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Adding Insulation for Energy Efficiency part 2

The last time we checked in on the topic of insulation and insulating a house to the point where it wouldn’t need a furnace was back in December. Sheesh. The cold has broke here in the northern great lakes region, and while there is still a chill in the air some days, we seem to be headed right into spring. The good news is, insulation is not just a winter topic. Good insulation in your home will help keep it comfortable all year long. And keep your energy bills down. And so we forge ahead with adding insulation for energy efficiency.

Previously, I walked through the calculations to determine the payback period for adding insulation. Today let’s look at a couple of examples of how that might work our in practice.

  • R-value of the initial insulation (Ri)
  • R-value of the final insulation (Rf)
  • Cost of insulation (Ci)
  • Efficiency of the heat system (E)
  • Cost of energy (Ce)
  • Number of Heat Degree Days for the year (HDD)

And the equation looks like this:

P = (Ci * Ri * Rf * E) / (Ce * (Rf – Ri) * HDD * 24)

OK, take a deep breath. We’re about to do some math!

Example 1: Fiberglass Insulation Upgrade

For our first example, we’ll use the following situation: A house in Wisconsin is going to have its insulation upgrades. It currently has fiberglass batting with an R-value of 13, and will be upgraded to fiberglass batting with an R-value of 19. The cost of the new insulation is $0.41 per square foot. The house is heated by a natural gas furnace that is 85% efficient. The cost of natural gas in Wisconsin is $0.82 per therm, and 1 therm is equal to 100,000 Btu (British thermal units). The number of heating degree days for Wisconsin is 7499. We want to find the payback period for the new insulation.

So, breaking down our equation, we have:

Ci = $0.41 per square foot

Ri = 13

Rf = 19

E = 85% = 0.85

Ce = $0.82 per therm = $0.0000082 per Btu

HDD = 7499

P = (0.41 * 13 * 19 * 0.85) / ((0.0000082) * (19 – 13) * 7499 * 24)

P = 9.7 years

Wowza! That’s more time than I was expecting. So what are the key factors here that could cause this to payback period to go down? Well, first of all, with a little more looking, you might be able to find a better price on your insulation than a quick tour through the Home Depot website gave me. Also, natural gas in Wisconsin is pretty dang cheap right now, all things considered. But as more cities and states do things like ban fracking for natural gas, that cost could go up significantly, which would obviously bring the payback period down.

Example 2: Sprayed Foam Insulation – How much can we get?

What if instead of replacing all that R-13 fiberglass insulation with R-19 fiberglass insulation, we wanted to replace it with spray foam insulation?

Spray foam insulation has an R-value per inch of foam thickness. You can increase the total R-value by spraying a thicker layer of foam. There are tons of options available as far as spray foam goes, but for the sake of this example, we will use this Dow Froth Pack as our insulation. This spray foam provides R-6 per inch of thickness, so 1 inch has R-6, 2 inches has R-12, 3 inches has R-18, so on and so forth.

In this example, instead of calculating the payback period for the spray foam insulation, we’re going to see how thick of an insulation layer we can “afford” to apply, given the same payback period as the upgrade from R-13 to R-19 fiberglass. In other words, we are going to solve for Rf.

So, breaking down our equation, we have:

Ci = $1.01 per square foot

Ri = 13

Rf = x

E = 85% = 0.85

Ce = $0.82 per therm = $0.0000082 per Btu

HDD = 7499

P = 9.7 years

Through the magic of algebra, we can rearrange our equation to solve for Rf:

Rf = (P * Ri) – P – ((Ci * Ri * E)/(Ce * HDD * 24))

Which looks gross, but it’s really just a matter of plug and chug at this point:

Rf = (9.7 * 13) – 9.7 – ((1.01 * 13 * 0.85)/(0.82 * 7499 * 24))

Rf = 10.67, or about 1.75 inches thickness of the spray foam insulation.

So, for the same payback period as with the fiberglass insulation, we’d actually be downgrading from R-13 to R-10.67 with the spray foam. If we wanted to increase to the equivalent R-value, our payback period with the spray foam would be nearly twice as long!

But then what’s all the fuss about spray foam insulation? Why would anyone use it if the return on investment is apparently so low? Well, the R-value of the insulation isn’t telling you the whole story here. Remember the walls of your house are not just made out of batts of insulation. There is also the framing, the siding, the sheet rock, and all the other layers to consider. And those layers typically have small cracks and crevices where the heat can leak quite easily. One of the benefits of the spray foam insulation is that it fills in and seals all those leaky spots. So not only do you have the impact of the insulation layer, but you’ve increased the insulation abilities of all those other layers as well. Insulation can be one of those things were whole is greater than the sum of the parts.

