Most efficient way to heat????

[williaty]

That's faulty thinking and the data points on that graph are faulty. Show me how the values on that graph are determined.

The graph is produced from the equation that defines R-Value.

An R value of 1 does not by definition decrease the heat flow by a percentage and especially not by a fixed 50 %.  Every unit of resistance to heat flow acts the same in a given situation. It's the same as the flow of water in a pipe. Every unit of resistance contributes equally to the total resistance. It's a totally linear relationship and your chart is not linear.

You're right, I made a typo. It's R2 that blocks 50% of the energy flow. Beyond that, you have no idea what you're talking about. The definition of R value is the inverse of U-value (1/U). U-value is the fraction of thermal power that passes through a given insulator under test. So a U-value of 0.5 means 50% transmission of the thermal power under test conditions. The inverse of 0.5 is 2, so a R2 insulator results in a 50% blockage of thermal power.

The improvement of a 1 R-value (or 10 R-value or whatever you feel like using) decreases as you increase the total R-value of the assembly. Look at it this way: Going from 90% blockage (10% loss) to 95% blockage (5% loss) did cut your thermal loss in half which is why you think it's linear. However, you only saved 5% of your total heating load, which isn't significant. That's how the returns diminish.

[Gary_C]

The graph is produced from the equation that defines R-Value.

Beyond that, you have no idea what you're talking about.

So show us the equation so we can see who doesn't know what they are talking about.

The relationship between heat flow and thermal resistance even if you use the U-value which is only related to R-value is still a linear or first order equation and what you are showing in your graph is definitely not linear. You could allow it to be non linear as it is if you allow the Delta T to change but that is would make it an inaccurate graph which it is.

[Holmes]

 I believe williaty's graph shows exactly what he is talking about. You can go only so far then the application of insulation is not a beneficial expense.

[Gary_C]

  You can go only so far then the application of insulation is not a beneficial expense.

There is no argument about that general statement.

But that is a financial claim while the graph compares heat flow vs. R-value and is inaccurate because there is a linear relationship between the two values. Just look at the x and y values and they have nothing to do with finances.

[williaty]

So show us the equation so we can see who doesn't know what they are talking about.

Look it up. It's not like building science is hidden from you just because you don't have a PhD.

The relationship between heat flow and thermal resistance even if you use the U-value which is only related to R-value is still a linear or first order equation and what you are showing in your graph is definitely not linear. You could allow it to be non linear as it is if you allow the Delta T to change but that is would make it an inaccurate graph which it is.

The Delta-T is not changing. Look, go read anything about this written by Martin Holiday, Alison Bailes, or Joe Listebrik (who's name I never spell correctly). They're the world's foremost experts on building science. In fact, that graph came from one of their lecture series.

What you can't get your head around is that you have to use twice as much insulation to cut the remaining heat loss in half. That results in a 1 R-value increment being an ever-smaller thermal difference which is what that graph shows. As you increase the R-value of the insulation, the heat transmittance asymptotically approaches zero, it doesn't linearly descend to zero.

[John Mc]

the r-value per inch of spray foam is 6.5 per inch; fiberglass and cellulose is around 3.5 per inch. Foam is a complete air seal so its a lot easier to heat.  But it's more about heat loss than r-value with spray foam. 
4" of foam stops 96% of heat loss;
5" stops 98% of heat loss
6" stops 98.5% of heat loss. 

His feeling was that anything after 4 to 5" of foam you are kind of throwing your money away (we had to do more than that to meet code, but code does not really take into account the difference between foam and fiberglass bats as far as overall heat loss is concerned). You're better off putting your money into a better heating system, passive solar design, thermal mass considerations (so you can make the best use of your heating system), or possibly solar PV (around here, electric rates are high enough that it makes a lot of sense)

Sorry but that claim makes no sense. R-value is a measure of resistance to heat transfer and is linear, ie if you double the resistance you will halve the heat transferred. There is no law of diminishing returns from more resistance.

What you have described is a decidedly non-linear function. In fact, it's a 1/X function. Yes, doubling R-value does cut heat transfer in half, but doubling it again doesn't cut out the other half (taking it to zero) it cuts out half of the remaining heat transfer (or 1/4 of the original heat loss).

I've attached a graph showing the function you describe. It assumes the heat transfer of an R-value of 1 = 100 (this allows the rest of the heat transfer data points to be viewed as a percent of R-1). By your description, doubling to R-2 would halve the heat transfer of 50. Doubling again to R-4 would halve it again to 25. I took this up to R-32 in the graph. The graph shows it much better than words, but you can clearly see the diminishing returns. Going from R-1 to R2 cuts heat transfer by 50. Going from R-31 to R-32 cuts the heat transfer by 0.1

[Gary_C]

Look guys, this is a pointless discussion and few people care. I have repeatedly accepted the idea there is an economic disadvantage to adding more insulation. The problem is the original chart is not scientifically accurate and as I see now it's really not intended to be anything more than an illustration of the concept. I now see the illustration maker covered this discrepancy by stating the points were stepwise points and though it was not noted, those points are at different conditions. If you are going to look at individual layers of insulation you technically should look at the delta T across those individual layers and note those delta T's are changing, not the R-value.   

