Tiny Home Heating Options Part 3
Part 3: Heat Distribution, Air Quality, Safety, and Sizing
If you haven't already read part 1 or 2 of this post, you can start here.
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In a small enough space, heat distribution isn't an issue. But small long and skinny spaces or spaces with multiple rooms might need some extra help to provide even heating. And if you're using a hydronic heater, you'll need some kind of radiator to get the heat into your space.
Many RV air conditioners are designed to work with ducting, and RV propane furnaces use ducting to distribute heat both to the living space and to the water tanks. But even if your heat source doesn't use ducting, you can add it yourself.
There are some nice 120V fan systems available that mate with 4" dryer vent and even air filters. You can hide the duct inside of a cabinet to run air from the warm area of your house to a colder area. Wire it with a thermostat in the cold area for a fully automated system. If you're using a 12 volt house battery and you don't mind tinkering a bit, it might be worthwhile to use a 12 volt computer case fan with 3" dryer vent and a 12 volt thermostat instead.
Hydronic Heat Distribution
If you're using a hydronic heating system, you'll need some sort of radiator to distribute the heat into your space. The heating loop should be filled with glycol to prevent freeze damage to your equipment. The glycol loop needs a small expansion tank to allow for thermal expansion of the fluid, and a pressure relief valve for safety. Some hydronic heating systems can work passively by convection, but some need a circulating pump if one isn't included in the heater already. You can use a purpose-built household recirculation pump for a 120 volt system, or use a 12v hot water pump for a 12v DC system.
If you're interested in doing some tinkering, it should be possible to drive a 12 volt water pump using a few thermoelectric modules driven by the heat source. This would be a great project for an off-grid wood stove feeding a hydronic heat loop.
In-Floor Hydronic Heat
My favorite type of hydronic heat is in-floor radiant heat. The principle is the same as electric in-floor heat, but instead of an electric coil, you either sandwich a PEX coil between the finished flooring and subfloor, or mount the PEX coil to the underside of the subfloor with a heat transfer plate, then insulate below.
Natural convection won't adequately circulate glycol through a hydronic in-floor heat system, so you'll need a pump if your heating appliance doesn't already have one.
Modern designer radiators are available in more traditional or transitional horizontal designs, or modern, tall, short vertical or horizontal designs. Towel warming radiators are available for bathrooms in modern or transitional styles.
Indoor Air Quality
Indoor air quality is a concern in any space, but it can be an especially difficult challenge in small spaces during the Winter. Dust, humidity, VOCs (volatile organic compounds, i.e. nasty man-made chemicals), and mold spores tend to build up very quickly in small spaces. Mold spores in particular can be exacerbated by added moisture from appliances that produce water vapor like unvented propane, butane, or ethanol heaters or cooking appliances. Building a relatively airtight space can be great for energy efficiency, but it can also make for an unhealthy environment.
Air filtration using a HEPA filter (like this one that can use a 12V power supply) can vastly improve air quality in small spaces by removing particles. If the filter is equipped with a carbon filter, it can also remove VOCs from the air.
The best way to maintain good indoor air quality is by regularly exchanging indoor air with the outside air. Opening windows or allowing drafts isn't the most energy efficient strategy for exchanging air in the winter. A heat recovery ventilator (HRV) can be used to exchange indoor air with outdoor air while keeping heat in the building. An HRV is a counter-current heat exchanger that transfers the heat from exhaust air into the fresh air intake, returning the heat to the building while exhausting the (now cold) inside air.
Safety is a critical consideration for any heating system. If a particular heating option cannot be used safely in your space according to the manufacturer's instructions, you should choose a different heating option.
Tiny homes are typically not subject to building codes, but that does not mean you can ignore them. Safety requirements are there to protect your life, the lives of your family members, guests, and the lives of first responders. The best way to avoid burning down your house is to follow the manufacturer's instructions for installation and clearances.
For electric heat, make sure your wiring is rated for the load of your heater plus anything else on that circuit. You should try not to rely solely on a safety device like a breaker or a fuse to avoid burning your house down. Know the rating of your circuit and the load of the devices on that circuit, and don't exceed the rating. If you're using an extension cord to hook your house up to a generator or shore power, make sure the cord is rated for the total electrical load of every device running in your house. An electrical protection system like the Progressive Dynamics EMS is cheap insurance for protecting your home, appliances, and life, on top of the usual safeguards like circuit breakers, fuses, and using your head.
Most heating devices have requirements for clearance from combustibles. Know how far a heater or radiator must be from combustible materials like upholstery, curtains, sheetrock, and wood, and don't violate those clearances. Most commercially available heating systems are very safe if used properly, but homes burn to the ground every day with and without families and pets inside of them because of simple clearance violations.
Always maintain at least one smoke alarm and one CO alarm in your living space. Modern smoke and CO alarms are available with batteries that last the full lifetime of the alarm. Smoke alarms should be positioned high on a wall or on the ceiling near the sleeping area. CO mixes freely with air (it doesn't sink), and detectors often have a screen with a CO level reading. So, the best places for CO alarms are on the wall somewhere that they're easy to read, preferably near sleeping areas. Keep alarms away from heating or cooking appliances to avoid false alarms.
Propane tends to sink and pool in low areas, so if you use propane in your house, you should have an LP alarm in your living space, located near the floor. LP alarms are available using AC adapters or 12 volt DC. You will most likely smell gas before the alarm detects it, but an alarm can save your life or home if you're sleeping, in a loft area, or if a neighbor hears the alarm while you're away.
Sizing Your Heater
Some manufacturers like to claim that their product is suitable to heat up to a certain square footage. But there's a lot more that goes into heating than the size of the heater. How well insulated is the space? Are the doors and windows tightly sealed, or are they leaky? What's the temperature outside? What temperature do you want it to be inside? Don't take the manufacturer's square footage number for granted.
The only way to know how much heat you need is to do some math. Find a few online BTU calculators, plug your space in, and play with the numbers. There's a little guesswork involved in things like the insulation variable and the climate, so check a few different calculators before you settle on your numbers.
Look up the BTU rating of the appliance, and compare it to the needs of your space. Talk to the manufacturer of your primary heat source, and see if they agree with your numbers. While you're at it, how responsive are they to your questions? Do you get the feeling that they'll help you out if you have trouble with the install or need warranty repair? Do they have any promotions or coupon codes available?
Remember, you don't have to choose just one heating method. For cold climates, a combination of heating methods might be the safest bet. You might choose a propane hydronic heater for domestic hot water and in-floor heat, and add a propane furnace to keep your space toasty on the colder Winter days. You might use a mini-split electric heat pump for primary heat, but add a small wood stove for ambiance and backup heat for when the power goes out.
Bigger is not always better. A forced air system that's too large won't be able to cycle through the air in your house before the thermostat turns off, resulting in hot and cold spots in your home and high energy bills. A wood stove that is too big can be difficult to keep under control, either making you open your windows in the middle of winter to cool your space down, or having to choke down the fire and fill your chimney with creosote, risking a chimney fire. The best heating system is one that precisely fits your needs and your space.
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