Onward, Energy Efficiency Warriors. Next time we visit this topic we’ll get to the big finale: Can you insulate a house enough such that you don’t need a furnace???

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More on Choosing Paint

A couple weeks ago I went through a run down of how to choose and environmentally friendly paint. Now I want to share a bit about what decision we made and how it is working out so far.

For some reason, the small town we bought our house in has about 50 different privately owned auto shop, but the only hardware store in town is a giant Menards. And this Menards carries 2 brands of paint – Dutch Boy and Pittsburgh Paint.

Pittsburgh Paint makes a Low-VOC paint line called “Grand Distinction”. And while the info online says it “contains considerably less VOCs than other leading paints with similar attributes,” they do not seem to actually publish the VOC levels on their website. It probably does say on the can, but *spoiler alert* this was not the paint I chose, so I don’t have the can around to check the levels.

Dutch Boy’s Low-VOC paint line is called “Refresh” and is Greenguard certified as being low in VOCs and low in other air polutents. The base paint contains 50 ppg VOCs. Refresh also claims to reduce household odors with “Arm and Hammer® technology”. But I’m honestly pretty skeptical about that. We’ll see.

low VOC paint

So far we’ve painted our living room and our front room with the Refresh paint, and I’ve been pretty pleased with it. There is very little odor while painting, and the little odor there is fades away very quickly – and I’ve been painting in the winter, so it’s not like I’ve got the windows open to help clear out any odors.

I’ve also been pleased with the coverage thus far. Now we’ve only gone from cream walls to white, but the ceilings took two coats of paint, and for the most part the walls only required one! We’ve got some color plans coming up, as well as painting our wooden cabinets, so I’ll report back on the coverage when I’ve seen how those projects pan out.

Choosing an Environmentally Friendly Paint

Probably one of the easiest and most affordable ways to refresh your space is to slap a coat or two of paint on the walls. However, walking into your local hardware store or big box home improvement store and coming to aisles full of paint cans can be overwhelming. I’m certainly no expert on all the types of paint and what exactly you should choose for your particular application, but I can tell you how to choose an environmentally friendly paint.

choosing an environmentally friendly paint

Oil Based vs. Latex (Water Based)

The first question to address when choosing and environmentally friendly paint is whether to go with an oil based paint or a latex paint.

Oil based paints are slower drying which can provide a smoother finish, as any pools or ridges will have a chance to settle before the paint is completely dry. Oil based paints also can have better coverage, which means fewer coats, and can hold up better over time. However, oil based paints require more harsh chemicals to keep the colors suspended in the paint. Not only do oil based paints require special disposal at a hazardous material collection center because of these harsh chemicals, but they also give off a lot of fumes. These fumes are dangerous to breathe in. Oil paints also require harsh chemical solvents for clean up.

Latex, or water based paint, dries faster, can be fairly easily cleaned with water, and resists yellowing over time (another common issue with oil based paints). Latex paint contains fewer hazardous chemicals than oil based paint, but still contains some and can release harmful fumes. Latex paint should not be dumped down the drain, or just put in the trash in its liquid state, but if it needs to be disposed of, it can be dried up by soaking it up with kitty litter, newspaper, or sawdust.

When given the option between oil or latex paint, the more environmentally friendly paint is latex paint.

Volatile Organic Compounds (VOCs)

The harmful fumes given off by paint are due to volatile organic compounds, or VOCs. VOCs are emitted gases that can cause a variety of health problems when breathed in. VOCs can be found in paints, household cleaners, adhesives, pesticides, and building materials among other things. In paint, the chemicals that make up VOCs are used to hold the dyes suspended in the paint. After the paint is spread, the VOCs evaporate out, and the color stays in the dried paint. The US government has created a standard of 250 grams per liter of VOCs for flat paints and 380 g/l for other finishes. However, California, a state that frequently enacts stricter environmental regulations, has capped VOCs at 50 g/l for all finishes. Paints that adhere to the California regulations typically label themselves as Low-VOC. (It’s important to note that in order for a paint to be labeled low VOC, it only has to contain less than the government standards. You should read the label carefully to see the reported number of VOCs each brand and finish of paint contains.)

More recently some paint brands have advertised certain paint lines as being no VOC. In order to do so, they must contain less than 5 g/l of VOCs. Some paint brands have also opted to get evaluated by third party certification programs such as Greenguard or Green Seal to set themselves apart as environmentally friendly paint choices. These certifications evaluate the paint on more than just VOC levels as well and award their labels to paints that meet their environmental standards.

