Guide on How to Choose What is Right for You
Keep in mind that they are a bit more expensive than their tank counterparts, and can be a lot more. The low end we’re looking at here is around $500, with the high end at well over $1000.
This isn’t including expert installation, which I do recommend. While some of the risks of installing a natural gas heater are avoided with an outdoor unit, it’s always best to have somebody who knows what they’re doing fiddle with anything involving plumbing or electricity.
Gallons Per Minute
Abbreviated to GPM, this is how much liquid flow your unit can handle at a given temperature. We’re mostly going to be looking at whole house units today, ones that can serve as your only unit. To that end, some numbers to keep in mind:
-A shower uses between 2 and 2.5 GPM. By regulations in place since the 90’s in the US, 2.5 is maxed for a faucet or sink can output by law.
–A faucet, counterintuitively, usually uses just a bit more GPM than a shower (since it has a more open flow). A bit less for kitchen or bathroom sinks, but more for a tub. Expect between 2.1 and 2.5.
-A dishwasher runs at about 1 GPM, and your washing machine barely hits .25 GPM.
-Most GPM estimates on a unit will be assuming it is raising the fluid temperature somewhere between 30 and 45 degrees, so keep in mind that you’ll have to be more conservative if you live somewhere the groundwater is colder. 5 GPM with a 45-degree rise may be only 2.5 GPM with a 90-degree rise, as an example.
If you crank the heat up to the point a hater can’t handle the flow, you’re going to get cold bursts, and that’s never fun.
British Thermal Units
Knowing the BTUh (the amount of BTUs it outputs per hour) output of your product will let you determine if it gets hot enough to handle your needs if you live somewhere cold.
That means sometimes you might need to do a little quick and dirty math, so here’s your reference:
-1 BTU is enough to raise 1 lb of water 1 degree.
-A single gallon is 8.3 lbs (so 8.3 BTUs = 1 gallon raised 1 degree)
-Groundwater temperature varies by location, the lowest being about 30 degrees in the US.
-To get a comfortable shower, most people prefer it be at least 90 degrees (though that’s a bare minimum; I set mine to 115 degrees). So if you live in a place where it is 30 degrees, you want a unit that can raise that temperature by 60 degrees at least with a decent flow.
There are two main types of tankless heaters: Propane (or natural gas) and Electric.
Both have their pros and cons, but in general Electric units are the most efficient (having a 99% heat transfer efficiency) while natural gas units are less so ( around 80% though condensing units are nearly as efficient as electric).
The main swap comes around when you factor in cold weather; Most Electric units lose 2/3 of their efficiency in cold weather, while propane units stay just as effective in all weathers.
It’s also worth noting that in the short term propane is slightly cheaper than electricity, though the cost of propane is rising faster than the cost of electricity every year.
As with anything, these units take up space. While they take up way less space than tanks, you should always keep in mind two main things:
-The building codes where you live. This particularly applies to apartments and mobile homes, which may have strict practical and legal limits for how big or heavy something you can install can be. You’ll run into it with air conditioning as well.
-Total space available. The measurements I’m giving here are only the measurements of the unit itself, remember that you need proper clearance on all sides (the more the better) to avoid something overheating or catching fire. This applies doubly if you’re putting something in an outdoor shed or storage space; you can’t install the unit too close to the walls or ceiling for safety reasons.
On a lesser note, consider shipping costs where free shipping isn’t available. Even if you’re already buying an $800 unit you may be swayed to a similar unit just because it’s smaller and lighter, and this costs less to ship.
Now that we have that settled, on to the reviews!
Our Review of the Top Rated Models on the Market
Kicking us off is Takagi, a respected name in the business, if a bit less well known than Rheem and Rinnai.
This is a propane unit with a 6.6 GPM flow rating and a respectable 140k maximum BTUh. It operates at a slightly higher than average 82% efficiency for a propane model. Take note that this 6.6 GPM drops to between 2.5 and 3 GPM for colder weather, making it mostly useful for very small homes in colder climates, but good year round in warmer weather.
It’s about the average size for a unit like this, at 6.7” x 13.8” x 20.3”, meaning you can install it pretty much anywhere on the side of your house.
It lacks many of the special features other units have (though can be remote controlled, which is a near necessity with an outdoor unit), but that’s because this is a budget option: It will only set you back around $500, an excellent price for its admirable performance.