Oil to Propane Heating Conversion - worth it?

[TRC]

Has anyone done an Oil to Propane Heating Conversion in their house? My heating guy is suggesting we think about it. Our oil heating system works, but it's about 12 years old and was a "builder's grade" system (uses forced hot air). Efficiency is about 82%. Our hot water tank is also one of those deals where our furnace constantly heats the water, then it cools, then it heats it again - regardless of if we use it. He said the "tankless water heaters" are the way to go, as it's on demand heated water, only when you need it.

From what I gather, Propane Heating systems burn at a much higher efficiency, and the cost of propane compared to oil is cheaper (about $1.00 cheaper per gallon where I live).

Is the ROI compelling to switch?

[hicabob]

Heating oil has a lot more energy per gallon that propane (3 gallons propane = 2 gallons fuel oil) so comparing gallon prices is not valid. I have propane - $2.60 or so/gallon delivered here (and that's a lot less than last year) - not inexpensive. I have heard that tankless water heaters are much better for the purveyor than the customer.

[THY4373]

As referenced above you need to account for the relative energy usually measured by BTU for heating contained in each unit of the fuels you are comparing. You also need to account for the efficiency of the furnaces you are comparing. Each year I compare the cost of heating via heat pump (electricity) vs. natural gas because my downstairs HVAC system can provide heat both ways. I can choose which way I want to heat to some extent by altering the external temperature cut over to natural gas or by locking out the heat pump and running 100% gas. Despite the common conviction that gas is always cheaper than electric heat (usually no distinction is made between resistance heat and heat pump), I find that my heat pump is often cheaper than natural gas. In fact during the gas price peak some years ago resistance heat would have been on par with natural gas at my location. This year I am running mostly on natural gas thanks to the great drop in prices. This is all a long winded way of saying you have to do the math for your specific situation as rules of thumb may or may not apply to you.

[FNK]

As others stated, propane is not cheaper than oil energy-wise. If you have a separate hot water storage tank, and it's well insulated, it's not significantly worse than an on-demand heater, and much more reliable.

If you have a bit of cash, consider installing a geothermal heat pump. It's cheaper than oil to run, and also optimizes cooling. There's a 30% tax break on system costs. Installation is pricy though.

[MathWizard]

Propane is quite expensive. With Natutral Gas it would be a no-brainer.

Take a look at an air source heat pump. They have relatively high efficiency down to 20 to 30 deg F.
You sould set the thermostat on your oil furnace a little below that for the heat pump so that it
would kick in whe the heat pump cannot keep up.

The heat pump can also provide cooling in the summer, and high efficiency water heating when the
temp is above 20 deg.

[TRC]

Thansk for the feedback everyone. Looks like the cost savings aren't all that compelling to switch to propane. I guess the old addage of "if it aint broke, don't fix it" applies here

[Valuethinker]

Despite the common conviction that gas is always cheaper than electric heat (usually no distinction is made between resistance heat and heat pump), I find that my heat pump is often cheaper than natural gas. .

Being pedantic (I suspect you know this but not everyone does, perhaps) it depends on the Coefficient of Performance of the Heat Pump.

At 3.0, say, you are burning 1 kwhr electricity to move 3kwhr of heat. So 3x as efficient as electric bar heating which has a COP of 1.0 (by definition), and roughly 3/ 0.9 times as efficient as a modern gas furnace with 90% efficiency.

At which point, if your gas is 4 cents/ kwhr (sorry we use kwhr not BTU, but there is a conversion formula
http://www.hamiltonit.co.uk/Tools/BTU_K ... ertor.aspx)

then it's only cheaper to burn gas if electricity is 12 cents a kwhr or more. My (UK) retail price of gas is c. 4.5p/ kwhr (so say 6.5 cents) yours is probably about half that (or less). My electricity price is c. 13-14p ie c 22 cents/ kwhr. But (see below) a kwhr of electricity is 0.6 kg of CO2. The same in gas terms in my furnace is c. 0.22 kg.

You can see why this works if you think that the average coal fired power station has efficiency of 35-40% (energy value to useful electricity), and you lose another 7-8% in distribution of electricity. A modern gas fired station is c. 55% (running on combined cycle). A gas furnace has 90% efficiency. Somehow your electricity bill has to pay for all that lost energy.

