The largest energy consumer of any home-built in the northern hemisphere is the heating system.
Designing the correct heating system is critical in the success of the off grid home.
Build it wrong and nothing else will matter. Almost all heating systems require some form of electricity to operate whether it for the fans (oil, wood or gas hot air furnace), circulating pumps (oil, wood or gas boiler), thermostatic and safety controls (almost every system) or auger (wood pellet stove). The worst part is this extra electricity is needed most when the days are the shortest and the sunshine is scarce. Check out our favorite heating system.
Heating systems in “off the power grid” homes are often the weak link in the system. The conventional “plumbing and heating” installer will insist there is only one way of doing things and try to force you into following the building codes.
Unfortunately the building codes are often outdated, unrealistic and will not work for the solar-powered home.
First, there are a few heating options that are NOT AVAILABLE for the off grid home.
- Electric Heat
- Oil Furnace/Boiler
- Heat Pump/Geothermal
The above heating methods are out of reach for 99% of those deciding to live off of the grid. They require far too much electricity.
Using electric space heaters, baseboard heaters, boilers and/or low wattage under floor radiant heating systems consume HUGE amounts of electricity. Any heating load, whether an electric heater, a hot water heater or electric range, is too large to even consider for all but a few off the grid homes.
If you are planning on making your own electricity using solar panels, wind turbines or a gas/diesel generator it is impossible to make enough electricity to power heat loads (resistive loads). There may be times when you have enough electricity to operate a heater as in a dump load but the extra power is usually in the summer.
The one exception is the home owner fortunate enough to have a massive resource of falling water. A micro hydro powered home might be able to operate some electric heat as a dump load but it is very rare.
Although heating oil is the primary source of heat in the above heating systems there are also some large electrical requirements as well. Oil burners use high pressure pumps to force the oil through a fine nozzle to vaporize the oil enough to burn efficiently.
They also use electricity to ignite the fuel and a fan to make a clean and aggressive flame. In addition to the boiler, there is either a large fan (furnace) or circulating pumps and zone valves (boiler) to move the heat where it is most needed.
Last but not least, is the thermostatic and safety controls which are usually operated with transformers that consume energy 24 hours per day. Anything that uses electricity 24 hours is of particular concern for the solar home. Some solar power systems are designed to sleep at night in an attempt to conserve electricity until it is required, as in the case of a light being turned on or the refrigerator compressor starting.
The thermostatic controls/safety controls will keep the system awake at night (phantom load) draining the batteries/battery bank.
Although geothermal heating systems are very efficient by today’s standards, they are not suitable for the typical off grid home. A good heat pump system will consume about 1/3 the electricity an electric heater will use.
A small well insulated home might use 1500-2000 kWh per month just for electric heat. To heat that same home with geothermal, 500-667 kWh will need to be generated per month. If your electricity is produced with solar modules you would need to purchase another 16000-22000 watts of solar ($16,000-$22,000) and up to 52 more batteries (Trojan L16 – $15,600)) just to run the heat pump system. These numbers are based on getting 1 sun hour per day in December and January. It is just not affordable for the average homesteader. Just like electric heat, you might be able to operate a heat pump with a large water turbine. For the rest of us, we will need a less electricity dependent heating system.
UPDATE AUGUST 2015: As solar modules are getting less expensive and some homes are super insulated it is possible to heat your home with a heat pump. It will still cost a lot up front but it is possible for some.
What are the good choices for heating a solar home?
As our electricity consumption needs to be as low as possible, we will need to do things differently than our neighbors. Even something as insignificant as a circulating pump and some zone valves can use more electricity than we can spare.
The most obvious options are:
Solar Hot Water
At first it might seem like solar hot water is the obvious choice for heating your renewable energy home.
It is green, renewable and downright sexy but also very expensive, high maintenance and complicated. It is one thing to install a photovoltaic module, run some wire and connect to a charge controller. It is a whole different process for solar heating. Solar hot water collectors are often heavy, fragile and cumbersome to mount. Installing the plumbing, controls, heat exchangers, hot water storage tanks, pumps and thermostats is beyond the scope of the average homesteader. Not to say it can’t be done. It is just more than the average do-it-yourself homesteader will be ready for.
There are also major considerations such as:
- How many sun hours will I get per day in the middle of winter?
- How large of a storage tank will I require?
- Will I need to use a double wall heat exchanger or will a single wall meet code approval?
- How many collectors will I require?
- How will I keep the heat transfer fluid from freezing?
- Should I design a closed loop, open loo, drain-back, direct or indirect system?
- What will I do if the sun doesn’t shine for a a day, a week, two weeks?
- What am I going to do with the abundance of hot water I generate in the summer?
The biggest problem with a solar hot water heating system that it is required the most when it is able to produce the least.
In the middle of January, the sun rarely shines while it is one of the coldest months of the year. In the east coast of Canada we average 1 sun hour per day in late December and early January.
Undoubtedly you will need some type of ‘backup heating system for those cloudy days or very short days. Even though it is possible to design a solar hot water heating system that will work flawlessly and completely, it would be unwise to not incorporate some type of backup system. More about solar hot water to come later.
