensions then this would be a no-brainer for me. Nebraska is notorious for high taxes, however, so I am going to be a minority due to location.

Ronmar - Thanks for the information. I don't know where I read but I came up with multiple sources before that stated 1kW = ~3600BTU. So, that's music to my ears to hear that's my toaster oven and that my heat pump is even more. I have read heatpumps are considered "200%" efficiency, while electric forced air furnace is 97% efficiency. I'm assuming it's the science behind a heat pump that allows the bold statement of "All heat pumps are roughly 200% efficient". Current and future house I have would be all electric heating/cooling. I definitely agree wall thickness is a limiting factor. It's also always less surface area than a ceiling assuming 8' high walls. As earlier stated, I would love to go 1 or 2' thick on walls but floor space efficiency also has to be scaled in.

No, I'm not offended. Unfortunately there are lots of older builders who insist on making the same mistakes in judgement they've made for 40 years, which the buyers of their homes get to keep. Many of the standard practices that we've all used for years are poor practices that could be improved without a lot of expense; they want to build as they've always built - which is generally crummy. But builders that want to build good houses, and homeowners who want good houses, pay attention to the details. There is a huge nationwide problem now with younger folks not getting into the trades, so all of us are getting older with fewer replacements coming up.

Keep in mind that "code" means "this is the crummiest house with the least insulation we'll let you build". It is NOT a recommendation (as many folks think) for good building. Your argument that losing 8" of indoor space isn't worth it (I'm comparing a 2x6 wall to the double stud 10" walls we sometimes build (other times it's 12"), seems hugely shortsighted; especially if it means that you'll be less comfortable and have more heat loss as a result. Look at your house with a longer timetable - you're 25 so you might conceivably live in the house for another 40-60 years; do you really want to do that thinking "if I had only..."?

A house with low expenses is usually the least expensive house long term. And Air Source heat Pumps have efficiency ratings in the 200-300% range - they can do that because unlike gas, oil or wood sources, they aren't converting anything to heat. Rather they use a refrigerant cycle -they're basically a larger version of your refrigerator, so the refrigerant gets pumped back and forth and delivering heat or cooing to your house. They're also quite inexpensive to buy and install, and they run on sunbeams, which, unlike gas, oil or wood (usually) are free. (You would need to pay for solar collectors)

you might conceivably live in the house for another 40-60 years;

Or only for four years. Which will make a huge difference in your ROI on various upgrades.

if you're only going to live in it 4 years, rent and save the bother

We built on a shoe-string budget, but managed to build ICF. I don't know if it will ever truly return the extra money spent, but the comfort is worth it to us. After a lifetime of living in drafty, poorly insulated homes, the difference is truly amazing. I believe that you can keep the thermostat lower if every inch if the house is the same temperature, rather than having cold spots in the winter, or hot spots in the summer. Good insulation and tight construction is more than just a monthly power bill. Of course, at your age, you don't feel the cold like I (at 63) do!

There is a way to determine the exact difference in cost. I designed our HVAC with a $50 computer program. It was very detailed, and you entered all of the factors for every room of the house. It would be easy to use a similar program and compare the results as you change R-factors, window sizes; even exposure. It would spit out the BTU's required for heating and cooling, and you could then plug in the cost of heating and cooling that number. I didn't take it that far, but I can say that the calculated BTU loss seems to be very close to the real-world results. Our HVAC performs exactly as predicted, and the cost (mini-splits) is amazingly low. Another factor is the change in utility costs. The insulation you buy in 2017 is never going to change in price once you've bought it; the energy you buy will likely go up over time. I know of NO way to predict that, though!

We have free software on our website that can be used to accomplish the heating performance cost analysis that you desire:

Borst Integrated Heating System Performance Software

In order to use it, you will need to know your total building heat loss in Btu/hour-deg F and your heating degree days. You can get the former by using our free heat loss analysis software or some other equivalent software:

Borst Heat Loss Analysis Software

Borst Existing Building Energy Usage Analysis Software

Please rest assured that proper math and physics have been used in all our software.

As Bob pointed out there is no excuse. Back in the day there were not as many computer tools but we managed, some lucky guessing, some experience. Today most are coming to these "green" sites for a cheap fast easy answer relying on someone with little knowledge not even a location many times to tell them how to design complex building science. An impossible task. You can see this by the low traffic on software sites.

Today, free accurate energy & financial models from the DOE and NREL like BEOPT with proven tested builds and climate files are available in most USA climates & world (25 in NE) your tax dollars paid for. This one does heat transfer only, multi-zone, no hygrothermics..to perform that passive criteria per PHIUS has to met in WUFI Passive first. Beopt is pretty straight forward, WUFI is not but it has no competition.

In center NE for a 2280 SF slab-on-grade w/ 580 sf up I'm showing ~900/yr utility bill saving's for a ~2015 IECC min home compared to a 2009. A 12kW PV drops bill to $294(black bar) , net zero around 15kw . All electric design client wants gas stove has drastic HVAC cost reductions and loads, minisplit sizing @ max cooling load ~ 2.5 ton 5 zone.  

I'm still optimizing this for a client different location but you get the idea. You can see the annualized economic inputs all kinds of reports are generated. I can compare as many designs as I want easy peezy to optimize and there is a mode for that. 

All software is only as good as users. NREL/BEOPT/Energy Plus engine & WUFI/PHIUS are at the top.

More PICs

I can save this client ~$200/yr in utility by loosing the open below/vaulted great room and beautiful exposed trusses & dropping the 10' walls to 8' but some are willing to pay the price for aesthetics...It's not always about energy saving's & comfort. They want all metal siding and roof hard to deal with but I got it done.

I'm going to play with BeOpt actually. I think I got a good idea with using http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

It allowed me to calculate the BTU Loss per different wall insulations. Although it's not as accurate and has some left out details, it will show the difference in R Value and cost savings. Looks like some of the energy grants are closing end of this year unfortunately. Solar is a whole different ball game. Currently I am looking at 2x6 with 5.5" mineral wool, 2x8 with 7.25" mineral wool, or double 2x4 walls with .5" to 1" between them to gap the thermal bridging but maintain a small foot print on an already smaller house. I'd use cellulose there, but looks like it'd just be the dry packed not wet dense packed here.