Most efficient home heating question?

System · February 2008

Hello guys and i want to again say thanks to all who tirelessly post replies to those of us who seemingly ask all the same questions =P Never-the-less the question im asking i didnt see quite worded in another post with a direct answer, which i know its more a matter of opinion.

My question is:

I am wondering if there is a collection of thoughts on efficient home heating techniques for off-the-grid systems in remote locations. Lets also assume the worst case scenario of high temperature differentials of like -5F to 80F.

I do plan on using very highly efficient building materials like RASTRA and or others that present themselves before time however how i design the entire home is completely considered (no stone un-turned). My first impressions were water based baseboard heating or in-floor water based heating as i could opt for solar water heating on roof panels.

One last consideration is that i am trying to limit the amount of supplies required for the upkeep of the home like natural gas deliveries etc so if you happen upon some solutions you think i should consider the fire away!

thanks so much for your consideration guys, i know blasting away at some of these silly questions can get boring and i can only offer this great big THANKS in recompence for all your sometimes unrecognized efforts.

PS, if you know a bit about voltages and their benefits IE 12/24/48/96 and pros/cons zip on over to the General Solar Questions forum and flex those muscles... theres a box of cookies waiting over there for you!

niel · February 2008

Re: Most efficient home heating question?

you are right, that is a different take on things and most are not going for the most efficient, but are trying to go for the most cost efficient and with today's marketplace that changes oh so much. it really doesn't matter about the btu's produced as efficiently as possible as long as they are produced. that natural gas may be the cheapest cost to me, but if trucked to you i would say not due to trucking costs. the real trick is keeping the heat produced as long as possible, but that we have covered. for most country or remote living you need a reliable source of fuel and that is usually wood. some have solarly backed that up too with the solar passive heating and the various ways of doing that. for best comfort and safety i'd say get a seperate from the home woodburning hot water system, but do you want to trudge outside several times a day to feed the fire? i also don't know all pros and cons of that setup, but rest assured it's high priced. the simplest is a centrally located sealed fireplace or woodburner. higher efficiency really means more heat extracted from the heat source and no particular method is overall best as even lng and woodburnering furnaces vary in efficiency and is more a question of costs to produce.

mike95490 · February 2008

Re: Most efficient home heating question?

I've heard large mass, masonry fireplace (popular in Europe), is a winner, next may be something like a soapstone stove.
Solar heated hot water is supposed to be a winner too.

icarus · February 2008

Re: Most efficient home heating question?

It is a question, that in my opinion has lots of "right" answers depending on the question. If you are asking, what uses the fewest gross BTU's for total heating that is one question. If the question is which uses the fewest carbon based BTU's that is another. If the question is what is the true life cycle BTU count including the hidden BTU's of construction, transport, recycling and disposal at end of cycle that is yet another. The list could go on and on.

Once again, in my opinion the most efficient starts with asking the right question and looking into proper design. It is one thing to be cutting edge efficient with a X thousand square foot McMansion, and quite another to be quite efficient with a more modest structure.

Super insulation, air to air heat exchange, proper window and door design to take advantage of passive solar heating (and cooling) earth sheltering, and on to active solar domestic water and space heating. All these items are much cheaper up front rather than in a remodel situation.

Thermal mass systems (hot water especially) are nice for long periods of even heat without temp spikes up or down. On the other hand hot air is nice if you want heat quickly. For example, a house that is only occupied on the weekends, would take a longer time to come up to a comfortable temp with radiant hot water as opposed to forced air. (If you kept the temp down during the week)

I personally like the idea of keeping only the spaces I am in at "normal" temp, say 70f. (This gets a little complicated as we live in 3 rooms in the bush, but we do have a "real house" that we are in sometimes,,sorta the opposite of most people) The rest of the house can vary as low as 50f or lower. I use a combination of wood for the main part of the house, but the breakfast area where we sit most of the time, and is cooler has a Rinnai gas space heater. I can let the fire in the stove go out at night, and the space heater will quickly bring the breakfast area up to temp, without heating the whole house. If we are gone for the day, I might not light a fire until evening. I have another Rinnai in my office for the same reason. I tend not to use the office. When I do, I'll use it all day and heat it then.

I do cheat and keep a wall mounted electric going in the bathroom. I wish I had put radiant heat in the floor when we built it.

I spent a lifetime designing and building custom homes. The only thing most clients had in common was that they didn't think things out enough going in. So many choices are made without regard to "good design" and without regard for the efficiency of the total structure. If you are working with a designer or Architech spend all the time you can thinking about what it is you are trying to achieve.

