Tiny House Hot Water: On-demand propane water heaters and important lessons learned
I've talked about options for doing laundry in a tiny house, but what about some of the even more basic needs? For most of us (unless you are really roughing it), hot water is something very important. Many people don't know what the best options are. Here's my opinion...
Benefits of a propane on-demand water heater
When it comes to hot water in a tiny house, I'm convinced that a tankless, on-demand system is the best option. There are electric tankless heaters and propane/natural gas heaters. Both are great. Electric models tend to be a bit cheaper, but any electric heating elements will use a lot of power. Since many tiny housers are thinking to live off-grid (or might want that option in the future) or are just more conscious of their overall energy use, I believe a propane tankless heater is the way to go. Here's why:
- On-demand heaters offer a limitless supply of hot water
- Propane is relatively cheap and reliable for on- or off-grid living
- Tankless propane heaters only heat water when needed - they do not use energy keeping water hot in a tank
- High efficiency units can heat a lot of water with very little propane cost
Things to research about each model you are considering:
- BTU output or max GPM flow rate at certain water temps - make sure the output matches your needs
- Minimum GPM activation rate and min flow rate to remain activated (lower is better for hot water even when a tap is not turned all the way on)
- Size, installation/clearance and venting requirements
- Freeze protection built-in?
Beware of Freezing Temps!
On-demand propane heaters come in two varieties: Those meant for indoor installation and those meant to be installed outdoors.
Though outdoor units are easier to install because they do not require the same venting (indoor units must pull fresh air in from the outside and vent out combusted propane gasses), they can also create some problems, most notably freezing. Everyone's climate is different, but if in winter it gets below freezing in your neck of the woods, then think carefully about how to protect your heater from damage when water freezes. In addition to the water coming in and out of the heater from your supply lines, hot water heaters can also collect condensation, which can drip down into the unit, and then freeze, causing damage to the propane heating mechanism. I've heard stories of people's water heaters breaking in the first hard freeze and then them not having hot water for a good part of the winter.
For this reason, I think most tiny house builders should consider an indoor unit (vented properly, of course). This way, the entire unit, including water supply lines, can be included within the insulated portion of house, preventing it from freezing in all but the most frigid temperatures.
Residential vs. RV units
In addition to indoor/outdoor options, there are also Residential units and those designed specifically for RVs. More options exist in the residential market, with some being cheaper, but use caution here as well. Some water heater manufacturers do not consider installation in a tiny house as acceptable use of the product, and may not honor their warranty or offer any kind of support or service (read below for the lesson we learned the hard way).
Here's a rundown of some of the more popular options (both residential and RV).
Lower output suitable for hot water for one appliance use at a time. Cheaper, but with more plastic materials used.
Higher output than above model, suitable for small family home or multiple hot water uses at the same time.
Takagi T-KJr2 (website)
High output suitable for small family home. 80+% efficiency.
Rheem/Richmond RTG-64 (website)
High output suitable for small family home. Very low 0.40 gpm minimum activation flow rate. 80+% efficiency. Freeze protection.
Editor's Note: We chose this model. I did not know this when purchasing, but Rheem's installation guidelines specifically state that the product is not intended for RV or mobile home use -- they will not honor the warranty (more on this in a future blog post). This is likely the case for all residential models, with the possible exception of those from Eccotemp, who is more tiny house friendly (based on the anecdotes I've heard).
Thanks to Sean David Burke for finding this great alternative. While listed under the residential category, this unit is also "Certified for Installation in Manufactured (Mobile) Homes," so can be used in a tiny home without voiding the warranty.
Very similar specs to the Rheem unit above: high output suitable for small family home. Very low 0.40 gpm minimum activation flow rate. 80+% efficiency. Leak detection w/shutoff.
These heaters are designed for RV or "mobile home" use. Typically these units are more compact and are installed in the wall cavity itself. This means they are more of an indoor/outdoor type, without the need for venting, but more exposed to the cold. Some include freeze protection features. These units will create more thermal bridging as the section of wall where installed will not be well insulated.
Cheaper price tag, but lower 36,000 BTU output. Requires min 1.o gpm flow rate for activation.
Highest price tag for highest 55,000 BTU output.