UPDATE AUGUST 2015: I have seen a few solar hot water systems that were able to provide 100% of the heat for large homes in the New England States as well as in Canada. Each of these systems cost well over $100,000 and were massive, containing up to 20 hot water collectors and storage tanks as large as 1600 gallons(6000 liters). One in particular has been operating for over ten years and the water in the storage tank (according to the owner) has never gone below 190 degrees F (88 degrees C). Pretty impressive but out of reach for me and most other homesteaders.
Burning wood is by far the most common heating method for the solar homesteader. Wood is hard work and dirty but most folks who decide to live off the grid are not deterred by a little work and dirt.
The simplest wood heating system with the lowest electricity requirement is the common wood stove. The majority of wood stoves operate with no electricity or fancy controls making them ideal for renewable energy homes. However they might not be the best choice as they only heat a small area, can be very inefficient and require the addition of firewood constantly.
Other options include the wood hot air furnace (fan uses a huge amount of electricity), indoor and outdoor wood boiler (go here for efficient circulating pump setup), pellet stove (auger and fan consume a lot of electricity) and rocket stove/rocket mass heater (impossible to get building code approval).
The beauty of gas is the ease of handling and the ability to store massive amounts on your property with little effort. If you are living off the grid, you will likely use gas for cooking and/or hot water. Adding a propane/natural gas heating system is the logical next step. There is a lot of variety when looking for a gas heating system. Some are good, while some are horribly inefficient.
If you go to your local home improvement store and buy the cheapest propane heater you can get you should expect an efficiency of about 50%. For every liter of propane you purchase and consume, one half goes into home heating and the other half goes out the chimney.
The better option is purchasing a high end propane boiler/water heater like the Polaris made by American Water Heaters, USA. It boasts an efficiency of 96%.
You can quickly assess the efficiency of a gas heater by looking at the chimney or venting system. If the gas heater requires a steel vent or full blown chimney, you can expect it to waste a lot of propane/natural gas. If it is vented by a small plastic (ABS or PVC) vent you can be pretty sure it will be efficient. Less heat going out the vent means more heat in your home.
Propane/Natural gas heating systems can be hot water boilers(like the Polaris) , hot air furnaces (van uses a lot of power), water heaters, vented space heaters, fireplaces and non vented space heaters (most require no electricity and are 100% efficient). The efficiencies can vary widely between any of the above heaters except the non vented space heater. As it is non vented, all of the heat stays in your home making it as close to 100% efficient as possible. Check out the different propane/natural gas heating systems before making a decision.
Pellet stoves are not often talked about but they do have their place in the off grid home. They are very reliable, a lot cleaner than firewood, fairly efficient and able to be operate for long periods of time between fill ups. One of the problems with the pellet stove in the off grid home is the amount of electricity required for operation. The auger, ignition system and fan all use electricity. You must get all the details before purchasing your pellet stove. Some do not require much electricity and can operate in the event of a power outage. Some use a huge amount of electricity as their glow plug ignition system operates constantly using up to 1000 watts the whole the unit is operating.
Most wood pellet stoves take inside air for combustion of the pellets. This can be a problem as it is taking warm air from your home and dumping it outside. The air removed will be replaced with cold outside air making your home harder to heat. In a small, tight home (like an energy efficient off grid home) this can rob your home of oxygen. Fortunately you can get a pellet stove such as a Harman that uses outside air for combustion.
There is even a wood pellet stove (Harman PC45) that can burn many fuels including wheat, corn, cherry pits, sunflower seeds and others. Choosing the best wood pellet stove for your solar home can be a challenge.
Contact a reputable dealer and get a spec sheet before you make any decisions. You can even call the manufacturer to get the power requirements while the unit is operating and while it sits dormant. Some pellet stoves are a phantom load.
As off grid homesteaders we always need to think outside the box. We cannot waste energy like our neighbors. It is too precious and too expensive to make our decisions lightly.
Biomass might be an option when designing your solar/off the grid home. It is relatively new and mostly misunderstood. The term biomass heating refers to generating heat from living organisms. Most of the time the living organisms are plant based as in wood chips, compost, corn, grains etc. However some biomass energy might be gathered from animals as in the collection of methane from cows. Sounds easier than it is!
Some of the simplest biomass heating systems are nothing more than a pile of manure, leaves, sawdust and small sticks with multiple coils of pipe inside use to heat water or a pile of compost inside a green house constantly generating heat.
We are in the research and testing phase for a few types of biomass heating systems. As we get more facts and prove more concepts we will update our biomass home heating page.
Hybrid Generator Systems
The last form of heating system we will mention here is the hybrid generator heating system. Most of us will need to rely on a generator for electricity production at some point in time. Some of us have long periods without sun or very short days in the winter. A generator is just a fact of off grid life. One of the problems with a combustion engine generator is the poor efficiency. A large amount of fuel is consumed to make a small amount of electricity. In fact most of the fuel is turned into heat instead of electricity. A hybrid generator system captures that lost heat and uses it to heat your home.
The most common method of capturing the heat is by rerouting the cooling system from the radiator to a heat exchanger like the one shown above, and from the heat exchanger to your home. The other method of heat capturing is by making a heat exchanger for your exhaust pipe and directing that heat into your home. The above heat exchanger would work for exhaust as well. Some systems do both.
We have seen homes that are making up to 50% of their home heating by simply recovering the heat from the fossil fueled generator. It makes sense and is not that hard to setup.