Good luck

PS. I realize this is a bit of a diatribe,,,sorry,

Tony

System2 · February 2008

Re: Most efficient home heating question?

thanks everyone for your input it is much appreciated.

It looks like in my initial plans that using water based baseboard heating or in-floor heating will be the winner as it provides the ability to heat effectively in both the areas i need and as well as quickly to some degree (more so in baseboard then in floorboard) and this opens me up to solar water heating as well as having a simple wood/coal burning boiler to help augment should it become needed.

Im not fond of the amount of carbons released during the burning of coal so wood will likely be it although i know wood is not really that much better considernig the impact taking from the enviroment has, my hopes are that i can plan solar heating and space heat efficiency well enough that any outside heating sources like woodburning will be minimal.

If anyone has any other thoughts PLEASE share them, i'd love to find a better solution!

mike95490 · February 2008

Re: Most efficient home heating question?

Heres a couple of articles I've had my eye on:

http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm
I don't know if I like all the plywood, making that huge hot water tank.

and another style, less thermal mass
http://www.arttec.net/Solar/10-5/Oct5.html

and a novel heat exchanger "solar wand"
http://www.arttec.net/SolarDHW/index.htm

Hope this helps

Telco · February 2008

Re: Most efficient home heating question?

Ideas, eh? Here's more than you bargained for...

What works best will depend on how you will use the place. If you are going to live there year round, I'd look at dry stack blocks over Rastra. The reasons are, Rastra insulates both sides of the block, dry stack doesn't. Dry stack does require that you insulate one side though, and I would insulate the outside. The idea here is that you have a thermal mass on the inside of the insulation to help regulate temperature in the house. Plus, with rebar and concrete fill in every block hollow, you'd have a super strong house that won't burn. And, (important in my part of the country) a tornado would have to sit on it for days to cause damage. I've also heard of issues with Rastra being hard to get a good fill on from people who do the concrete work, that don't have an interest in selling Rastra blocks. There's also a labor savings as dry stacking can be done by anyone, no special skills needed. For external insulation, I want several inches of spray-on polyurethane. I'm figuring on my initial building, a 20x30 shop, that I'll be able to get the place from prairieland to a functional building for 20 grand. This shop will serve as my residence while I'm building the actual house so I'll be able to forward my current mortgage payments into building supplies. Neat.

Another nice feature of this style of building: to burn the place down you'd have to FORCE it to burn down, as in gallons and gallons of fuel sprayed on everything in the house. It's not going to just accidentally catch fire, even if a wire shorts out. This means much lower insurance rates.

Other ideas, the solar shed that Mike suggested is one I was going to suggest myself. I really love that idea, with a few mods. I'd use evacuated solar tubes instead of the flat panels, as the evacuated tubes will heat water on overcast days. All it needs is light to work, not direct sunlight. And, I'd have a larger water bank, the idea to have a large enough bank to keep the water/antifreeze mix heated to around 200 degrees or so and be able to keep it heated to this temp for 2-3 days in the event of not enough sun to heat the water, before needing to use a backup heating method. You can use this to heat water for household uses, and can use it to heat the place.

I'd use a high efficiency air conditioner with a water heat system. This would allow me to pump the hot water from the water bank through the HVAC system. Saw this used on This Old House, they were retrofitting HVAC to a 200 year old 4 story house and didn't want anything combustible in the attic. This setup looked like a regular HVAC unit, except the inlet had a large radiator like what an automobile would use to put heat into the air.

I wish there were a good hydronic dryer on the market that could use a water/antifreeze mix to dry clothes with. The closest I've seen is a fellow that took an old dryer that wasn't heating anymore, and stack automobile heater cores to heat the air. He said he was able to get it to within 20 degrees or so of what a clothes dryer's electric elements can get to. Might be a possibility.

For hot water, you have to use an isolator to keep the potable water separate from the heated antifreeze mix. Good news is, I saw one on the internet that a fellow was holding, it was about the size of a standard PC case. According to the accompanying article, it was sized for commercial applications, so would be plenty large enough for a house.

I'd also be putting in a power shed on the far side from the water shed, with the PV panels right there. The power shed would hold the batteries, inverters, everything. From there, I'd run 120V to the house. This way, in the future all it would take is having power hooked up if I ever had to go back on the grid. And, wiring losses would be minimized between the panels and batteries. Might even half-bury the battery room, and mount the panels on poles on top of the building. I'd also want to do passive trackers on the panels since this seems to be the best compromise between efficiency and complexity.

I've still got a lot of details to work out, but so far this is my roughed out idea on the ideal "gentleman farmer" place. I've even thought about looking into growing my own corn and converting it to biodiesel, but one hugantic project at a time!