What you have described is a decidedly non-linear function. In fact, it's a 1/X function. Yes, doubling R-value does cut heat transfer in half, but doubling it again doesn't cut out the other half (taking it to zero) it cuts out half of the remaining heat transfer (or 1/4 of the original heat loss).

It makes no difference if its X or it's reciprocal 1/X it's still a linear function of X. In order for it to be non-linear function, it would have to be X² or 1/X² or higher order equation. That's why there is no formula or equation to describe the illustration. It's a bunch of steps at different conditions which defies a single formula.

Enough said.

[Hilltop366]

So moving on, the most efficient way to heat is to not have to heat a lot. ;D

Once you know your heating requirements it will be easier to figure out the best solution(s).

Did anyone see the article about how fibreglass batts lose there insulating effectiveness at colder temperatures, as I understand it the air inside the wall cavity (even if there is no air leaks) will circulate in the wall cavity as it cools reducing the insulating effectiveness. The colder it gets the (when you need it the most) the less it works!

[wndwlkr65]

the most efficient way to heat my house is with the most efficient wood stove on the planet. Ideal steel. It's simply amazing.

[reprod]

Great thread!!!
I have been studying this for the past few days and gotten the same information every where I have looked.
I am also building a new house this spring.
Although I hadn't planned it, we are going to get the benefit of passive solar.
I am intrigued by the hrv/erv systems.  I need to learn more about this. 
We have a mild climate where I live.  It seldom gets down to 20 deg or above 90 deg F. 
I have been thinking about installing radiant heat in the basement slab and was wondering if anyone has information about incorporating the radiant heat design with their traditional wood stove.

[Qweaver]

Here is what made up my mind.  My Geothermal system cost less than $20,000 and then gave me a $6000 tax rebate.  That's for equipment, duct work and labor. An electric system would have been the same with no rebate.  Our highest electric bill, heating or cooling, has been $150 and averages @ $100---for an all electric 2400 SqFt house.   Plus we like moving conditioned air.  We have five over head fans that turn constantly.  7 if you count the porch.

[LittleJohn]

Great thread!!!
I have been studying this for the past few days and gotten the same information every where I have looked.
I am also building a new house this spring.
Although I hadn't planned it, we are going to get the benefit of passive solar.
I am intrigued by the hrv/erv systems.  I need to learn more about this. 
We have a mild climate where I live.  It seldom gets down to 20 deg or above 90 deg F. 
I have been thinking about installing radiant heat in the basement slab and was wondering if anyone has information about incorporating the radiant heat design with their traditional wood stove.

It can be done, the biggest concerns that I would have, is that you can not have water that exceed 130F enter your slab, so you will need some mechanism (mixing valve or other plumbing design) to control that; but most OWB do not water temperature below 140f (condensation issues in firebox).  Trust me it can be done, cause I have HEATED floors in my basement  ;)

[John Mc]

Great thread!!!
I have been studying this for the past few days and gotten the same information every where I have looked.
I am also building a new house this spring.
Although I hadn't planned it, we are going to get the benefit of passive solar.
I am intrigued by the hrv/erv systems.  I need to learn more about this. 
We have a mild climate where I live.  It seldom gets down to 20 deg or above 90 deg F. 
I have been thinking about installing radiant heat in the basement slab and was wondering if anyone has information about incorporating the radiant heat design with their traditional wood stove.

It can be done, the biggest concerns that I would have, is that you can not have water that exceed 130F enter your slab, so you will need some mechanism (mixing valve or other plumbing design) to control that; but most OWB do not water temperature below 140f (condensation issues in firebox).  Trust me it can be done, cause I have HEATED floors in my basement  ;)

ANY well designed radiant floor heat will have a mixing valve to control the temperature - probably one for each zone.

[Al_Smith]

I have a "water furnace" geo-thermal .It's supposed to be the most efficient method to heat and cool but it certainly is not free .Then again say what you will wood heat is not truly free either if you figure your time and the work involved in it . It's been said there is no free wood pile .

[williaty]

I have a Waterfurnace geothermal system as well. The previous owners installed so at least I didn't have to pay for the heap of junk. The huge extra initial cost of a geothermal system is supposed to be made up by energy savings over the coming decades. In a factory designed test lab install, I'm sure that's true. In the real world, there are so many hundreds of tiny details that each can keep the system from achieving its advertised efficiency that I bet only 1 or 2 owners in 100 ever break even (let alone turn a profit!) before the furnace has to be replaced (at a huge additional cost compared to a conventional furnace). On top of that, it's miserable to live with and the service on it costs considerably more because most of the HVAC companies around here won't touch it so you have to use a geothermal specialist and the Waterfurnace brand takes off-sized filters that you pay a premium for.

