What Size Tankless Hot Water Heater Do I Need?

Lately, tankless h2o heaters are gaining a lot of traction thank you to the assortment of perks that it comes with. High free energy efficiency, on-demand unlimited hot water, modest meaty size, and low energy bills are some of the best things virtually this engineering science.

So yeah, switching from your old tank h2o heater with a tankless h2o heater or ownership one for your new home project can be a nifty decision.

Merely the big question is;

What size tankless hot water heater practice you lot need?

Get a pocket-sized one for the sake of saving money and curse yourself for years cause yous never get plenty hot water. Or buy a bigger 1 than you need and spend extra when it wasn't required. That'south why proper size is fundamental for peace of mind.

Simply before nosotros size, what'due south different with tankless h2o heaters?

Unlike tank water heaters, tankless does not store hot water. Instead, it heats and delivers hot water instantly and on-demand.

In that location's an upper limit to how much hot h2o a tankless h2o heater tin deliver per infinitesimal which is measured in gallons per infinitesimal or GPM and it'south an important factor when sizing a tankless system. Learn most the pros and cons of tankless water heaters here.

Things you need to consider while deciding the size of the tankless water heater

Determining the size of a tankless water heater that's all-time suited for your household tin be like shooting fish in a barrel if you know what to look for.

Following are the only two things that you lot demand to figure out to find out the suitable size for your needs.

ane. Temperature rise

Temperature rise is how much temperature of the cold water is needed to be raised to get to the desired temperature. The colder the water, the higher the temperature rise will be.

It is an important factor when it comes to the hot water output of your tankless water heater. This is because the colder the water, the harder the heater has to work to raise the temperature.

Ok. To observe out your desired temperature rise, you need two temperature data points.

Start up, yous need to find out the groundwater temperature at your habitation. Y'all can utilise a thermometer to find that or cheque out this Usa map beneath for average temperatures in your region.

US groundwater temperature map — Average groundwater temperature. Image: HomeDepot.

For instance, in Florida the groundwater temperature is 77°F.

Next up, the desired hot h2o temperature. Commonly, people use 105°F hot water for the shower.

Yours can exist different.

At present subtract common cold water temperature from desired hot water temperature and you get your temperature rising.

Desired temp. – groundwater temp. = Temp. Rise

For the higher up state of affairs,

105 – 77 = 28°F

The higher the temperature rise, the lower the maximum hot h2o menstruum rate gets. That'south why the same tankless water heater that delivers 5 GPM hot water in Florida can just return 2-iii GPM hot water in Alaska or Minnesota. Because the h2o in Alaska is twice as common cold in Florida and thus heater has to piece of work double hard.

2. Summit hr usage

Now that hopefully, you lot know the desired temperature rise you need, the next stride in sizing a tankless water heater is PHU.

PHU or peak 60 minutes usage is the maximum number of hot h2o fixtures y'all tin possibly use at the same time.

It'south important, cause equally said before, there's a limit to how much hot water tankless units can evangelize per infinitesimal and you lot volition want to make sure that it delivers enough to satisfy your peak hour usage.

So think about the fourth dimension of the day when there's a lot of hot h2o usage.

For nigh households, it's morning time time when someone is in the shower, another using the bathroom sink to brush teeth, and female parent preparing nutrient using the kitchen sink.

Y'all have to determine how many maximum hot water outlets you tin can use at the same fourth dimension and add that up to detect your peak hour usage in GPM.

If we consider the instance discussed above so,

Shower (2 GPM) +bath sink (1 GPM) + kitchen sink (1.5 GPM) = 4.5 GPM

Yous will accept to look for a tankless water heater that can deliver hot h2o at 4.5 GPM. * The above GPM values that we calculated are standard and the GPM of fixtures at your domicile could be unlike.

The standard flow charge per unit of unlike fixtures

Fixture	Flow Rate (GPM)
ShowerHead	2
Bathtub	2.5
Bathroom Faucet	1
Kitchen Faucet	ane.v
Washing Motorcar	iii

The above flow rates are national averages and the flow rate of your fixtures could be unlike. Employ this guide at the spruce to measure the flow charge per unit of your fixture.

three. Adding up

Now you know your temperature rising besides as your pinnacle hour usage so at present all yous have to exercise is search for a tankless h2o heater from your favorite brand and attempt to match these parameters. If we consider the above example then nosotros need a tankless water heater with a minimum 4.5 GPM flow rate at a temperature rise of 28°F.

Now permit's take another example and then you tin better understand the sizing concept.

Tankless h2o heater sizing instance

Suppose you are a family of 4 living in Minnesota with a groundwater temperature of 38°F. You accept two bathrooms in your household and would like to employ 2 showers and a kitchen sink at the same time. What tankless water heater size you should look for?

Solution. First up, 38°F is your incoming common cold water temperature. To take shower or for a kitchen sink y'all would, let's say, need 110°F hot h2o. And so the temperature rise here is 110-38=72°F.

Side by side, two showers and a kitchen sink are your meridian hour usage. If we summate total GPM based on standard GPM of shower head and sink faucet, and then

2+2+1=v GPM.

And then for the above example, yous volition need a tankless water heater that can deliver hot water at 5 GPM with a minimum 72°F temperature rise. You need a tankless h2o heater that can lucifer or exceed this specification.

Fix with your size? hither are the pinnacle electric tankless water heaters that you can choose from.

How to non size a tankless water heater?

Finding the correct size of tankless water heater tin be intimidating especially if you have been using a tank and are new to this applied science.

And there are some wrong ways people use to size a tankless water heater that may cause you to inconvenience down the line. Then allow's simply go to know them first mitt.

Outset, never just try to deduce the size of the tankless water heater based on the number of family members. While it may seem logical but it's non a tank water heater that you will want to make sure have sufficient h2o stored for everyone.

Also, a lot of people might think this manner, merely replacing a l-gallon tank h2o heater with a 5 GPM tankless h2o heater is not the correct way. This way, you would undersize or oversize as well.

So the best way to size a tankless h2o heater is, yes, mentioned to a higher place, acme hour usage and temperature ascension.

Gas or electric tankless h2o heater?

This might not make a lot of deviation in warmer climates but it does in colder ones and for bigger families.

Gas-powered tankless water heater tends to heat water faster than electric counterparts. So these are more than suitable for the colder, southern regions.

Besides, gas tankless water heaters tend to terminal v-7 years longer than electrical units.

The drawback notwithstanding with gas models is the higher upfront cost. Gas tankless units can cost twice as much compared to electric units. And and so there are venting and gas lines that you demand to accept care of. Learn more about gas vs electric water heaters hither.

Hi! I am an HVAC technician and author of HWT from Aberdeen, South Dakota. I have been providing plumbing services for over a decade now. With 10+years of feel in the field, I more often than not have worked with water heating systems. With the assistance of this web log, I am expecting to share some of my experience and knowledge in the field with yous.