Oil use per heating degree days

I'm on a similar quest. How big is your house?

sounds perty good to me, .1gal/ degree day =10,000 btu per degree day (if you assume you net 100,000btu/gal, might be more) divided by 24 hours in a day is about 400 btu per degree per hour, which is awfully good for such a big place. You could do a heat loss calculation with your wall types, areas etc. and compare that result with your oil usage or the 400btu/degree/hour to get an estimate of your air leakage and the fudge factor in your estimates.

The hard part might be estimating your wood usage, wood efficiency and hot water usage. Then theres also the electrical contribution and solar gain for south facing windows if you want to account for those.

Along the same lines....we can take your usage divide by HDD, and divide by your square footage, to get 11,000 BTU (0.1 gal net output at 80% eff) / 3100 sq ft = 3.55 BTU/ft^2 degday 'specific heating demand'. This is actually very good, a 'Passivhaus', usually scores ~ 1 BTU/ft2 dday demand. You are using about 3.5X more energy to heat than a passive house, stated another way, your appliances and body heat can probably provide 1/3.5, or almost 30% of your space heating requirement. Of course, it is likely that your true 'demand' is actually ~3.55+1 = 4.55, and you are getting 20-25% from solar gain, body heat and appliances. As I understand it, the housing stock in the US varies from about 5-15 on this scale, with the median around 10 or so. Very few are 5, usually in very cold climates and special designs, and the 15s are usually in the south, 19th century, folks on hearth.com, etc.

Bottom line: you are probably 4-5x the loss of a passivhaus building and better than 95+% of houses in the US.

The 60s split level I bought in 2005 started out ~12, and I have now beaten that down to ~8, without doing any big ticket stuff, just DIY airsealing and weatherstripping.

A question: Are you super air tight? If so, you might want to think about an HRV/ERV.

If you have a good southern exposure and you like to tinker, you could build a solar air heater and take more of a chunk out of the oil use. Another idea would be to add a low mass sun space on the southern side of the house. This could be as simple as closing in a porch with windows or plastic and opening the house windows into the porch when it's sunny.

woodgeek said:

Along the same lines....we can take your usage divide by HDD, and divide by your square footage, to get 11,000 BTU (0.1 gal net output at 80% eff) / 3100 sq ft = 3.55 BTU/ft^2 degday 'specific heating demand'. This is actually very good, a 'Passivhaus', usually scores ~ 1 BTU/ft2 dday demand. You are using about 3.5X more energy to heat than a passive house, stated another way, your appliances and body heat can probably provide 1/3.5, or almost 30% of your space heating requirement. Of course, it is likely that your true 'demand' is actually ~3.55+1 = 4.55, and you are getting 20-25% from solar gain, body heat and appliances. As I understand it, the housing stock in the US varies from about 5-15 on this scale, with the median around 10 or so. Very few are 5, usually in very cold climates and special designs, and the 15s are usually in the south, 19th century, folks on hearth.com, etc.

Bottom line: you are probably 4-5x the loss of a passivhaus building and better than 95+% of houses in the US.

The 60s split level I bought in 2005 started out ~12, and I have now beaten that down to ~8, without doing any big ticket stuff, just DIY airsealing and weatherstripping.

A question: Are you super air tight? If so, you might want to think about an HRV/ERV.

Click to expand...

Thanks for that information. Our new loghome in the Idaho Rockies appears to roughly fall into the same performance category as Antioil's home although we still should be able to improve the insulation quite a bit further.

This time of the year our average temp difference seems to be approx. 50 degrees. We try to keep indoors temperature at 68 F while historical outdoor averages vary between a high of 31 F during the day to a low of 6F at night.

On a sunny day, however, our whole house electric consumption drops from ~ 200 kWh or so to ~120 kWh during the hours that the sun shines into the big (~ 200 sq ft window surface) south-facing prow. Electric is our only power source and provides for heating as well as cooking, lighting and electric appliances plus communications devices and entertainment equipment.

