prioritizing energy savings - spray foam vs. wood stove

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twd000

Feeling the Heat
Aug 28, 2015
448
Southern New Hampshire
I'm trying to decide where to invest my dollars to save money on the "whole picture" of my home's energy use.

It's a 1974 colonial in Southern New Hampshire, USDA Zone 4. 3000 square feet of conditioned space. Propane furnace in winter, central air conditioning used sparingly in the summer. At current energy prices, yearly total spending is about
$1600 electricity
$900 water heating
$1900 space heating

I estimate I'm using 60 MBTU per year for space heating. I think it is reasonably well insulated, new windows etc. But I don't believe any effort was made for air-sealing the attic, basement, top plates, plus all the little passthroughs for bathroom vents, HVAC ducts, etc.

So I'm trying to evaluate two projects:
  • Removing all the fiberglass and cellulose attic insulation and having it sprayed with closed-cell spray foam. There are two rooflines, with 1400 sq ft total attic space. My ballpark estimate is $8,000 for 6" R-42 equivalent.

  • installing a Blaze King King in the main living floor, plus stainless liner and some non-trivial chimney modification. I'm estimating $6,000.
Of course I'll get professional estimates once I decide which project to proceed with.
My payback estimate on the stove is 4-5 years. Has anyone gone down the road of spray foam in existing construction, to estimate the payback period? And how much I should expect my yearly MBTU to be reduced? The spray foam is appealing because it helps during heating and cooling season. But I don't know if the marginal efficiency increase is justified.
 
I'm trying to decide where to invest my dollars to save money on the "whole picture" of my home's energy use.

It's a 1974 colonial in Southern New Hampshire, USDA Zone 4. 3000 square feet of conditioned space. Propane furnace in winter, central air conditioning used sparingly in the summer. At current energy prices, yearly total spending is about
$1600 electricity
$900 water heating
$1900 space heating

I estimate I'm using 60 MBTU per year for space heating. I think it is reasonably well insulated, new windows etc. But I don't believe any effort was made for air-sealing the attic, basement, top plates, plus all the little passthroughs for bathroom vents, HVAC ducts, etc.

So I'm trying to evaluate two projects:
  • Removing all the fiberglass and cellulose attic insulation and having it sprayed with closed-cell spray foam. There are two rooflines, with 1400 sq ft total attic space. My ballpark estimate is $8,000 for 6" R-42 equivalent.

  • installing a Blaze King King in the main living floor, plus stainless liner and some non-trivial chimney modification. I'm estimating $6,000.
Of course I'll get professional estimates once I decide which project to proceed with.
My payback estimate on the stove is 4-5 years. Has anyone gone down the road of spray foam in existing construction, to estimate the payback period? And how much I should expect my yearly MBTU to be reduced? The spray foam is appealing because it helps during heating and cooling season. But I don't know if the marginal efficiency increase is justified.
I say go for the King! My grandkids need a college fund!
 
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Well I know you wouldn't want your grandkids to get spoiled, so how about I pay them $15/hour to come spray foam my attic!? ;)
 
What would be your source of wood? Purchased or home cut, split and stacked? If home C/S/S do you already have the equipment to do this?

How much insulation is currently in the attic?
 
Its a no brainer, insulate first and then install a stove. The best BTUs are the one you don't have to burn. Look into this program and get the utility to pay for a big chunk of it
http://www.nhsaves.com/save-home/save-more/energy-audits-weatherization/. I did flash and bat on half my attic, it was fairly new insulation so I pulled it and had them spray about 3" of foam then put the insulation back in place with a second layer running cross ways to the first. On the other side they pulled the fiberglass in few spots but mostly sealed few light fixtures. The only down side is I lost attic storage space as the insulation is up on the rafters. One of these days I will probably put in elevated gangplanks. The biggest bang for the buck was they sprayed my basement sills and sealed some can lights.

