How-To choose a hot water heater for your Tiny House

This morning I awoke only to see the digital thermometer taunting me from its place on the kitchen shelf – 23° outside and 69° inside. Before I even left the warmth of my double down cocoon I could feel my toes pressing against the icy floor. This morning would begin with a shower (I say this only because not everyday begins or even includes such an act) and because of the cold, I was happily anticipating up to 5 minutes of thawing. I lathered the shampoo/bodywash/soap concoction on my head and started working it down when the water began to drop in temperature. This typically doesn’t happen. I asked myself, “Has it been 5 minutes already?” Typically both Crystal and I can take a warm shower one-after-the-other without a loss in heat. “I must have gone overboard with the hot,” I told myself. In the bungalow we have been most satisfied with our choice in hot water heater. An Ariston 4-gallon Electric Hot Water Heater fit our needs and still fits our needs well. And because we are currently tied into the grid we have not regretted our choice for an electric unit. But when considering our options for a hot water heater in our Tiny House we have thought much differently.

A trip to the Interwebs or (and I shutter to say this as gas prices continue to creep up) to the local big box home-improvement store is, well, overwhelming. There are too many brands and too many sizes to choose from. Unites use different fuel sources and display a host of energy ratings. And then you have the tankless units. Where did the tank go? It’s not that overwhelming though if you know your needs, are familiar with your options, understand your fuel possibilities, and have thought about how long you and your families showers actually are.

  • Electric – uses large coils that hang down into the tank to heat the water. The coils are similar to the ones in an electric oven. Generally, electric water heaters aren’t as efficient as those powered by other fuel sources, and electricity is more expensive than natural gas or propane. However, they’re less expensive up front and don’t require venting. If your water demand is small, then it may be a good way to go.
  • Let’s first take a quick look at the fueling options.
  • Natural Gas – This unit uses a gas burner at the bottom of the tank, with a venting chimney that runs through the center and out the top. The carbon dioxide and water vapor byproducts are vented through the chimney and then run outdoors through a chimney or side wall vent. There is a gas pilot light to produce the flame. Natural gas models cost more than electric but are much more efficient.
  • Propane – This unit works in the same way as a natural gas unit except that it uses propane as the fuel source. Propane is generally used as a fuel source when a home doesn’t have access to natural gas. The propane is supplied from a large tank on the property. This is probably the most popular option for tiny housers who intend on “parking” for an extended amount of time.
  • Oil – I have bad dreams of these units due to childhood, hitting my head on a big, ugly tank when going out long for a, um, backyard touchdown pass, and awaking to the smell of a gas station above my head. Similar to gas and propane models this unit mixes the oil with air using a power burner to create a vapor mist, which is then ignited by an electric spark. Like propane, oil heat is typically used when natural gas isn’t available and is also delivered to the location and stored in a large tank. (and usually placed in the most inconvenient place.)
  • Solar – Now we’re talking. A solar unit uses the heat from the sun to produce hot water. The heat is then harvested by an absorber panel that typically sits on the roof. Tubes inside the panel either directly heat the water flowing through them or a transfer fluid that warms a heat exchanger. This exchanger heats your home’s water in a storage tank. Solar systems can be used in conjunction with a conventional system to cut up to 80 percent of your water heating bill. I am not sure about the panel sitting on the roof or even how large the tank is as solar heating is very new to me. However, this video explains a system quite well!
  • Heat Pump – Quite simply, this unit takes heat from the air and delivers it to the water via electricity. Rated at 2 to 3  times more efficient than electric water heaters, consumer demand is low and there are few manufacturers. They cost more up front than conventional units and can only be used in areas where the temperature stays between 40 and 90 degrees year-round.

So far I think it is pretty clear to see that the decision on a hot water heater relies largely on where you “live” and what kind of unit you can support with your structure. If you have access to natural gas, it can be a very fuel efficient way to go. If you park in outlying areas where it isn’t available, then your tiny home is probably going to use oil or propane. Solar heaters are best used in areas where there’s abundant sunshine and while heat pumps can shave a great deal of money from your bill, they are uncommon. ­If you want a cost effective system that’s easy to maintain and service, then a natural gas water heater is probably the way to go.

Hurry up and get to the tankless!

Tankless hot water heaters have become quite the rage recently. They are great for tiny housers as they take up little room. For more traditional homes they currently come with a federal tax rebate and overall are more efficient than storage tank models. Tankless heaters heat water as it flows. No one will run out of hot water as I did just this morning. Tankless heaters also last up to ten years longer than a storage tank. Electric tankless units don’t produce a shred of greenhouse gas and there is no possibility of flooding due to a ruptured tank.

There are some drawbacks though as we have found out. Natural gas whole-house units can cost up to 3 times as much as conventional heaters. We have been looking at Rinnai’s V53i interior-mount tankless water heater but have been somewhat discouraged by its $870 price tag. That simply was not in our initial budget. So while you’ll have an unlimited supply of hot water, there are limits on volume because the output is split between all of your fixtures. Some houses require a larger natural gas line to supply the unit with enough fuel, adding to the price. Further expense comes from venting the gas or propane with pricey stainless steel tubing. If you go with an electric unit (which we haven’t ruled out), it may require an additional power circuit. Gas powered models produce some greenhouse gases and require annual servicing. And lastly, depending on the size of your home, the time that it takes to get the hot water from the heater to your faucet can increase water waste. This is a huge discouragement for us which has prompted us to relocate the hot water heater to inside the bathroom where it will have the least amount of space to travel.