At the UK current grid intensity, heat pumps only pay if you can get COP of 4.0+. Which really means you need a ground source heat pump. If you have access to gas in the UK, then it's the way to go both for cost and environmental reasons. US that would also be true in most jurisdictions, I think.

COPs fall with outside temperature (strictly: the gap between inside and outside temperature). Somewhere around 20 degrees F I think they actually drop to 1.0 (ie electric bar heating).

If you are interested, gas in a 90% furnace efficiency generates about 220kg CO2/ 1000kwhr. Electricity it entirely depends: hydro, nuclear, wind - 0 (of course), coal 1000 kg/kwhr, gas (combined cycle gas turbine) c 540kg/ 1000kwhr. So it depends on *where* you are in the US-- how your electricity is generated. Confusingly, the *marginal* change in electricity consumption (say you turn on your heat pump at 4.30 pm on a summer or winter afternoon) has a different impact than the *average* because marginal 'peaking' plant is usually gas (so in a mid western or southern utility primarily burning coal, that would be a *drop* in intensity, in a coastal utility burning nuclear, gas etc. it might be an increase). UK average is about 0.55 kg/ kwhr (550kg per 1000 kwhr), US is closer to 0.8 (ie 800) *but* has huge regional variations (in the Pacific NW close to zero).

[Valuethinker]

Thansk for the feedback everyone. Looks like the cost savings aren't all that compelling to switch to propane. I guess the old addage of "if it aint broke, don't fix it" applies here

I am not an expert on propane pricing but I believe it tends to track the oil price more than the gas price. It's natural gas that is now in oversupply in North America, and it is unlikely that will be corrected swiftly.. ie price may get back up to $5-6/ mcf but not back to $10, in the next few years. Because shale gas often comes with tight oil, and oil is such a highly priced commodity per unit energy, companies will keep producing shale gas to get at the tight oil.

It could pay to switch to a heat pump.

With an Air Source Heat Pump if your temperatures are in the low 20s F or below frequently, then it probably would not-- basically your efficiency drops to electric bar.

What your guy tells you about hot water heating and tanks is on the level- -it's also possible to get a heat pump hot water heater (ie electric) which is very efficient.

However hot water is normally about 3500 kwhr pa for a house with 2 people. That's probably less than 1/5th of your total heating and hot water consumption.

[Valuethinker]

Has anyone done an Oil to Propane Heating Conversion in their house? My heating guy is suggesting we think about it. Our oil heating system works, but it's about 12 years old and was a "builder's grade" system (uses forced hot air). Efficiency is about 82%. Our hot water tank is also one of those deals where our furnace constantly heats the water, then it cools, then it heats it again - regardless of if we use it. He said the "tankless water heaters" are the way to go, as it's on demand heated water, only when you need it.

Looking at that arrangement, you may want to investigate wrapping a thermal blanket around the hot water tank. If the system is only 12 years old and well specced then that may not be necessary. We replaced our water tank with an 'eco' one (UK heating systems use an 'indirect' system, where the furnace heats both the hot water and the rads (forced air is rare/ unknown)) which has 6' factory sprayed on foam and the heat loss is minimal.

Just by wrapping a blanket you could save 5% of energy use (to heat hot water). Also insulating the pipes around the thing (easy to do, the sleaves come pre made).

On tankless we were advised (correctly I think) that they are OK for a couple but don't work well if you have a family or frequent guests. Because your hot water output at any moment is exactly limited to what the burner puts out.

Note that the 'waste' heat out of the tank goes into the house (at least partially, less so if in a cold basement) so it offsets (somewhat) your actual direct heating bill (in winter).

[FNK]

Looks like I've found a fellow electricity geek.

[THY4373]

Despite the common conviction that gas is always cheaper than electric heat (usually no distinction is made between resistance heat and heat pump), I find that my heat pump is often cheaper than natural gas. .

Being pedantic (I suspect you know this but not everyone does, perhaps) it depends on the Coefficient of Performance of the Heat Pump.