Next thing is find a wood supply a year to two years before you buy a stove and get it cut split and piled up and dying, then watch craigslist and uncle henry's for the suckers who are yanking out new stoves thinking the cost for oil or gas is going to stay low (or were trying to burn green wood with an EPA stove).
 
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Well I know you wouldn't want your grandkids to get spoiled, so how about I pay them $15/hour to come spray foam my attic!? ;)
Hey, that's minimum wage in Seattle. My 4 year old granddaughter would do it in a heart-beat...and her 7 year old brother would watch her!
 
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What would be your source of wood? Purchased or home cut, split and stacked? If home C/S/S do you already have the equipment to do this?

How much insulation is currently in the attic?

I would estimate there is an average of 12" of insulation across the attic. It's pretty haphazard. I assume all the rafter bays are filled with fiberglass, then there is some blown in cellulose on top of that in some areas, but not others. Some areas also have batts laid crosswise on top of the other batts.

I am looking at having log length cord wood delivered at $125 a cord. I was surprised at how little scrounging shortened the payback period. Yes I have all the equipment to process it onsite, and I have about 3 cords ready to go.
 
Its a no brainer, insulate first and then install a stove. The best BTUs are the one you don't have to burn. Look into this program and get the utility to pay for a big chunk of it
http://www.nhsaves.com/save-home/save-more/energy-audits-weatherization/. I did flash and bat on half my attic, it was fairly new insulation so I pulled it and had them spray about 3" of foam then put the insulation back in place with a second layer running cross ways to the first. On the other side they pulled the fiberglass in few spots but mostly sealed few light fixtures. The only down side is I lost attic storage space as the insulation is up on the rafters. One of these days I will probably put in elevated gangplanks. The biggest bang for the buck was they sprayed my basement sills and sealed some can lights.

Thanks for the program info. Can you give me some numbers on your project? Energy usage before and after?
 
I would estimate there is an average of 12" of insulation across the attic. It's pretty haphazard. I assume all the rafter bays are filled with fiberglass, then there is some blown in cellulose on top of that in some areas, but not others. Some areas also have batts laid crosswise on top of the other batts.

I am looking at having log length cord wood delivered at $125 a cord. I was surprised at how little scrounging shortened the payback period. Yes I have all the equipment to process it onsite, and I have about 3 cords ready to go.
Sounds like you know the riff and are ready for wood heat. Both options are going to return nice gains. I'd be tempted to insulate first for year round benefit and put in a <$1000 stove now like the Drolet Myriad or Englander 30NC. Upgrade in a few years as the budget permits.
 
Sounds like you know the riff and are ready for wood heat. Both options are going to return nice gains. I'd be tempted to insulate first for year round benefit and put in a <$1000 stove now like the Drolet Myriad or Englander 30NC. Upgrade in a few years as the budget permits.
Yes, this ^ ^ ^
 
I really cant give you true payback on my project as I had a couple of other energy projects that were done in at the same time. I live in northern NH and have not filled my oil tank in three years. I use a minisplit for my only heating source when averages temps are around 30 and used 3.5 cords last year and around a cord and half this winter. I generate excess electric power with my solar but figure I use about 1800 kw for the minisplit.

The nice thing with the NH program is the utility audits the work and the contractor does a pre and post blower door test. When they do the audit they will hand you the report with the payback for each improvement. The biggest payback is air sealing.
 
Any opportunity to connect your furnace to natural gas?

Conservation versus woodstove: with the first, get it done and enjoy; if you install a stove the work is only beginning.
If you take all the time and money you'd spend heating with wood and instead seal and insulate the house you'll be way ahead in a few years with lasting benefits. You can then install a smaller wood stove, HP, whatever for heating.
 
Think of all the exercise you will get cutting, splitting and stacking...and then loading too! Heck, you're saving the money a gym membership would cost you.
 