Nonheating electric power usage has not yet been calculated but probably runs at about 40 kWh per day. On the other hand, nearly all electric usage contributes secondarily to heating (with the exception of lighting losses through the windows), so I am not sure how to calculate that in even if I would know it more precisely.

The heated square footage must be about 2200, not counting the largely unheated basement.

I am primarily bringing all of this up to show Antioil that the advice he has been given in this thread to add some type of solar energy capturing spaces or devices seems to be spot on, especially given the fact that he does not want to make large investments, e.g. for heat pumps, etc.

Henk

I couldn't agree more on the solar point. IF you have decent southern exposure, either high performance vertical windows or a separate sun space (with lower window performance) can provide significant heat input. While I am a fan, I think that there are some limits to what this approach can provide...

In most retrofit applications (i.e. no massive thermal storage) most of these approaches can provide at most about 20% of heating needs. If it was sunny every day, a flat plate collector would get a 25% capacity factor. That is, its total energy output is its max output power times 6 hours. On the east coast in winter, about 50% of heating days are sunny, getting down to 12%. So, if you had enough collector (and enough house insulation) to get 100% of your heat from solar, at noon and typical winter temps, then on average, the solar would reduce your energy bill ~12%. IF you go larger, tolerating a little extra heating and temp swing above setpoint during the afternoon, you can get more, but might overheat in the fall and spring, but that could be controlled by pulling a shade, closing a vent, etc. Having collectors along SW/SE directions might help a little, too. In retrofit apps, though, you might get 15-20% tops.

Interestingly, the Passivhaus movement grew out of the (american) passive solar house expts of the 70s. In passive solar design, if you grow the window area and thermal storage with modest insulation, you get large temperature swings and still need a lot of backup on cloudy days. If instead you grow the insulation with modest solar collection and no special storage, the heat you get from the smaller windows goes further, the temp swings are smaller even with the natural thermal storage of the structure, and the amount of backup you need goes way down. IOW, seal and insulate the heck out of your house, and it can become a better passive solar house (in terms of % solar heating, temp swing control, needed backup) than poorly designed solar houses of the 70s.

For me, getting an additional 10% of my heat from a fairly massive and visible and $$ retrofit on my house seems like poor ROI. I can get 10% savings in a couple weekends DIY insulation and airsealing. The more I do this, the more passive solar I am getting (as a %) with my existing windows, and the less I care about my bill for conventional heat. Another issue--as a HP user a BTU on a warm sunny day is a lot cheaper than a BTU on a cold winter night. If I saved 10% of my BTUs using solar during the day, I would realize ~6-7% savings on my bill. In my case, a moot point anyways--I am on the north side of a wooded hill--my winter solar input is all branch filtered.

That said, I love PyMS' house with the 'prow'. Do you get a lot of winter sun in your location (>50%)? IT seems that it would be straightforward to track the difference in elec between a sunny day and a cloudy day at the same outside temperature, or HDD. I wouldn't worry about the artificial light escaping the house as an error term in your energy balance--it should be negligible. Even CFLs turn <15% of the elec into visible light energy.

woodgeek said:

I couldn't agree more on the solar point. IF you have decent southern exposure, either high performance vertical windows or a separate sun space (with lower window performance) can provide significant heat input. While I am a fan, I think that there are some limits to what this approach can provide...

In most retrofit applications (i.e. no massive thermal storage) most of these approaches can provide at most about 20% of heating needs. If it was sunny every day, a flat plate collector would get a 25% capacity factor. That is, its total energy output is its max output power times 6 hours. On the east coast in winter, about 50% of heating days are sunny, getting down to 12%. So, if you had enough collector (and enough house insulation) to get 100% of your heat from solar, at noon and typical winter temps, then on average, the solar would reduce your energy bill ~12%. IF you go larger, tolerating a little extra heating and temp swing above setpoint during the afternoon, you can get more, but might overheat in the fall and spring, but that could be controlled by pulling a shade, closing a vent, etc. Having collectors along SW/SE directions might help a little, too. In retrofit apps, though, you might get 15-20% tops.

