Does anyone know about "tankless" (aka "instant" or "on demand" water heaters?

Parent Cafe
1

<p>We need to replace the old tank water heater that services our master bathroom (shower, separate tub, and two sinks) and we’d like to be energy efficient. Tankless heaters (on-demand) have the benefit of heating water as it passes through them, and as a consequence, don’t waste heat on water that’s never used. But I have several concerns about them - has anyone had experience they could share? We have a total electric house and installing natural gas would be too costly. LP gas could be an option, but I hear that electric heaters are 98% efficient vs. gas at only 85%.</p>

<p>1 - Can such a device really heat ground water (note: ground water in central Georgia) to shower temperature as quickly as it takes two gallons to flow through in a minute? Think of how long it takes two gallons to heat up on your stovetop. If a tankless heater can do it instantly, why isn’t that technology used on stovetops and in coffeemakers?</p>

<p>2 - Our showerhead flow is 1.5 gal. / min., and these devices are supposed to handle that volume. But I’d guess that the tub flow is much greater. Would we be able to fill a tub with hot water? (30 gal. in the tub at a flow as slow as our shower would take 20 minutes, by which time most of the early flow would have cooled off?)</p>

<p>3 - I don’t anticipate that any of these four faucets would have to run simultaneously, but would it be possible to have a single point of use device that could be connected to all four taps?</p>

<p>4- Would you think that a tankless heater could effectively heat water in our midwinter? Obviously, running water will never be colder than 32 degrees, and I think that our typical groundwater temperature is around 60.</p>

<p>Thanks for your feedback!</p>

2

<p><a href=“http://talk.collegeconfidential.com/parent-cafe/582282-water-heater-popping-replace-tankless-whs-your-experience.html?highlight=tankless+water+heater[/url]”>http://talk.collegeconfidential.com/parent-cafe/582282-water-heater-popping-replace-tankless-whs-your-experience.html?highlight=tankless+water+heater&lt;/a&gt;&lt;/p&gt;

<p>we previously discussed this issue awhile back.</p>

3

<p>Six years ago we completely remodeled our home and installed Tankless Hot Water Heaters. Our contractor did every thng in his power to talk us out of them, but I was determined to have them, and guess what? They are incredible to have. We ALWAYS have hot water and never run out! The only downside is that when we go on vacation, the kids tend to use all the hot water because the real world is not like home. The key to success with tankless hot water heaters is to ensure that the tank is large enough for the area in which you are using them. We installed them for the various zones in our home. Our utility bill benefits because we do not have to keep a large tank heated. I would never live in a home without them again.</p>

4

<p>I don’t understand why plumbers and contractors often argue against them. I don’t know anyone who has them who doesn’t love them. The main argument I’ve heard against them is that some people take longer showers because they don’t run out of hot water. There was an excellent article in Fine Homebuilding which also talks about some disadvantages and how to fix them: [Why</a> Add a Tank to a Tankless Water Heater? - Fine Homebuilding Article](<a href=“http://www.taunton.com/finehomebuilding/how-to/articles/add-a-tank-and-pump-to-a-tankless-water-heater-to-save-energy.aspx]Why”>Why Add a Tank to a Tankless Water Heater? - Fine Homebuilding)</p>

5

<p>They are NOT instant. Most installs include an infrared sensor to turn on the thing whenever a person enters a room with a hot water spicket because they need a minute or two to get up to temp, which amounts to wasted energy if you don’t use hot water. (Think: going into the bathroom just to use the toilet.) But if you can wait a minute or two, then they become worthwhile.</p>

6

<p>We are on tankless, 22 years +. Oregon gives a tax credit and the gas company gives an incentive to install a high efficient water heater. I think there is now is a federal credit. The water is on-demand, meaning that water is heated as soon as you open the spigot. It is very fast and hot enough. </p>

<p>We do not have a infared sensor but a pilot light. Newer models use electronic ignition.</p>

7

<p>I looked at the link above and thought I’d add a few more things here specific to your situation.</p>

<p>Yes, they have electric on-demand water heaters.</p>

<p>You will have extra expenses depending upon your current (no pun intended) electrical service.</p>

<p>The water type (ground or surface) has little bearing on the ability to heat (although softer water will delay the degradation of the heating capacity.</p>

<p>First thing to know is that all on-demand water heaters are measured in how many gallons per minute of how much temperature rise. In other words a unit may be rated at 1.5 gallons of 50 degree rise. </p>

<p>Considering that your home hot water system should never be set to more than 120 degrees (safety issue) you need to know the approximate temperature of the water entering your home to calculate how much capacity you need to buy. A good source for this information may be your local water utility. If you live in Georgia, your winter water temperature probably is never below 50 degrees, while the folks in MA will have cold water around 40 degrees. That is a big difference in how much capacity you would need between the 2 locales.</p>