I would estimate there is an average of 12" of insulation across the attic. It's pretty haphazard. I assume all the rafter bays are filled with fiberglass, then there is some blown in cellulose on top of that in some areas, but not others. Some areas also have batts laid crosswise on top of the other batts.

I am looking at having log length cord wood delivered at $125 a cord. I was surprised at how little scrounging shortened the payback period. Yes I have all the equipment to process it onsite, and I have about 3 cords ready to go.

12" of cellulose and/or fibreglass puts your R value in the mid 30's. (both fiberglass and cellulose have an R value slightly over R3 per inch). If it were me, I'd have additional cellulose blown in to have even insulation in the whole attic and correct those 'haphazard' areas. At a fraction of the cost of spray foam.
Then add your stove.
 
Changing the attic insulation won't do anything. Sealing the attic will only cause moisture problems. The reason people always harp about attic insulation is because it's accessible. Even a poorly insulated attic, say 6" fiberglass, only accounts for 20% heat loss.
 
Any opportunity to connect your furnace to natural gas?

Conservation versus woodstove: with the first, get it done and enjoy; if you install a stove the work is only beginning.
If you take all the time and money you'd spend heating with wood and instead seal and insulate the house you'll be way ahead in a few years with lasting benefits. You can then install a smaller wood stove, HP, whatever for heating.

no natural gas available in my area; most people with propane installed it for backup generators, then switched their furnace from oil to propane. It looks like prior owners of my house took the same approach.

Yes, the passive aspect of air sealing is appealing. I'm looking into the audit/rebate now
 
I really cant give you true payback on my project as I had a couple of other energy projects that were done in at the same time. I live in northern NH and have not filled my oil tank in three years. I use a minisplit for my only heating source when averages temps are around 30 and used 3.5 cords last year and around a cord and half this winter. I generate excess electric power with my solar but figure I use about 1800 kw for the minisplit.

The nice thing with the NH program is the utility audits the work and the contractor does a pre and post blower door test. When they do the audit they will hand you the report with the payback for each improvement. The biggest payback is air sealing.

I assume you meant 1800 kWh for the minisplit heat pump? If so that is about 10% of my yearly MBTU consumption. Plus 3.5 cords of oak (22 MBTU/cord , 70% efficiency) is another 110 MBTU. You're definitely in a colder climate, and last winter was extreme.

I just ran the calculator at NHSaves.com. It reports that my current propane consumption (20k BTU/sq ft) s already very efficient, and therefore I'm not eligible for audit/weatherization rebates. I had to bump consumption up to 200 gallons/year to get into the inefficient zone of their calculator. There must be some really leaky houses around here!
 
12" of cellulose and/or fibreglass puts your R value in the mid 30's. (both fiberglass and cellulose have an R value slightly over R3 per inch). If it were me, I'd have additional cellulose blown in to have even insulation in the whole attic and correct those 'haphazard' areas. At a fraction of the cost of spray foam.
Then add your stove.

This is the answer. You already have better attic insulation than most. Moving up from mid R30s to R42 by removing your existing is a bad idea IMO. If you are just dying to get more R-value you can blow in more cellulose. I bet your walls are 2x4 construction with R-5 batts, R-13 at best. That's where you can increase the R-value that has some payback.
 
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12" of cellulose and/or fibreglass puts your R value in the mid 30's. (both fiberglass and cellulose have an R value slightly over R3 per inch). If it were me, I'd have additional cellulose blown in to have even insulation in the whole attic and correct those 'haphazard' areas. At a fraction of the cost of spray foam.
This is the answer. You already have better attic insulation than most. Moving up from mid R30s to R42 by removing your existing is a bad idea IMO. If you are just dying to get more R-value you can blow in more cellulose. I bet your walls are 2x4 construction with R-5 batts, R-13 at best. That's where you can increase the R-value that has some payback.
This does nothing for air sealing (isolating attic from living space) though which could well be your biggest heat loss because of stack effect.
 