Interestingly, the Passivhaus movement grew out of the (american) passive solar house expts of the 70s. In passive solar design, if you grow the window area and thermal storage with modest insulation, you get large temperature swings and still need a lot of backup on cloudy days. If instead you grow the insulation with modest solar collection and no special storage, the heat you get from the smaller windows goes further, the temp swings are smaller even with the natural thermal storage of the structure, and the amount of backup you need goes way down. IOW, seal and insulate the heck out of your house, and it can become a better passive solar house (in terms of % solar heating, temp swing control, needed backup) than poorly designed solar houses of the 70s.

For me, getting an additional 10% of my heat from a fairly massive and visible and $$ retrofit on my house seems like poor ROI. I can get 10% savings in a couple weekends DIY insulation and airsealing. The more I do this, the more passive solar I am getting (as a %) with my existing windows, and the less I care about my bill for conventional heat. Another issue--as a HP user a BTU on a warm sunny day is a lot cheaper than a BTU on a cold winter night. If I saved 10% of my BTUs using solar during the day, I would realize ~6-7% savings on my bill. In my case, a moot point anyways--I am on the north side of a wooded hill--my winter solar input is all branch filtered.

That said, I love PyMS' house with the 'prow'. Do you get a lot of winter sun in your location (>50%)? IT seems that it would be straightforward to track the difference in elec between a sunny day and a cloudy day at the same outside temperature, or HDD. I wouldn't worry about the artificial light escaping the house as an error term in your energy balance--it should be negligible. Even CFLs turn <15% of the elec into visible light energy.

Click to expand...

All very informative and well-reasoned, I think. I learned a lot!

My guess is that, just over the past 2 years, almost 2 out of 3 winter days were at least partially sunny. However, I haven't found official data yet.

Henk

Yah, I think I was a little too enthusiastic with my numbers...your low oil usage is an unknown combination of your insulation and your wood usage. If we took your 900 gal usage from a couple years ago divided by your 6000 degree days, we get 0.15 gal/dday, or 50% higher than I assumed. Recrunching the numbers, we get that your specific demand, per sq ft, is at least 3.55*1.5 = 5. Since you likely had some background heat from your boiler, appliances, etc, your demand is probably at least 1 more than that, or '6'. So if you you did not burn much wood in 2008, your demand score then was '6', If you did and got half of your heat, your score is 11, worse than average. IOW, it is impossible to say 'how good your doing' on insulating your house, or what fraction of heat comes from wood w/o a little more info.

So, how much wood did you burn last year along with 700 gals oil? I would score one cord as ~160 gals oil. Is your reduction from 2008 due to insulation/airsealing, or burning a couple cords/yr.

So, what I should have asked was age of house, whether it has been airsealed, what the R-value in the attic is, quality of door and window weatherstripping, etc. It is quite possible that there is some low hanging fruit to reduce your demand further w/o on less that a $1000 budget....lot's of folks here have advice about such things...

Don't despair. This whole house tightening thing has really been a challenge for me too. The first couple years I walked around an said 'I feel a draft here' and eliminated it, and thought I was making great progress. I wasn't. Since then I have been researching more and taking a more systematic approach (mostly on the airsealing side, as my home is mostly insulated to a 80s standard), and I have gotten about a 30% reduction.

Along the way, I realized its not all about $$, there is also comfort. I am sure your insulation investment will pay off eventually, even if you can't 'see' its effect in your usage, and has made your house more comfortable to boot. Usage numbers are noisy and just estimates--you can get a 10% reduction and miss it easily, esp with fewer people in the house and changing appliance usage patterns...

IF you are feeling overwhelmed about where to start, that is what energy audits are for--they will tell you what is up, what you can do, and estimate the savings for each thing. Or tell you that you're doing pretty well, and you can obsess about something else... I haven't dropped the coin for an audit yet cause I'm a stubborn cuss--but will when I run out of things to improve.