Yes I have the COP chart for my unit and to keep things simple I choose 40 degrees F as my point of comparison (which is the avg. temp in January). I set the thermostat to cut over to fossil at 35 degrees F or higher external temperature depending on relative gas/electric rates so I never run the heat pump below 35 degrees F (it might actually still be cost effective to go lower but at around 30 degrees it reaches a balance point where it can only just keep up with heat losses and I don't have the option with my setup to run gas and heat pump at the same time). I don't have the figures in front of me (travelling) but our marginal electric rates drop massively in the winter here while the gas rates go up. As point of reference my marginal electric rate in the winter including a green energy rider of 1 cent I volunteer for is about 7 cents so basically 1/3 your rate. My gas rate is around $1.10 a therm this winter. These both include the distribution costs billed per unit of energy consumed which in the case of gas is more than 50% of the overall price for a therm. This does not include any fixed fees I pay to just have service.

Correct my math if I am wrong:

Gas cost per KWH of energy:
1 Therm = 29.3 KWH * .80 (efficiency of my furnace) = 23.44 KHW
1.10/ therm / 23.44 = $.047

Electric cost via Heat Pump per KWH:
1 KWH * 2.5 (COP) = 2.5 KWH
.07/KWH / 2.5 = $.028

Edit: I should add that if you looked at my average rate for the whole year it is closer to 11 cents/KWH and the math would look a lot different especially since gas drops quite a bit in summer here. But I don't run the heat in the summer.

[FNK]

But (see below) a kwhr of electricity is 0.6 kg of CO2. The same in gas terms in my furnace is c. 0.22 kg.

Oh, by the way, once you factor in the COP, a kWh of electric heat pump heat is 0.6/3=0.2, on par with gas.

Generally, if you're paying less for something ultimately fuel-based, you're probably using less fuel.

[Valuethinker]

But (see below) a kwhr of electricity is 0.6 kg of CO2. The same in gas terms in my furnace is c. 0.22 kg.

Oh, by the way, once you factor in the COP, a kWh of electric heat pump heat is 0.6/3=0.2, on par with gas.

Generally, if you're paying less for something ultimately fuel-based, you're probably using less fuel.

I agree in that I was trying to find the breakeven point-- which is somewhere around 3.5 times here. A study by the Energy Saving Trust of heat pumps (GSHP) showed huge variations in COP related to bad installation or incorrect operation. From like 1.0 to 5.0 range. It's not a technology that has been mastered here. ASHP are probably just as rare.

On that latter point I am not sure that is true. In that coal is so cheap (compared to natural gas about half the cost per unit energy) and oil so expensive (about 4-5 times natural gas at North American prices, I believe).

Energy differs hugely in price depending on form of delivery.

The numbers below show that per unit energy electricity is about 3 times natural gas, oil about 60% more than natural gas, coal about 40% more (these are retail prices).

Roughly speaking here, one is paying 60p a litre (say $3.80/ US gallon) for oil, as below. That should be close to the US level, as there is no vehicle fuel duty on home heating oil (gasoline would be over $8/ gallon, they are quite brutal about marking and checking 'red' diesel to make sure it is used in agricultural machinery, not cars). There is 5% VAT (not in these numbers).

http://www.nottenergy.com/energy_cost_comparison/

Fuel Pence per kWh (after boiler efficiency) CO2e emissions per kWh*
Electricity Standard Rate1 15.53 0.590
Electricity Online Rate1 14.72 0.590
Mains Gas Standard Rate2 5.24 0.227

Below I have included the price per unit as well so the comparison is the latter 2 numbers with the above. It's clearer on the actual chart cited if you click through.

Kerosene3 63.40 Litre 7.19 (90%) 0.314
Gas oil4 76.77 Litre 8.20 (90%) 0.352
LPG5 51.08 Litre 8.52 (90%) 0.259
Butane6 136.96 Litre 19.09 (90%) 0.259
Propane7 72.33 Litre 11.37 (90%) 0.259
Seasoned Wood8 21.89 Kg 6.13 (85%) 0.025
Pellets9 27.84 Kg 6.69 (90%) 0.039
Smokeless fuel10 43.31 Kg 8.62 (75%) 0.414
Coal10 33.63 Kg 6.55 (75%) 0.414
GSHP11 14.72 kWh 4.21 (350%) 0.184
ASHP11 14.72 kWh 5.45 (270%) 0.236


So COP GSHP 3.5x, ASHP 2.7x assumed.

('Green' energy tariffs here are anything but (with the small exceptions of a handfull of pure wind farm operators who reinvest the fees in new wind and solar ventures). Basically they simply mean the utility has bought a 'Renewable Obligation Certificate' to offset your purchase of electricity. It is 'greenwash'-- the only real 'green' saving is not to use the energy in the first place.)