Most of this is pie in the sky dreaming at this point, but I hope it gives you some ideas. I'm gonna try my best to make it all happen.

mike95490 · February 2008

Re: Most efficient home heating question?

Telco wrote: »

I wish there were a good hydronic dryer on the market that could use a water/antifreeze mix to dry clothes with. The closest I've seen is a fellow that took an old dryer that wasn't heating anymore, and stack automobile heater cores to heat the air. He said he was able to get it to within 20 degrees or so of what a clothes dryer's electric elements can get to. Might be a possibility.

I've heard of using the hot, attic air, ducted to the inlet of the clothes dryer, as a low tech way to tumble dry.

icarus · February 2008

Re: Most efficient home heating question?

Clothes line works pretty good too! Low tech, no parasitic energy costs either!
Works indoors and out too!

Icarus

dale · February 2008

Re: Most efficient home heating question?

I was playing with some numbers. A 9.6Kw system in my area should produce about 12,622 KwHrs of electric per year. If half to two thirds was available for heating, would this be enough to significantly lower, or possibly replace, an oil boiler for heat and hot water?

System2 · February 2008

Re: Most efficient home heating question?

Telco,

3/4's of your post were exact ideas i had and i did plan to use a solar shed for the water heating array, as well as buliding a workshop to base my ops from while i build the house then converting my workshop to my utility management, etc / garage perhaps =P.

Lastly i have a question that i havnt quite grasped if anyone would feel like explaining it to me.

Rastra insulates both sides, it was always my thought that insulation isnt bad the more you have, secondly if dry block only insulates one side wont some of the energy used to heat the home be lost absorbing into the block (although not escaping out the other side?) i dont know, this rastra stuff confuses me, but as for the challenges it presents laying it im not worried i have a relative who works with concrete in the area im looking to build so thats not a problem, they have already assured me they have the experience and qualifications to work with that material.

i dont mind having to choose block over rastra as i have masonry skills in laying block as well but i just wanted the best solution possible.

Lastly, if rastra insulates both sides, would it be better used in the solar shed application for the water storage area, creating a rastra pen to house the water tank to store the hot water?

fire away!

icarus · February 2008

Re: Most efficient home heating question?

dale wrote: »

I was playing with some numbers. A 9.6Kw system in my area should produce about 12,622 KwHrs of electric per year. If half to two thirds was available for heating, would this be enough to significantly lower, or possibly replace, an oil boiler for heat and hot water?

Quick cal: A 5 kw heater, running 12 hours/day for 100 days would use 4,800kwh. Having said that, I would expect more than have of you kwh capacity comes during the non heating season. I would guess it wouldn't be a very good alternative for space heat, except perhaps to supliment. I would think that active or passive solar would be money better spent.

Icarus

BB. · February 2008

Re: Most efficient home heating question?

Dale,

Very roughly, a solar PV panel is around $4-$5 per watt. A solar thermal panel can be down to $0.50 per watt (ignoring installation and support equipment like inverters, pumps, etc.)... Also, a pure solar thermal system will harvest about 3-4x the energy per sq foot (meter) as solar PV panels will (much higher collection efficiency for solar thermal collectors).

So--for pure heating/hot water systems, a solar thermal system will give you a better overall return on your investment. Using solar PV for space heating is a very expensive option (using ground sourced heat pumps for heating/cooling/hot water with solar PV may be a more viable option).

The big issue with solar thermal systems--maintenance. Leaks, rust, failing pumps, compromised panels, how to manage freezing temperatures, heat storage devices, etc., do force second thoughts about solar thermal systems.

SecretsKept,

My two cents on thermal mass for walls and rooms... Works well if you have "raw" solar energy available. Absorb's excess energy during the day (and in many homes, helps keeps rooms from overheating) and slowly releases heat at night.

If, however, you have otherways of storing the energy (water storage tanks, electrical storage/net metering) where you can get "heat" or "cooling" on demand, I may be more interested in the pure insulation only solution (ignoring structural issues).

One problem that I have seen with thermal mass of any type is that, in the end, it usually attracts moisture and eventually mildews/mold (because of wide temperature swings and high humidity)--especially in today's well sealed homes. If you do use a solar mass (such as in an insulated wall), I would make sure that a good vapor to prevent mold/dry rot in the interior walls/structures.

I would start reading "Home Power Magazine" very closely (and their back issues) to see how various people have solved problems in climates similar to your own.

From what little I have read, one of the most common "rookie" mistakes for solar homes is too many south facing windows (and/or too many windows in total). Hard to reduce heat gain during the day and too much heat loss at night.