Because I am neither a plumber nor an electrician nor even a hot water heater salesman, I have no real advice as to how to choose the right unit. There are a number of factors to consider between your needs and your desires. It is an important decision though, even for a tiny house.

What are your thoughts? Do you have a tankless? Are you still paying for oil? Do you wish now you had a different system? Please comment and let us know if we should be considering one unit over another. And as always, if you like what you read, share it on Twitter or Facebook with the social media buttons below!


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  1. says

     I really like this post.Actually am reached here by searching aboutyt the heat pumps.Post explain the good ways which are helpful to me for choose a hot water heater for my house.The energy concepts shared in the post is really informative.

  2. K Pence says

    We live off the grid and have a small tankless Bosch I think it’s called a 125 unit. We have three kids, two at home. It’s considered very small for a family but we just are aware of whose in the shower and try to only do dishes if no one is in the shower. I rather like this efficiency.

      We are working towards a solar hot water heater up near our garden, but it seems complex to my husband and I, a very high tank above the hydronic panels, a pressure gauge(? That sometimes fail?) . We will get another Bosch 125 for our outdoor kitchen/shower house for now.


  3. says

    A simple solar water heater can be a large black drum, covered, on a mount over the (outdoor) shower, with reflectors directing sunlight onto it. It is filled with a float system.  The gentleman who built and owned it said he had to be careful, as straight from the tank it was REALLY hot.  As long as it receives several hours sunlight, you have hot – or at least warm- water.

    • anotherkindofdrew says

      I am not sure if you have ever seen but when we lived in Georgia we had an outdoor solar heated shower we used quite often. You can see that archive here:

      As for our everyday living, I don’t think it is truly practical at this point although it is a feasible solution and is used all over the world as the ONLY hot shower method.

  4. says

    I’m a fan of the RV tankless heaters, because they run on DC power and are designed for a mobile home. The only thing you have to look out for is to make sure you get one that can survive in cold temperatures (if you live in that kind of climate)

  5. says

    I run a small Bosch tankless propane heater. It is reliable and even fills the bathtub in my tiny house. It requires no electricity, so it can be used completely off grid.

    Installation is fairly complex, and although this particular unit costs something like $430, expect to spend quite a bit more on pipe fittings, gas vent pipe, roof flashing (if needed,) and the like. There are some RV models that are simpler to install, and have slightly lower output (fine for a sink or a shower.)

    Electric on-demand water heaters SOUND great, until you figure out just how much electricity they draw when on. What this means is that you will need a large feeder circuit, up to 120A at 240v! The wire for this is large and expensive, and I don’t recommend working with circuits like this unless you really know what you are doing. Additionally, you would likely have to install whole new electric panel to achieve this, not an option in a towable tiny house. Large RV hookups are rated 50A at 240v… that is half of what many on-demand electrics need. See what I mean?

    • Andrew Odom says

      WOW! Great information and some specs I was clueless about. Thank you so much for sharing. Feel free to drop tips like that ANYTIME!

    • Magnus says

      RV’s don’t use 240 VAC… with the sole exception of the ultra ‘luxury’ models ($$$,$$$). And their risk of going up in a blaze is greatly increased for it too…. seeing as it’s been done by rigging up two 120V branches from each panel leg and joined up to the dedicated plug (such method doesn’t meet muster of any build code now, BECAUSE of the increased fire risk; even if you do somehow have a 240V breaker behind it, doesn’t matter… the risk is still there, because the PANEL itself doesn’t actually have the hardware/wire gauge that could safely handle a 240V spike back towards itself… which, unfortunately, is an all too potential reality – especially if you’re relying on two breakers on two feed rails to actually trip at the very same instant. It would be a real tear-jerker at best, were that to happen and that breaker – rather, breakers – for whatever reason, fail to trip).

      NEMA 14-50R, for RV use, is actually 50A-+50A @ 120V – the panel is what actually splits the cumulative 100A on it’s two poles or ‘legs’. On the actual service pole, the plug is wired with two 120V, a white wire (constantly alternating the two 120V so the plug is never being fed both at the same instant) and then the green ground. The ones wired for temporary service, as for construction, are two 120V but without the white/alternating wire and the ground (thus, 240V @ 100A service).

      Never, EVER, plug into a NEMA 14-50R pole without first confirming what it’s wired for. Good rule of thumb is that if there’s only three, instead of four, wires DO NOT PLUG YOUR THOW/RV INTO IT! THAT’S 240V!!!

  6. Scott S. says

    One major issue to consider when looking at tankless water heaters is the ‘temperature rise’ provided by any individual unit. This is the heater’s capability to raise the temperature of the water above its starting temperature. For example, if the heater you’re looking at has a 60 degree temperature rise, and your water source averages 50 degrees before heating, then you can expect the max output of the heater to be water of 110 degrees. Most people use 120 degrees as the maximum heating mark, so 110 might not satisfy you.

    In my research of tankless heating units, this particular problem seems to be at the heart of the issue for some dissatisfied tankless water heater owners. so, when comparing models, make sure you know the average temp of your water supply, and check to see if any model you’re considering can raise the temperature to an adequate level.

  7. Michele says

    Hoping you guys can help us out with this: we’re building our tiny house now and have a utility shed that we’re hoping to use for a propane tankless water heater. It’s enclosed in the shed so doesn’t have open-air ventilation but also isn’t as well insulated as inside of our house (we live in Olympia, WA so it doesn’t get TOO cold here). Should we go with an indoor (that might need more insulation) or outdoor (that might need more ventilation) unit then???

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