And at 1000 gals/6000 ddays = 0.166 gal/dday = 18300 BTU/dday = 5.9 BTU/ft2.dday. With background contributions, you are likely closer to '7'. If my memory is correct, and US housing stock is a bell curve 10±5, you are likely better (lower) than 70% of houses (on a per sq ft basis), nothing to sneeze at.

woodgeek said:

I couldn't agree more on the solar point. IF you have decent southern exposure, either high performance vertical windows or a separate sun space (with lower window performance) can provide significant heat input. While I am a fan, I think that there are some limits to what this approach can provide...

In most retrofit applications (i.e. no massive thermal storage) most of these approaches can provide at most about 20% of heating needs. If it was sunny every day, a flat plate collector would get a 25% capacity factor. That is, its total energy output is its max output power times 6 hours. On the east coast in winter, about 50% of heating days are sunny, getting down to 12%. So, if you had enough collector (and enough house insulation) to get 100% of your heat from solar, at noon and typical winter temps, then on average, the solar would reduce your energy bill ~12%. IF you go larger, tolerating a little extra heating and temp swing above setpoint during the afternoon, you can get more, but might overheat in the fall and spring, but that could be controlled by pulling a shade, closing a vent, etc. Having collectors along SW/SE directions might help a little, too. In retrofit apps, though, you might get 15-20% tops.

.

Click to expand...

Hi,

I agree totally with your statements about air sealing and insulation...that will ,by far, get you the biggest bang for the buck. However, installing a hot air solar collector sized 10% of the square footage you want to heat can get you a larger percentage than you are stating above. I currently am getting approx 25% of my heat using a 96 sq ft collector to heat approx 1000 sq ft. The collector dumps heat into my cellar where my wood stove is located (I am not including the area of my unfinished cellar in the calculations...just the 1000 sq ft living area upstairs. There's also a 750 sq ft 2nd storey that we keep very marginally heated). This is with no storage other than the house itself, in a very marginal solar area near Ithaca,NY. My house is an 1840's timberframe...not exactly the tightest building around, although I've done a lot over the years to make it tighter and better insulated. If you use a hydronic solar collector with properly sized storage, you can do much better than this, but there's a price point for everything, where it may not be worth the cost to to get more heat. I just don't want people to think that there's not much to be gained with a solar installation, especially a DIY project, because there is. It works even in my less than optimal solar area.

antioil said:

My sincerest thank you for some of the most useful and very intelligent information this post provided. I asked a pretty basic question and now I think I'm ready to go over to MIT. I really appreciate it.

Actions already taken as a result of posts:

Is my home super tight? (From Woodgeek)

No not really and several things I have been intending to do finally got done. I purchased some plastic vent covers for the central AC system I put in 6 years ago. These covers go over the inside vents. On the larger return vents ( the ones with the filters) I wrapped the filters in plastic. ( I am embarrassed that I didn't do all this sooner) 6 covers about $100. Each cover took about a minute to install.
I think I could spend much more time going around with a caulk gun and insulation to "seal" rooms a lot more. I will never underestimate sealing all those "little" things, to keep rooms tighter again.

Use solar:

My home is a long ranch running east to west. The back has 100 percent southern exposure. And because it has a full shed dormer on the south side and a walk out basement too I have 3 stories with southern exposure. The north side ( front) looks like a one level ranch. I am zeroing in on a breezeway between the garage and our den where we spend most of our time and has the thermostat for one half of the first floor zone. So when the door is opened while exiting and entering heat is obviously lost thus causing a call for heat when the rest of the zone really doesn't need it. I may go over my 1,000 limit but if I change out the 60+ year old casement windows on the south side (and insulate) and do something really tight on the north side of the breezeway then the den opens and closes into a warmer area. I think you called it a sun space. When the sun was finally out yesterday that area was over 60 degrees when the outside temp was in the 20's. As soon as the sun goes down ( or a breeze blows) this area is like being outside. That would be huge (I think)

Well thanks again and I'll share with you any additional noticeable improvements.

Click to expand...

Hi,

some other ideas for you:

Can you add more insulation in a crawl space or attic above? Cellulose is cheap and you can easily blow it in yourself. It'll make a huge difference.