To choose a more environmentally friendly paint, look for low- or no VOC paint options, or paints that have received Greenguard or Green Seal certification.

 Natural Paints

There are some paint options that do not contain the harsh solvents used in oil or latex paints. These paints are instead pigmented with naturally occurring materials such as clay, lime, linseed oil, or chalk. Natural paints do not contain VOCs, but they do come with drawbacks. The color choices are limited, drying time can be long, coverage can be not great, and they are typically significantly more expensive than latex paint. You can find information on making your own natural paint and a list of natural paints here.

If you want to make the most environmentally friendly paint choice, and your needs can be met by the limitations above, look for natural paints.

 

Related: Tell Me More About Greenguard Certification

Happy 2015

Happy 2015Happy 2015!

How’s it feeling now that you’ve had a week to break it in?

Let’s start this year off with a bang: We bought a house!  Due to job related circumstances we will only be living in the house part time between now and June, and we will spend the rest of our time in our current apartment. This will provide us with plenty of time to get some updates and projects done before we move in for good this summer.

Now you might be wondering, what does this house have to do with this little blog? Well, it means that as we do house renovation projects, I’ll have plenty of opportunity to share with you all of those green building home renovation projects, like:

  • What are the most earth friendly paints, stains, and adhesives to use?
  • Which are the most sustainable flooring materials?
  • How do you go from lawn to organic garden (hopefully without your neighbors giving you the side-eye)?

Another blog series that I have in the works is on making a house more energy efficient. I’ll take a look at the energy usage of this house, and similar sized houses in the neighborhood, and do monthly updates on what we have done to bring that energy use down.

Aside from the house, in 2015 I’ll be continuing the series on “green” certifications in the construction and home furnishing areas. I’ll also continue to explore passive house design, integrative design, green living habits, and compost.

If there is anything you’d like to see in the upcoming year, be sure to leave a comment or drop me email.

I know I’m excited for everything that 2015 has to bring! I hope your new year is starting out shiny and bright and not too cold!

Adding Insulation for Energy Efficiency Part 1

adding insulation for energy efficiency

Untitled” by Jesus Rodriguez // CC BY

As we continue to explore the possibility of building a house that doesn’t require a heating and cooling system, the next step is to get to know the current standard for adding insulation for energy efficiency. This is a topic that involves a bit of math. In this post, I’ll walk you through the equations that are used to determine how much insulation to add. In the next post on insulation I’ll go through two simple examples of working out how much insulation to add.

Payback Period

The typical plan for adding insulation for energy efficiency is to add to the point where you are able to cover the costs of the added material with the money that you will be saving in heating and cooling costs. The time it takes to recoup the money for energy efficiency upgrades is called the payback period. For the insulation of a residential building the average payback period that most people are interested in waiting is between 4 and 5 years. So, in order to figure out the payback period we need to consider the R-value of the insulation, and the cost of heating and cooling the house per year.

Calculating the R-Value

As you may remember from my last post on insulation, the R-Value is a numerical value given to insulation that tells you how much the insulation is going to resist the flow of heat. Determining the R-Value of an insulation material depends on a number of different factors:

  • Initial indoor temperature (Ti)
  • Outdoor temperature (To)
  • time (t)
  • surface area of the building (A)
  • The heat loss indoors (dQ)

And the equation looks like this:

R = (Ti – To) * A *t / dQ

The good news about R-Value calculations is that you usually don’t have to do them. Since the measurements to complete the calculation are done in a lab setting in a controlled environment, the insulation manufacturer provides that information for you when you choose your material.

Calculating the Payback Period

In order to calculate the payback period of adding insulation, we need to take into account the insulation and the heat system.  The payback period depends on the following features:

  • R-value of the initial insulation (Ri)
  • R-value of the final insulation (Rf)
  • Cost of insulation (Ci)
  • Efficiency of the heat system (E)
  • Cost of energy (Ce)
  • Number of days that require heat per year (t)

And the equation looks like this:

P = (Ci * Ri * Rf * E) / (Ce * (R2 – R1) * t)

You can find more information on calculating the payback period of adding insulation here.

I know looking at all these equations can be intimidating if you are interested in figuring out how much insulation to add to your house to meet the 4 – 5 year payback period. But hopefully after I work through a couple examples in my next post on insulation, it will seem manageable. Maybe you’ll even be inspired to add insulation to your own house to make it more energy efficient.