Geothermal has to be one of the biggest scams ever perpetrated against the American public at home and garden shows!

The poor performance and high cost from our Waterfurnace is actually how we ended up with a wood stove. We're actually comfortable for the first time since buying the house this winter, the house stays at temperature even when below 0F (the Waterfurnace couldn't keep up) and, even counting the time we work harvesting firewood at the same dollar value per hour that we'd make at work, it's cheaper than the geo.

[John Mc]

... even counting the time we work harvesting firewood at the same dollar value per hour that we'd make at work, it's cheaper than the geo.

Wow! either that furnace or installation must really stink, or you are a whole lot more efficient with your firewood harvesting than I am (or maybe both?)

I have no personal experience with geothermal, but a few friends had it when I lived in Ohio, and they loved it (and had cheap heating bills).

[williaty]

Actually, I'm giving the Waterfurnace the benefit of the doubt and pretending it really is the 300% efficient that the manufacturer claims in making that comparison. In reality, we'd be lucky to be hitting 100-110% total system efficiency (because you HAVE to include the pump in the cost of heating!) on the geo. Our best estimate is that a cord felled, bucked, split, and stacked has an aggregate cost of ~$85-$90. At that, comparing the geo at 300% efficient to the wood stove at 82% efficient, per BTU it costs about half as much to heat with the wood as it does to run the Waterfurnace. If you take a more realistic assumption of 150% efficiency for the Waterfurnace, the wood costs about 75% less. Once we've caught up on the years of neglect to our woods and have to start buying cordwood to have enough for the winter, the economics will change. It'll cost about the same to buy split cordwood as it would to run the Waterfurnace at 300% fairytale efficiency. In the real world, at 150% efficiency, it'll cost about half as much to heat with bought split cordwood as it will to run the Waterfurnace.

If you figure in your soup to nuts cost on the Waterfurnace and every energy and dollar input to it, about the only heating method worse than it is electric resistance heat. The days where there was any argument for the fake geothermal heat we use in the USA (which is really more accurately called a ground-sourced heat pump) are gone. The new mini-split air-sourced heat pumps with variable refrigerant flow are so freaking efficient now and cost so, so much less than a geo install that they rule the roost in most cases. About the only place they don't work well is in climate zones where it gets seriously cold and stays that way in the winter. But hey, that just means you need a wood stove to do the heavy lifting!

[Al_Smith]

Depends on one perspective I suppose .In my case in the middle of a giant midwestern corn field just to get natural gas to my property it would cost over 7000 dollars .

Propane unless you own the tank is a legal piracy,I've dealt with those people before .So what's left,electric heat in some form .

I already had radiant heat in the ceiling which works well but is expensive.An air to air heat pump doesn't work very well in colder temps,geo was the only choice left which does work well .I've had two,the first one was a used unit that cost me 800 bucks and I got 9 years out of it before the heat exchanger went bad.

The replacement was 3400,bought at wholesale price .Due to my failure to make sure the air filters were clear I cooked the compressor which cost me a grand to replace after 8 years .Now keep in mind I understand refridgeration and heating and all work installation ,maintainence  is all done by me so there are no labor costs .

I might add as I type this post I am sitting in a room at about 75 degrees from the heat of a wood burner and outside I have 9 cords of hardwood split and stacked .

Problem is when I'm not at home it won't stoke itself .So geo is an option .Perhaps not for someone who doesn't understand how it works or has to rely on others to do work on same though .BTW the average life of a unit is about 20 years .In that 20 years it will pay for it's self ,how much I have no idea but all things considered I would not classify the system as "junk",more so misunderstood .

[woodshax]

Although the R value topic has been beaten to death....I used to own a spray foam company (sold in 2013) and did a lot of spraying...I love the product...hate the business model.   So...in the real world R- value sucks....it is an equation that only holds up in the lab...with a heat lamp underneath a piece of insulation measuring the heat change over time.....it does not account for voids, the convective effect in walls that degrades performance as pointed out.   So I told people any more than 3 1/2 inches of closed cell was a waste off money and unless they were looking to make a safe room for bad storms .....up north closed cell foam is the way to go and at 2" or more it is a vapor and moisture barrier and provides a lot of structural strength to the home. Although code will give a minimum R-value, many area inspectors waive that for spray foam because 6 inches of open cell foam ( in texas most roofs use 2x6s so 6 inches covers the studs and stops heat transference) sprayed on the underside of the roof deck (turning it into a closed system...no gable or soffet venting) which depending on the foam maker is about R-20 performs much better than R-30 blown in on the attic floor and everything is better than batting....just remember by code you can't leave spray foam "wild" (uncovered by sheetrock or paneling or metal) unless in an attic with no storage unless you apply a very expensive 30 minute fire barrier like DC 315..... I ain't so smart on science but before I started selling foam I made sure I understood the pros and cons....As a retired Army LTC i figure I had enough active brain cells to get most of it right so I could better explain it to home owners and allow them to make an informed choice