Just installing acrylic inside storms over windows held in place with velcro will give you almost the same benefits as if you replaced the windows...new windows are definitely nice but can be a long payback.

As far as the solar stuff goes, it looks like you may have a great location. There's lots of good solar and energy conservation info here:

http://www.builditsolar.com/

Also lots of good info and help in the 2 solar groups below:

http://tech.groups.yahoo.com/group/SimplySolar/
http://tech.groups.yahoo.com/group/SolarHeat/

Good luck!

sesmith said:

Hi,

I agree totally with your statements about air sealing and insulation...that will ,by far, get you the biggest bang for the buck. However, installing a hot air solar collector sized 10% of the square footage you want to heat can get you a larger percentage than you are stating above. I currently am getting approx 25% of my heat using a 96 sq ft collector to heat approx 1000 sq ft. The collector dumps heat into my cellar where my wood stove is located (I am not including the area of my unfinished cellar in the calculations...just the 1000 sq ft living area upstairs. There's also a 750 sq ft 2nd storey that we keep very marginally heated). This is with no storage other than the house itself, in a very marginal solar area near Ithaca,NY. My house is an 1840's timberframe...not exactly the tightest building around, although I've done a lot over the years to make it tighter and better insulated. If you use a hydronic solar collector with properly sized storage, you can do much better than this, but there's a price point for everything, where it may not be worth the cost to to get more heat. I just don't want people to think that there's not much to be gained with a solar installation, especially a DIY project, because there is. It works even in my less than optimal solar area.

Click to expand...

I wouldn't want to discourage anyone from trying stuff--perhaps make them realistic about output for a given configuration....

Your collector at ~10 m^2 is rather large, and it sounds like you are using the mass of your foundation to provide effective storage in an 'active solar' configuration. 25% sounds impressive but possible, how do you determine this? How big are your temp swings (in the living space)? Is control difficult?

Most of the (poorly planned) DIY systems I've heard of had undersized collectors, and inadequate CFM airflow, small ducting etc. I would think a 10 m^2 system would need a lot of cfm, and either a big honking duct or several smaller ones. Perhaps you want to describe your system in more detail?

woodgeek said:

Your collector at ~10 m^2 is rather large, and it sounds like you are using the mass of your foundation to provide effective storage in an 'active solar' configuration. 25% sounds impressive but possible, how do you determine this? How big are your temp swings (in the living space)? Is control difficult?

Most of the (poorly planned) DIY systems I've heard of had undersized collectors, and inadequate CFM airflow, small ducting etc. I would think a 10 m^2 system would need a lot of cfm, and either a big honking duct or several smaller ones. Perhaps you want to describe your system in more detail?

Click to expand...

Hi,
I got the 25% figure by comparing fuel usage to heat the house without the collector vs. fuel usage the year I put the collector in and factored in the difference in heating degree days for the 2 heating seasons. Temp swings are moderated by the fact that both my wood stove and the solar heater dump their heat into my unfinished stone cellar, and we move the heat up from there. Maybe not the most efficient way to heat, but due to the floor plan, it works out ok. We are pretty tough though Have been heating with wood for years, and anything between 63 and 72 is good. The main difference I've noticed with the solar collector, is that when I come home from work on a cold sunny day, the house is 69-70 instead of 63 as the fire in the stove has died down. Much less need, then, to play catch up with the wood stove or turn on the furnace to warm things up (I think I only used around 20 gal of heating oil last year and less than that so far this year). During the shoulder seasons, the collector heats the house without any help from the wood stove (so long as the sun shines). Our main problem around here is the lack of sun, but there's actually more than I give the area credit for. Details on my collector can be seen here:

http://www.n3fjp.com/solar/solarhotair.htm

Mine is the larger one partway down the page labeled "Scott S enhanced". Details and pics of the build are further down the page with some performance data I took. I did have a problem with slightly undersized ducts (didn't do my homework well enough). It would have been a lot of work to put in larger ones, so I put a 2nd blower in parallel which comes on when the outlet temp of the 1st blower is around 120 degrees. This helped...not an ideal fix, but the collector works great as is.