[Valuethinker]

Despite the common conviction that gas is always cheaper than electric heat (usually no distinction is made between resistance heat and heat pump), I find that my heat pump is often cheaper than natural gas. .

Being pedantic (I suspect you know this but not everyone does, perhaps) it depends on the Coefficient of Performance of the Heat Pump.

Yes I have the COP chart for my unit and to keep things simple I choose 40 degrees F as my point of comparison (which is the avg. temp in January). I set the thermostat to cut over to fossil at 35 degrees F or higher external temperature depending on relative gas/electric rates so I never run the heat pump below 35 degrees F (it might actually still be cost effective to go lower but at around 30 degrees it reaches a balance point where it can only just keep up with heat losses and I don't have the option with my setup to run gas and heat pump at the same time). I don't have the figures in front of me (travelling) but our marginal electric rates drop massively in the winter here while the gas rates go up. As point of reference my marginal electric rate in the winter including a green energy rider of 1 cent I volunteer for is about 7 cents so basically 1/3 your rate. My gas rate is around $1.10 a therm this winter. These both include the distribution costs billed per unit of energy consumed which in the case of gas is more than 50% of the overall price for a therm. This does not include any fixed fees I pay to just have service.

Correct my math if I am wrong:

Gas cost per KWH of energy:
1 Therm = 29.3 KWH * .80 (efficiency of my furnace) = 23.44 KHW
1.10/ therm / 23.44 = $.047

Electric cost via Heat Pump per KWH:
1 KWH * 2.5 (COP) = 2.5 KWH
.07/KWH / 2.5 = $.028

Edit: I should add that if you looked at my average rate for the whole year it is closer to 11 cents/KWH and the math would look a lot different especially since gas drops quite a bit in summer here. But I don't run the heat in the summer.

With that high a winter temp, I am guessing you live in the South East? UK still has a January peak demand for electricity (interestingly, Ontario has swapped over to a summer peak demand-- increased use of air conditioning, the urban heat island effect and warmer summers) as residential air con is still almost unknown (for how much longer?). We do not (yet) have seasonal electricity rates.

You are probably wise not to run gas and HP at the same time-- the control systems would just get confused and do bad or expensive things.

I'd have to check your math re therms but it looks about right-- your retail gas price is somewhat higher than I would have expected (I think my relatives in Ontario pay about half what I do in the UK).

[THY4373]

With that high a winter temp, I am guessing you live in the South East? UK still has a January peak demand for electricity (interestingly, Ontario has swapped over to a summer peak demand-- increased use of air conditioning, the urban heat island effect and warmer summers) as residential air con is still almost unknown (for how much longer?). We do not (yet) have seasonal electricity rates.

You are probably wise not to run gas and HP at the same time-- the control systems would just get confused and do bad or expensive things.

I'd have to check your math re therms but it looks about right-- your retail gas price is somewhat higher than I would have expected (I think my relatives in Ontario pay about half what I do in the UK).

Yeah our gas rates are higher than US average for sure and our electric rates are lower than average at least in the winter. I have family who live in another state about 90 miles away and they pay quite a bit less for gas and a bit more for electricity so the math works out quite differently. That is why I always suggest folks run the numbers for themselves as at least in the States we have quite a bit of regional variation in the rates. And yes you are correct I do live in the south east which also plays into the heat pump as well (air source ones are very common here, with newer houses having fossil backup and older ones resistance heat backup). Back when gas prices peaked around here (I think 06) I was paying around $2.00 a therm and my winter electric rates at that time were around 4 cents. At that point even resistance heat was cheaper than gas which common sense would say shouldn't happen.

[Valuethinker]

With that high a winter temp, I am guessing you live in the South East? UK still has a January peak demand for electricity (interestingly, Ontario has swapped over to a summer peak demand-- increased use of air conditioning, the urban heat island effect and warmer summers) as residential air con is still almost unknown (for how much longer?). We do not (yet) have seasonal electricity rates.

You are probably wise not to run gas and HP at the same time-- the control systems would just get confused and do bad or expensive things.

I'd have to check your math re therms but it looks about right-- your retail gas price is somewhat higher than I would have expected (I think my relatives in Ontario pay about half what I do in the UK).