-Bill

System2 · February 2008

Re: Most efficient home heating question?

BB, again your input was just what i was looking for, thanks for your information and i will be sure to check out that magazine reference!

regardless i still had a bit of trouble understanding totally thermal mass, and i wiki'd it and it helped me understand it a bit but im not fully understanding how directly that relates from 2 products we'll use as examples in this little post:

RASTRA (from what i understand) has little thermal mass because it cannot absorb heat from the inside of the home and release it back during the night (when heating is needed more)

dry block (again as best i understood) has better thermal mass because if insulated on the exterior side and not on the inside will absorb heat from the home and release it back in however in that process also absorbs moisture thus causing mildew...

However if i use something like a solar shed and make it store hot water that can be my thermal mass in the night time instead of really needing the thermal mass from the dry block and with my water based heating system can distribute that heat as needed.

i guess that sounds like its supposed to lol, but really what im getting at is this: would having thermal mass in both the stored water and in the dry block i would build the home from effect me negatively, or is too much thermal mass a bad thing =P i know it causes heating and cooling of a given room to take longer but if i am living in this home as the seasons change and not just on the weekends do you think it would really even matter?

sorry if i seem like im needing my hand held here, this is my first, last and only project im planning literally from the ground up and i'll be living in it for the rest of my life, making mistakes means i gotta live with em and that just adds insult to injury =P

Last thing i asked in the previous post if anyone still has a decent answer, if i use a ICF like RASTRA to build a "pen" in the solar shed to store large quantities of water for heating purposes do you think ICF is the best choice or just exterior insulated dry block, i know ICF's are expensive but im good for it.

THANKS again for everyones info, you've all been really helpful and informative.

mike95490 · February 2008

Re: Most efficient home heating question?

dale wrote: »

I was playing with some numbers. A 9.6Kw system in my area should produce about 12,622 KwHrs of electric per year. If half to two thirds was available for heating, would this be enough to significantly lower, or possibly replace, an oil boiler for heat and hot water?

Why ?

Why use solar PV, at $5w, when you can get solar heat for $2 watt, and less roof space ?

Solar hot water is way cheaper than PV electric

Telco · February 2008

Re: Most efficient home heating question?

I don't think it will matter much either way, since you plan to live there year-round. The only real disadvantage to the larger thermal mass is, if you decide you want it 5 degrees warmer, it'll take a long time to make that temp adjustment. On the other hand, once you get the temp perfect, the thermal mass will resist that change, even if you have to leave the door open for a long time. For example, I've had a roast in the oven burn in the winter before, had to open all the windows to get the smoke out. It was FREEZING in that house in short order. Course the heater was able to get the temp back up fairly quickly, but had I been in a high thermal mass house them temp wouldn't have wavered much with the windows open for the short amount of time it took to clear the air. Wish I'd have had an attic fan, the smoke would have lasted about 5 minutes.

On the expense, I think that the dry stack is going to be a little cheaper. Both will have to have additional insulation added, the Rastra just won't need quite as much. But then, the dry stack blocks will be a lot cheaper than the difference in insulation. I figured that it would cost about 5 grand to put blue styrofoam around my 20x30 garage to get it to an R40, which is a 6 inch thickness. Went with this as I can't get a good on-line price for spray-in foam. The closest I came to an estimate of spray foam was 10 bucks per square foot, and this price included a brick veneer application. Both the dry stack and Rastra will require cement fill and rebar so that's pretty much a wash.

So, I think the main difference between the two is going to be, do you want to be able to adjust temp quickly, or have the temp maintained longer with no energy added.

On the mold, any house has to be controlled for mold. I intend to have an HVAC that actively monitors and maintains a set humidity level in the house. The wife has sinus/allergy issues, so this is a requirement regardless of what we build.

sawmill · February 2008

Re: Most efficient home heating question?

I have been very pleased with our newly installed solar radiant floor system.

This was installed not as a primary heat source but an attempt to reduce heating costs on sunny cold days. We installed 3 pex loops under half of our house which is the primary living area for winter time.

When both pumps are running-takes 150 watts, after solar water panels shut down in the afternoon the floor cir pump(60watts) continues to operate until the storage tank has cooled below useful heat being delievered to floor.

I have found that 100 degree water and up(under the floor) makes a big difference in comfort and reducing other heating costs.

Radiant floor heat can be easily installed in new construction with very moderate costs, if you have interest in this type of heat don't make my mistake of retro-fitting later, much more labor intensive.

paulstamser · February 2008

Re: Most efficient home heating question?

