Bad news: heating is expensive. GOOD news: well-made tiny houses use so little! Bad news: builders making units like “Park Models”, still think that just because it’s tiny and uses less, there is no need to beef up insulation or make more efficient heating. GOOD news: we have choices to both beef up insulation and decrease the heating footprint.
It is helpful to put your choices for insulation and heating in the framework of the size and configuration of your tiny house. You may find that, as nice as radiant floors are, the better option may still be one of the tiny, fuel burning, wall mounted heaters, or even a free-standing electric “oil filled radiator” type unit that can be stored out-of-season. Whatever you do, maximize your insulation; it is your first line of defense against extreme temps!
The average adult human emits about 100 watts of heat. Compare that to having a 100-watt incandescent light bulb burning in that space [and it gives light, too]; in a very tiny space, you could simply run a couple 100 watt bulbs. But, incandescent bulbs are now ‘dinosaurs’, leaving you inside your unit, as well as whatever other appliances or pets that emit heat: you might need a bit more to stay toasty!
No matter what the heat source, if the place lacks maximum insulation, you will pay to heat the great outdoors: might as well be sitting around a campfire in some buildings. Insulation can be tricky to figure; some builders have gotten creative by hybridizing various types of insulation; some of those schemes will be haunting them later!
A few factors must be respected, about insulation:
-The “R-value” measurement does not apply equally, nor the same, to all types of insulation materials.
-There is a dew-point somewhere inside the wall, to be considered.
-Perceived warmth is first from radiant, then from convected, lastly from blown; which coincidentally, also matches their efficiency: you will pay for least energy to make radiant heat, then convected, most energy to make blown–blown heat is most costly [yet perversely, most often used in all buildings!].
Radiant floors are so nice! These heat from the ground, up, no stratification of temps in the room. It hides in plain sight, they are clean, no dust created or blown, no fumes or ash products to haul out, no burn-chamber to clean out.
These only need kept at about 65 degrees, year-around, creating stable temps indoors. If used in elder housing, it can be warmed up to about 75 or 80 easily enough. Radiant floors come as electric matts made to fit your space, or fluid-filled tubing with a heat source.
If your tiny home is Grid-connect capable, you might more easily use electric, instead of water/fluid-based systems that use precious square footage to house the heating equipment. If your tiny home stays put and has room for the heating equipment, a fluid filled system may be just the ticket. Electric radiant heat is not generally used for off-Grid systems, as those usually lack “heating quantities” of energy.
One drawback to all radiant-floor heating systems is that some folks are sensitive to the subtle-energy moving under the floor [refer to studies of, and reference pages about, Baubiology]. Whichever type system, the entire building envelope needs very well insulated, so the heat you pay to create stays inside your tiny home.
Radiant floors are best under open areas of flooring, not under beds, walls, cupboards; it’s fine inside closets, to help prevent moisture build-up in closets [therefore inhibiting mold]. It is important to use good quality components, well installed. It is great if the system is easily fixed, and lasts a long time. If the radiant floor is under standardly installed tiles or wood, repairs can be costly, time-consuming and messy. If the floor equipment is installed under removable hard-surface floor-sections, it’s pretty easy to fix, if needed.
The usual fluid-filled system uses ½” PEX-type tubing rated for hot water [it all is, however some is tinted red and has oxygen barrier], a pump to move fluid, and possibly a manifold for ease of maintenance and directing flow. For just one room, there is a single in and a single out pipe, hooked to a heat source. It needs a fill/stand/burp pipe, and a well-insulated spot to locate the heat source. Thermostats set/control desired temps.
The fluid can be simple 50:50 distilled water:glycerin [veggie glycerin does not freeze], or other commercial non-toxic formula. On-demand hot water heaters are spendier than tank-hot water heaters, however those gas models use markedly less fuel and can have capacity to feed two loops: one for your household hot water, one for your floor. For tiny houses, though, you might just use plain water from oyur source, and get your heated water via the floor loop~you just will not get very hot water from that.
Tankless can be gotten for outside with weatherproof-mounting: a plus for a tiny house. A 10 or 20 gallon tank hot water heater costs nearly as much as a 40-gallon model, and takes up lots of room, yet sometimes, is the best solution.
IF you have enough sun to heat hot water even in winter, you could place a 4’x8’ water-heat panel on your roof, however that will not heat during the night unless you get complicated and bulky. The cost for an entire average hydronic heating system ranges between $6 and $12 per square foot, two to three times the cost of other heating systems. However, a hydronic radiant system offers substantial operational savings. At tiny-house scale, you can save around one-third over what you’d pay to heat by forced air. The price drops if you DIY it. It can be tiled permanently in place, or you can locate hard-surface floor sections to set over the floor components, easing future access, and allowing easy change of floor covering.
-The key with flooring is to protect the tubing or cables from friction or pressure points.
Fluid-filled tubes are versatile, in that these can use any kind of heat source that warms the fluid. Small hot water tanks, on-demand water heaters, solar water heat panels, loops through a woodstove–each of those are an option.
Even geothermal loops in the ground to keep the floor at the earths mean-temperature [about 55 F.] with a simple solar-run pump, might be considered [which also provides cooling in summer].
Electric matts are simpler and less costly [well, up-front–you pay for electricity ever after]. It is said that electric radiant systems do not replace the main heating system, just augment it. However depending on your climate, size of tiny house, size of system, and your own preferences, it might be all you need. It needs to be plugged into the Grid [electric “mains”].
It needs a dedicated 15- to 20-amp GFCI-protected circuit to power the system. An average bathroom-size warm-floor retrofit will cost $400 to $700 including the cost of the usual new tile floor. This system will use about 300 watts.
For a tiny house, you can use multiple of these if necessary. Electric matts are ordered to fit your space. Some come in small sections that can be plugged together–these need carefully arranged or trimmed so as to avoid cutting the cables.
Keeping your whole electric heat system to about 600 to 800 watts, means you will also be keeping your electric bill about $30 to $50 per month LESS than if you use any system that runs on 1500 watts while it is on. [We’ve been using one heater run on 600 watts, even in 20 F winter weather, to keep our tiny house [about 800 s.f.] nicely warm. If outside drops into the teens for temps, we have occasionally cranked it up to 900 watts until it returns to the 20’s.]
Googling for “radiant floor heat kits” can find lists of those who use your floor’s measurements and layout, to put together easy-to-use kits [well, easy for the already DIY-handy!].
Depending on location, one may or not be wise in hiring it done by someone. For instance, if plumbers in your area are only used to installing regular pipes, and never done a radiant floor, I would be leery of letting them do my radiant floor: those tend to be stuck in their familiar patterns and knowledge, less able to make the changes that work best with PEX, for instance.
Keep the number of the company that sent the kit handy; make sure it’s a weekday to facilitate reaching them; read your directions thoroughly, first; get any questions answered before you start, and figure there may be more questions as you work on it…and you may need to fetch more parts from the local hardware store: make sure there is source for more parts within driving distance!