Yeah our gas rates are higher than US average for sure and our electric rates are lower than average at least in the winter. I have family who live in another state about 90 miles away and they pay quite a bit less for gas and a bit more for electricity so the math works out quite differently. That is why I always suggest folks run the numbers for themselves as at least in the States we have quite a bit of regional variation in the rates. And yes you are correct I do live in the south east which also plays into the heat pump as well (air source ones are very common here, with newer houses having fossil backup and older ones resistance heat backup). Back when gas prices peaked around here (I think 06) I was paying around $2.00 a therm and my winter electric rates at that time were around 4 cents. At that point even resistance heat was cheaper than gas which common sense would say shouldn't happen.

Thank you for all that-- very interesting.

North America has relatively low utility rates which, given the harshness of the climate (residential AC is still a real rarity in Europe-- you see room air conditioners in hot countries; conversely almost any country with a harsh winter in Europe has a short and relatively mild summer (you have to get to Russia, say, to get a Chicago-style climate)) is a good thing.

Disappointing thing is howly badly built houses in much of N America are from the point of view of airtightness and insulation (British houses are generally worse, but then our average winter temp is probably in the 40s F, and summer temp in the high 60s).

[FNK]

Disappointing thing is howly badly built houses in much of N America are from the point of view of airtightness and insulation

Don't. Get. Me. Started.

78 mm of fiberglass. 78 mm!!!

[THY4373]

Disappointing thing is howly badly built houses in much of N America are from the point of view of airtightness and insulation

Don't. Get. Me. Started.

78 mm of fiberglass. 78 mm!!!

Agreed my relatively well built (it was custom built not spec house--I am the third owner) from 1986 has (or mostly had) all kinds of leaks and insulation problems I have been correcting. The one that really got me was my down draft stove top that vented through the cabinet and floor into the unconditioned crawl space. The installer in 1986 had cut a 9" square hole for a 6" round vent. I wondered the first winter why I had ice cold air blowing on my feet from under the cabinet (it is crazy to think it was that way from 1986 until 2003 when I bought the house). I fixed that real quick and I have spent quite a bit of time tightening up the house so it is much better now. Also went to R50+ in the attic.

[FNK]

Also went to R50+ in the attic.

(R50+ is 300-500 mm).

[tomd37]

THY4373,

We often wondered why the inside of one of our kitchen cabinets was always warm or cool (winter or summer). It had a toe-plate vent coming out the front. We had a HVAC friend relocate the vent to come up through the floor in front of the cabinet. Did a major renovation including replacing all the cabinetry and discovered the builder just ran the old ductwork off the supply line up under the cabinet, but did not put any duct from there to the toe-plate. Therefore the heat and air conditioning was just hitting the base of the cabinet. When I mentioned this to several neighbors who were doing similar kitchen renovations, they discovered the same situation as we had. Bet there are a lot more of similar situations in this subdivision of 162 homes all built by the same builder in the early 1990s.

[THY4373]

Also went to R50+ in the attic.

(R50+ is 300-500 mm).

Yeah I probably have something like 20-24+" of fiberglass insulation both the original blown in and fiberglass batts on tops. I wouldn't have gone so far but got a lot of R30 rolls cheap on craigslist.

[THY4373]

THY4373,

We often wondered why the inside of one of our kitchen cabinets was always warm or cool (winter or summer). It had a toe-plate vent coming out the front. We had a HVAC friend relocate the vent to come up through the floor in front of the cabinet. Did a major renovation including replacing all the cabinetry and discovered the builder just ran the old ductwork off the supply line up under the cabinet, but did not put any duct from there to the toe-plate. Therefore the heat and air conditioning was just hitting the base of the cabinet. When I mentioned this to several neighbors who were doing similar kitchen renovations, they discovered the same situation as we had. Bet there are a lot more of similar situations in this subdivision of 162 homes all built by the same builder in the early 1990s.

That is just insane it is amazing what builders will do. For my retirement house I am really tempted to have one custom built and watch them like hawks so they don't do such crazy things.

[Valuethinker]

THY4373,

We often wondered why the inside of one of our kitchen cabinets was always warm or cool (winter or summer). It had a toe-plate vent coming out the front. We had a HVAC friend relocate the vent to come up through the floor in front of the cabinet. Did a major renovation including replacing all the cabinetry and discovered the builder just ran the old ductwork off the supply line up under the cabinet, but did not put any duct from there to the toe-plate. Therefore the heat and air conditioning was just hitting the base of the cabinet. When I mentioned this to several neighbors who were doing similar kitchen renovations, they discovered the same situation as we had. Bet there are a lot more of similar situations in this subdivision of 162 homes all built by the same builder in the early 1990s.

