One Whole-House Tankless Water Heater Vs. Several Points of Use Units?

Whole House or Single Point Tankless Water Heater

When homeowners decide to use tankless water heaters they typically want to know whether they should use a whole house tankless water heater or several point of use units, or zone units. The correct Tankless Water Heater Systemanswer lies within the needs of each house and the family that occupies it. Let’s start with the structure of the home, first.

Existing Homes: Depending on the age and construction type of the house, existing homes can be very difficult to retrofit with electric lines, and running new gas lines is virtually out of the question. Therefore, in an existing home a whole house tankless water heater is usually the best way to go. Another newer option is to install an outside tankless heater. The new Bosch Anti-Freeze system makes outside installation a good option for many applications.

New Construction: If you are building a new home then running electrical lines to each application point for hot water is relatively simple, since the bathrooms, kitchen, laundry room and utility room will already be wired. In addition, if you choose to use gas-fired tankless water heaters rather than electrical, running gas line to each unit is also much easier.

Another clue for new construction is the way the home is constructed. Remember that if you use a whole house tankless water heater then water will be heated at one location and dispersed through pipes to each point of use. Once you turn off the hot water tap there will be hot water still in the line, and that water will immediately begin to cool, which produces inefficiencies and waste. If the home you are building is spacious and spread out this will lead to energy loss. And if you use metered water, you’ll watch your utility bill increase every time you turn on the tap and wait for the water to get warm.

For these reasons many new home projects employ several point of use tankless water heaters. The upfront cost is greater but the energy savings is increased substantially. For example, if your home requires 7 gallons per minute capacity of hot water it will cost less to purchase one unit capable of producing 7 g.p.m., and there are many that do, than it will be to purchase 1 unit with 3 g.p.m. capacity and 2 units with 2 g.p.m. capacity to serve various zones of the home.

However, over time the 3 separate units will use less energy combined than will the one large unit, in most homes anyway. By the way, the need for your particular home is determined by adding up the number of hot water points and their water needs, while also taking into consideration how many points are likely to be in use at any one time. A few examples: bathroom sink, .5-1.0 g.p.m; kitchen sink, 1.0-1.5 g.p.m; shower 1.5-3.0 g.p.m.; and dishwasher 1.0-3.0 g.p.m. Learn how to create a usage audit of your home to help you determine which type of tankless water heater is best for you.

That leads to the second major criterion, the water usage patterns within your family. Home energy experts suggest a whole house tankless water heater when the hot water taps throughout the home are used regularly during the day. Several people getting ready for work or school in the morning use plenty of hot water. A parent at home during the day caring for young children while cooking or doing laundry will use significant hot water. Everyone home in the evening or on weekends will also lead to greater use. A whole house unit is the right choice in these settings.

On the other hand, if certain areas of the home are used infrequently or sporadically – a utility/laundry room that only sees action on the weekend, a guest bathroom and few guests, a jetted tub in the master suite or on the deck that is more of a cold-weather toy – these scenarios make point of use models more cost effective. Break up the home into zones and service the kitchen and guest bath, for example with a 3.0-5.0 g.p.m. model, service the master suite with its own 3.0-4.0 g.p.m. unit and meet the needs of the main bath and laundry area with a 3.0-4.5 g.p.m. unit, as one possible arrangement. The layout of your home will affect the way you select zones.

It should be noted that if you choose to fuel your tankless water heater(s) with gas rather than electricity because of the lower relative cost of gas/propane then a whole house unit makes better sense. It will be more efficient and will save you the expense and hassle of trying to supply gas to 2 or 3 separate locations in the home.

Does this explanation help you decide? Do you have any comments to add based on your own experience choosing a single whole house unit versus several zones? Join the discussion and offer feedback which may be helpful to other visitors to this site!

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Comments

9 Responses to “One Whole-House Tankless Water Heater Vs. Several Points of Use Units?”
  1. jeremy larson says:

    Is there a company or person to contact for help with setup for a new construction project using tankless heaters.

    • Dave says:

      Jeremy: Depending on where you live. A good place to start is your local hardware store like a Home depot. Depending on the size of your poroject they might be able to give you some name sin your area.. Another easy place to get you started is ServiceMagic. your zip code and they will do the rest.

  2. Mike says:

    Gas/propane tankless water heaters are NOT necessarily ‘cheaper’ to operate than their electric counterparts. Electric tankless heaters are almost always more efficient, and this often negates any difference in price.