SecretsKept wrote: »

....wood will likely be it although i know wood is not really that much better considernig the impact taking from the enviroment has, my hopes are that i can plan solar heating and space heat efficiency well enough that any outside heating sources like woodburning will be minimal.

If anyone has any other thoughts PLEASE share them, i'd love to find a better solution!

IMO you can't go wrong with wood, esp. if you are cutting and managing your own woodlot. If you do it right, you can actually improve your woodlot for wildlife, habitat, and aesthetics thru selective cutting which can make up in small part for the lack of forest fires in today's Smoky Bear environment.

I have been cutting firewood (and a little lumber) off my 30 acres for 28 years now and managing for wildlife and old growth red pine forest. The real negative impact on the environment here are the infernal deer that knaw and destroy everything on the forest floor and except for a short hunting season, are totally protected and priviledged charactars for the rest of the time. My chainsaw has a MUCH lighter footprint in the woods than does Bambi -- by far!

IMO, PV and wood heat (for cooking & space & water) are a PERFECT combination.

System2 · February 2008

Re: Most efficient home heating question?

points taken guys, thanks for the input, needless to say i think im ready to continue on my autocad drawings, you've all been so helpful, always good to see a good online community of people willing to be helpful and informative so selflessly.

regardless i think i will still plan to use minimal wood cutting, (atleast till my son gets old enough to cut the wood

)

autoxsteve · February 2008

Re: Most efficient home heating question?

share pics of your dwgs when you can. We're interested...

dale · February 2008

Re: Most efficient home heating question?

Icarus, BB, Mike,
Thanks. My windows were replaced this year and storm doors were added. It made a difference, but one room, with very large windows, gets a draft. It is over an unheated, but insulated, space. I'm going to be adding a lot of insulation in my attic and (hopefully) on the ground floor exterior walls.

The system size will depend on the rebates approved and finances when approved. The rebates and solar credits make this a consideration.

The NE seems to pay more for everything and heating oil is/was the highest in the nation. I've heard excess electric can be banked, but provides an much lower amount if sold back. Consequently, electric usage for HW, radiant heat, in this instance could become more attractive.

BB. · February 2008

Re: Most efficient home heating question?

You really have to look at the "Net Metering" and "Time Of Use" metering plans available for your area...

In California, we have a very "progressive" set of rates, Net Metering, and Time of Use plans (in every sense of the word)...

Basically, if you can get your power usage down to some low number (in our area, around 300 kWhrs per month or less), you have a pretty low (for California) power rate... Right now, around $0.12 per kWhr (flat rate) or $0.09 for off-peak rates. Also, Net Metering is a flat ~$6.00 per month charge (includes ~60 kWhrs or so minimum), and any excess power you generate turns the meter backwards and banks retail rate money... If you use more power, you draw from the bank at the same retail rate. At the end of one year, you either pay the extra amount of power you have used, or the excess power generated is zeroed out and you start over again.

The killer is as you use more power, the rates go up... Over ~1,000 kWhr / month, we pay between $0.30 and $0.50 per kWhr (depending on season, plan, and particular rate tier structure)... Typically, our power increases have been aimed at those paying for more than 300 kWhrs per month.

So, for us, if you use a lot of power, even a partial Solar Grid Tied system can offset some pretty high rates ($0.30+ per kWhr). Very useful if you have A/C or electric heat... You do not need to get your whole electric power offset to zero--just get your bill into the lower rate plans.

-Bill

icarus · February 2008

Re: Most efficient home heating question?

If you have large areas of glass, and get drafts, consider (even for all window) some sort of insulated night shades. Many people don't realize that even good double glazed windows are ~r2.5! And that is on a calm day, add a outside wind or an inside draft and the r-value drops. Consider that a 2x6 framed wall is ~r20, ceilings ~r-40, it doesn't take a genius to realize the amount of btu's being lost out the glass. Window quilts, pop in panels of fabric covered styrofoam, even heavy drapes can have a dramatic impact on btu loss in any structure.

Icarus

PS Also works in hot climes in the summer, put them in during the day, out at night. Even in windows that don't get direct sun.

dale · February 2008

Re: Most efficient home heating question?

Icarus, BB,
Thanks. The curtains are an excellent idea. I've also considered adding a storm window outside the center fixed plane window.

Thanks again,
Dale

Mangas · February 2008

Re: Most efficient home heating question?

You're getting some great navigation.

In my case, I used Rastra construction, Anderson triple pane windows and have retractable steel shutters on all windows and doors to selectively control the sun on the house or, close it up when I'm gone for thermal efficiency/management.

Since the liveable portion of the house is 3,500 sq. ft, I am running central A/C and Heat.

Most efficient home heating question?

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