That is just insane it is amazing what builders will do. For my retirement house I am really tempted to have one custom built and watch them like hawks so they don't do such crazy things.

Unless you get a factory built 'kit' house like the Germans and Scandinavians do, I suspect it's really hard to get this stuff right. If factory built, much more of the house in built to engineered quality and specification.

Air leakiness in particular.

Even then, you are vulnerable to bad 'finish' on the internals.

[pshonore]

Also went to R50+ in the attic.

(R50+ is 300-500 mm).

Yeah I probably have something like 20-24+" of fiberglass insulation both the original blown in and fiberglass batts on tops. I wouldn't have gone so far but got a lot of R30 rolls cheap on craigslist.

That brings up a silly question. Is there a maximum thickness of fiberglass before you get diminishing returns? Compressing fiberglass insulation reduces the R Value and is there a point when its gets compressed from the weight of layers above? Or is this not a worry?

[Valuethinker]

Also went to R50+ in the attic.

(R50+ is 300-500 mm).

Yeah I probably have something like 20-24+" of fiberglass insulation both the original blown in and fiberglass batts on tops. I wouldn't have gone so far but got a lot of R30 rolls cheap on craigslist.

That brings up a silly question.

Not a silly question. I don't think this stuff is obvious unless you have an engineering degree (and I certainly don't).

Is there a maximum thickness of fiberglass before you get diminishing returns? Compressing fiberglass insulation reduces the R Value and is there a point when its gets compressed from the weight of layers above? Or is this not a worry?

Yes there is diminishing marginal returns.

We use U values u = 1/R (but to get your R from our R, multiply by 5.6-- we use degrees C and square metres)

So u = 1.0 W/m2 K (ie watts per square metre x degrees kelvin of temperature difference)

So if R value of 100mm (4") is 2.5 then U = 0.4 (in your terms R = 14.0) - EDITED U value as per Epsilon Delta below

Double that to 8"/ 200mm, and you get R = 5.0. So U = 0.2

ie roughly speaking the doubling cuts heat loss by (0.4-0.2)/ 0.4 = -50 % for doubling 50% fewer watts lost per square metre x degree K temperature diff w outside

Go to 400mm (ie 16"), R=10 (R56 in your terms), U = 0.1 and savings is 0.4-0.1/ 0.4 = -75% for quadrupling

EDITED: as per Epsilon Delta below, double the thickness, halve the heat loss. However that means you have diminishing marginal returns.

On your second question I am not sure, but I would imagine when quoted there is a figure for compression included when R value is quoted?

Deterioration of insulation over time due to settling, compression etc. seems to be one of those 'open secrets' about insulation-- it's going on, but no one is tracking performance post installation, so it's not reflected.

Passivhaus (the gold standard) calls for U = 0.15 or below but to get the overall Passivhaus standard (which is in watts per m2 of floorspace) you'd probably need to do a lot better than that-- 0.1 or lower

http://www.passivhaushomes.co.uk/passiv ... nical.html

[Valuethinker]

THY4373,

We often wondered why the inside of one of our kitchen cabinets was always warm or cool (winter or summer). It had a toe-plate vent coming out the front. We had a HVAC friend relocate the vent to come up through the floor in front of the cabinet. Did a major renovation including replacing all the cabinetry and discovered the builder just ran the old ductwork off the supply line up under the cabinet, but did not put any duct from there to the toe-plate. Therefore the heat and air conditioning was just hitting the base of the cabinet. When I mentioned this to several neighbors who were doing similar kitchen renovations, they discovered the same situation as we had. Bet there are a lot more of similar situations in this subdivision of 162 homes all built by the same builder in the early 1990s.

That is just insane it is amazing what builders will do. For my retirement house I am really tempted to have one custom built and watch them like hawks so they don't do such crazy things.

The industry has been deskilled and the economics are for speed (after all the buyer has limited comeback post purchase). It argues for kit built houses.

[Valuethinker]

Disappointing thing is howly badly built houses in much of N America are from the point of view of airtightness and insulation

Don't. Get. Me. Started.

78 mm of fiberglass. 78 mm!!!