    • DaveT says:

      Mike: You are correct in analyzing the cost of each type of unit. I also believe that you have to take in account where you live. for example I have a home in town and pay a certain rate for my electricity. I have a cabin which is on rural co-op power and the electric bill is considerable higher per kilo-watt then in town. I would therefore lean towards a propane unit rather then electric.

  3. Dustin says:

    Good afternoon,
    I enjoyed reading the article of yours that I link below, but being from NE Ohio, I am curious what input you might have to my thoughts below.
    I have been thinking about going the route of several POU units in our new home build rather than one whole house unit, but have run across very little on it until I found your article. Having installed two whole home tankless electric systems (one in our home and one in our rental), I really like the opportunity that it seems could be done with POU on a new build.
    Our home will be 1080sq ft and it seems like 5 units would take care of 2 full baths, 1 half bath, kitchen, and laundry.
    My main question is about inlet temperature for the POU units as that greatly decreases the gpm output of them. Our water well will be about 160ft deep. It was hard finding good information, but it looks like even in the winter here the outlet temp from the well water should be ~55-65 degrees fahrenheit. Does that sound correct to you? If that is the case then I should be able to scale down the POU units which would lead to less wiring/breakers/etc. as well.
    Any input would be great, thanks for the article below!
    Dustin

    • DaveT says:

      Dustin: I am not an installer. I ask that all those who follow my site will give some input to Dustins question.

    • Brooke Hatch says:

      Hi Dustin,
      I’m no expert but I’ve done a lot of researching also and had run across something in regards to your question and here’s what I found. Hope your good at math and hope this helps.

      Faucets: 0.75 gallons (2.84 liters) to 2.5 gallons (9.46 liters) per minute.
      Low-flow showerheads: 1.2 gallons (4.54 liters) to 2 gallons (7.57 liters) per minute. Older standard shower heads: 2.5 gallons (9.46 liters) to 3.5 gallons (13.25 liters) per minute.

      Clothes washers and dishwashers: 1 gallon (3.79 liters) to 2 gallons (7.57 liters) per minute.

      Unless you know otherwise, assume that the incoming temperature is 50 degrees F (10 degrees C). You will want your water heated to 120 degrees F (49 degrees C) for most uses, or 140 degrees F (60 degrees C) for dishwashers without an internal heater. To determine how much of a temperature rise you need, subtract the incoming temperature from the desired output temperature. In this example, the needed rise is 70 degrees F (39 degrees C).

      List the number of hot water devices you expect to have open at any one time, and add up their flow rates. This is the desired flow rate for the heater. Selecting a tankless water heater is nearly impossible without knowing the flow rate you need.

      As an example, assume the following conditions: One hot faucet open with a flow rate of 0.75 gallons (2.84 liters) per minute. One person bathing using a shower head with a flow rate of 2.5 gallons (9.46 liters) per minute. Add the two flow rates together. If the inlet water temperature is 50 degrees F (10 degrees C), the needed flow rate through the heater would need to be no greater than 3.25 gallons (12.3 liters) per minute. Faster flow rates or cooler inlet temperatures will reduce the temperature at the most distant faucet.

  4. Brooke Hatch says:

    Hello,
    Thank you for your article, finally some clarity to ask the confusion I’ve been facing. Tankless, point of use, the differences etc. But I still am unsure as to what type (and flow rate) are best for the application I’ll be using it for. So here’s my situation (and any suggestion or advice will be much appreciated, even non professional)
    I will installing and using a 110v tankless water heater in my 5th Wheel/camper trailer. Currently we live in it full time and their are two adults. We currently have a washer and dryer but that had its own water connection point (currently hot water isn’t an option to be run there)

  5. Brooke Hatch says:

    My last question was cut short 🙂 cont’
    We don’t have a dishwasher, we handwash dishes at the kitchen sink and there is one bathroom w a stand up shower and separate sink. There is one inlet water connection point on the outside of the trailer where cold water comes in. And hooked to our kitchen sink is a 10 gal “low boy” 110v electric water heater. It runs out during one shower and or one load of dishes. Then we have to wait another 30min at least for it to heat back up. For this reason and then obvious space saving reasons we want an electric tankless water heater or a point of use. Which one would be best suited for us and can or should it be installed inside or outside? Thanks again for all the information!

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