Bummer on the lack of rebate money, I was on the edge when I took advantage. You are correct 1800 KWhr. Even if the state wont do it, looks around for an organization with blower door. This group has one in Plymouth http://www.plymouthenergy.org/. Alternatively I expect you could rig up large house fan with tarp over the door opening. It really impressive how depressurizing a house on cold day shows where the leaks are. I finished a large master bedroom about 10 years ago and thought I did good job, once the blower was on I found that I had air coming in under the outerwall sills and my outlets. Of course I was also sucking air down the chimney.

They had to install a fan timer on my bathroom to force more air changes to meet indoor air quality. Its taken several years but I just bought a Fantech HRV and am in the process of collecting parts to install it.

Come on up to the Berlin, a lot of the old rental units have little or no insulation or poorly pumped in cellulose. Many have single pane windows and wooden doors with no weather stripping. Insulation is important but infiltration is the killer, A closed door with no weather-stripping is equivalent of good sized hole in the wall . A friend just built a Passivhaus in Portland Maine, its amazing the extent they had to go to seal the envelope so they are darn close to zero infiltration. They bring it way down and then add back in air where they need it via a HRV.
 
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This does nothing for air sealing (isolating attic from living space) though which could well be your biggest heat loss because of stack effect.

What I've done is complete the air sealing with the old insulation in place and then add additional cellulose to R-50. Sure, full spray foam is superior but at a ridiculous cost for an attic with access.
 
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3000 square feet of conditioned space....
$1600 electricity
$900 water heating
$1900 space heating
I estimate I'm using 60 MBTU per year for space heating.
What are your electric rates?

By far, the least expensive energy saving is conservation. I would recommend that you consider pursuing conservation with a vengeance, something my wife and I have done. We also are in USDA Zone 4 and 3000 square feet of conditioned space, all electric house except wood stove in the living room.

$420 electricity for domestic hot water and space heating (6,000 kwh)
$600 for general service electricity (5,000 kwh)
4 cords of aspen stove wood for space heating, c/s/s from our land, about $700 if we would buy c/s (equivalent to about 16,000 kwh)

We don't actually pay for that electricity, as 100%+ of our electricity is provide by our solar PV system.
 
What I've done is complete the air sealing with the old insulation in place and then add additional cellulose to R-50. Sure, full spray foam is superior but at a ridiculous cost for an attic with access.
Which is exactly what I think the OP should consider doing. Agreed on the spray foam. My point was that adding more thermal insulation without air sealing wasn't the right course. The problem is working around all the insulation already in place - not fun.
 
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What are your electric rates?

By far, the least expensive energy saving is conservation. I would recommend that you consider pursuing conservation with a vengeance, something my wife and I have done. We also are in USDA Zone 4 and 3000 square feet of conditioned space, all electric house except wood stove in the living room.

$420 electricity for domestic hot water and space heating (6,000 kwh)
$600 for general service electricity (5,000 kwh)
4 cords of aspen stove wood for space heating, c/s/s from our land, about $700 if we would buy c/s (equivalent to about 16,000 kwh)

We don't actually pay for that electricity, as 100%+ of our electricity is provide by our solar PV system.

Total effective electric rate is $0.17/kWh
Here are my numbers in kWh for comparison:
space heating: 18,000 kWh (propane source)
water heating: 9,000 kWh (propane source)
electricity: 9,600 kWh

Wow how did you get your electricity use that low?! I'm 2x your usage. I was thinking of trying one of those Energy Detective devices to identify and reduce my base load.
 
A question....did the OP want to sprayfoam the attic floor to get better airsealing, under the existing insulation, and then up the insulation to R-50 as needed (and keep the attic vented) OR to sprayfoam the roofline sealing the attic?

Also...there is HVAC in the attic, or just a couple ducts?

I would say that 60 MMBTU for 3000 sq ft in that climate is prob 3-4 BTU/sqft.degreeday, already better than I **guess** 80% of american homes.
 
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