Until about 5 years ago that was the UK standard for roofs, and most houses probably still have that (270mm now is the standard)-- that's for the roof. Walls even less.

My relative has a Viceroy kit home on top of a hill in central Ontario (-30 C in winter with windchill) from the 1970s. Walls are R13 about (and the insulation has settled). They do, however, have a ground source heat pump for the last 20 years and that has been a great success.

[FNK]

Passivhaus (the gold standard) calls for U = 0.15 or below but to get the overall Passivhaus standard (which is in watts per m2 of floorspace) you'd probably need to do a lot better than that-- 0.1 or lower

Passivhaus also requires an absolutely airtight house, but once you get all of that together, you suddenly get ridiculously accelerating returns:

You don't need a heating system. At all. No fuel tank, no furnace. The waste heat from your appliances is enough. You probably will need cooling in US climates, but you can get away with an absolutely minimal setup.

You do need a heat-recovery ventilation system, of course, because you'll eventually suffocate in an airtight house otherwise.

The trick is that the savings on the heating system cover almost all of the extra expense on the envelope.

[Epsilon Delta]

We use U values u = 1/R (but to get your R from our R, multiply by 5.6-- we use degrees C and square metres)

So u = 1.0 W/m2 K (ie watts per square metre x degrees kelvin of temperature difference)

So if R value of 100mm (4") is 2.5 then U = 0.25 (in your terms R = 14.0)

Double that to 8"/ 200mm, and you get R = 5.0. So U = 0.2

ie roughly speaking the doubling cuts heat loss by (0.25-0.2)/ 0.25 = -20 % for doubling 20% fewer watts lost per square metre x degree K temperature diff w outside

Ahem. 1 / 2.5 = 0.4 not 0.2

In the simple flat surface model doubling the thickness always halves heat loss. Of course the second doubling requires twice as much insulation, and saves half as much energy so you rapidly reach a point where it's cheaper to buy energy than insulation.

As an aside, if you use enough insulation the flat surface model no longer applies and you need to use the model of a spherical shell. Doubling spherical shell does not halve heat loss.

[Valuethinker]

We use U values u = 1/R (but to get your R from our R, multiply by 5.6-- we use degrees C and square metres)

So u = 1.0 W/m2 K (ie watts per square metre x degrees kelvin of temperature difference)

So if R value of 100mm (4") is 2.5 then U = 0.25 (in your terms R = 14.0)

Double that to 8"/ 200mm, and you get R = 5.0. So U = 0.2

ie roughly speaking the doubling cuts heat loss by (0.25-0.2)/ 0.25 = -20 % for doubling 20% fewer watts lost per square metre x degree K temperature diff w outside

Ahem. 1 / 2.5 = 0.4 not 0.2

In the simple flat surface model doubling the thickness always halves heat loss. Of course the second doubling requires twice as much insulation, and saves half as much energy so you rapidly reach a point where it's cheaper to buy energy than insulation.

As an aside, if you use enough insulation the flat surface model no longer applies and you need to use the model of a spherical shell. Doubling spherical shell does not halve heat loss.

Thank you. Fixed.

[FNK]

As an aside, if you use enough insulation the flat surface model no longer applies and you need to use the model of a spherical shell. Doubling spherical shell does not halve heat loss.

If you use enough insulation it will start generating heat through thermonuclear synthesis.

[Valuethinker]

Looks like I've found a fellow electricity geek.

Grew up with it. Dad built nuclear power stations. Miss his insights, still. UK electricity market in a complete mess-- reserve margin about to drop to sub 4% due to phase out of coal stations from EU emission laws (the stations are too small/ old to have scrubbers installed). Foot dragging, plus the lack of policy tools in the post 1990 privatization of the system, means that new capacity has just not been built.

In 2015 the lights are going to start to flicker out. Had we not had the recession (electricity demand is still below 2007) then the Olympics this summer would have seen brown-outs. Embarassing.

I do track the UK power curve (we don't have smart meters-- yet) to try to time laundry loads etc. with relatively 'green' periods (although if I tried to do them over night, I'd be shortly divorced ). I expect within a few years that will be a household financial necessity. Could shoot the Bosch engineer who thought that a 'I am finished' warning buzz, repeated, no shutoff, was a great new 'feature' on the washing machine .

http://www.earth.org.uk/_gridCarbonIntensityGB.html