<p>If you have 2 showers running at 1.5 gallons per minute each (3 total gallons) at a typical 100 degree output (mixture of 120 degree hot water + X degree cold water), you will need to know how many gallon degrees of output your unit can contribute to this. If your coldest cold water is 50 degrees you will need 3 gallons per minute of 50 degree rise to run 2 showers.</p>

<p>Next issue - Electrical capacity. Your current electric tank water heater probably runs off of a 220 dedicated circuit. You will need to upgrade the electrical output to match the demand for the on-demand heater. This may involve any or all of the above - rewiring to heavier gage wire, adding more amps to the circuit, upgrading you total home service.</p>

<p>If you think upgrading electrical is bad, don’t ask about gas. For a typical gas on-demand heater you need 3/4" pipe directly to the heater. Most homes run 1/2" to their appliances except the furnace. And most gas installations also require an electrical box to be located at the site (not necessary with most gas water heaters), so most folks also have to have the electrician come out anyway. And with gas, sometimes you also have to change your flue diameter as well. So you probably don’t want to think about gas or propane.</p>

<p>That being said, I have a friend who put in a small (gas) tankless (no gas upgrade required, but very limited capacity) unit inline with an old water heater that he converted to be a storage tank from a small solar preheating unit he installed on his roof. From the beginning of May until September, his on-demand unit never turns on. He does turn it off (and drains it) in December for 2 months. I believe he has a setup where he can use the on-demand to keep the tank at a set temperature (tricky plumbing here) of about 75 degrees and use that water to supply the on-demand unit for domestic use (reducing the rise necessary to supply hot water to his house). However, he is an engineering professor and for most of us this would fall under “don’t try this at home”. </p>

<p>One last thought- if you are in the market for a ground-source heat pump, they come with the option of including a hot water system (free to operate during cooling season because it takes waste heat from the A/C - cheaper than resistance hot water heating - tank or tankless electric - in the winter because compressors are more efficient). Big capital investment though - the compressor costs the same as a regular heat pump, but count on $5K in drilling holes in the ground to bury your heat sink. But your heating and cooling costs are typically 40% cheaper and generally pay for themselves in 7 to 10 years. YMMV</p>

<p>I’ve probably got your head spinning by now, so I’ll basically leave you with the thought that you will have a significant capital investment to make if you choose to change your thermal management (water or air). However, if you have the money to invest and intend to live in your home for a while, it sure beats the stock market :wink: .</p>

8

<p>We have one. It is amazing. My father is a master plumber and a huge advocate for them. </p>

<p>Plain and simple- they save money, electricity, and allow you to do numerous things at once. They really are as good as they sound IMO.</p>

9

<p>Have used them in modest hotels in Thailand. They are fabulous, and I would certainly install one if I had the chance.</p>

10

<p>Note: I don’t think they make electric whole house demand how water heaters. The discussion below is for Gas Whole House Demand Water Heaters.</p>

<p>

</p>

<p>Yes. They use as much energy (BTU’s) when in use as your furnace. Why don’t they use them on stovetops? Because your entire stovetop would be ONE burner. Also, you would then have to have a flu to exhaust the gas (CO2). You don’t want to use something that big as your kitchen stove. It would also be like putting a blow torch to the bottom of your pot. Your pot may not last as long.</p>

<p>

</p>

<p>The larger demand units can handle two users at the same time (2 showers, shower and laundry, etc). I suspect they would not have a problem with a tub at a reasonable flow rate.</p>

<p>

</p>

<p>I think you are confusing the instant heaters that are under a sink vs. the demand units that replace your hot water heater. The electric instant units have a little tank that fits under the sink. The flow rate is fairly low, but it can put out boiling water. Think filling a cup, not a dish washer.</p>

<p>A gas demand unit replaces your whole house hot water heater, and will cover all your hot water faucets.</p>

<p>

</p>

<p>Yes. They are designed for that. Look at the flow rate at different rise in temp rates. Since you are heating from 60 degrees worst case, you could possibly get a smaller unit.</p>

<p>My municipality uses lake water, so the temp can get into the 40’s during the winter. In order to get a unit that could serve 2 showers simultaneously, I would have had to get a unit that required a sealed 5 inch exhaust vent. The exhaust vent alone cost the same as the heating unit. However, on new construction, the incremental cost is negligible.</p>

<p>I have also heard that the demand units require periodic cleaning (I think every 2 years is recommended by the manufacturer). Think about all the sediment that collects in your hot water tank. Some of that collects on the heat exchanger, and needs to be chemically cleaned out in order to maintain the heat exchange rate (flow rate). I hear the cleaning can be expensive.</p>

<p>Tankless heaters are used alot in Europe because they are smaller (don’t have a tank). However, space tends not to be an issue in the USA. Net-net: I think tankless heaters are great if you tend to run out of hot water (rather than buying a larger tank). Otherwise, the savings is offset by: cleaning costs and longer showers. Running out of hot water is one way to force dicipline on the length of showers.</p>

11

<p>Thanks, all. Isn’t it amazing that we can get on the cafe, ask something completely unrelated to colleges, and get this kind of feedback?</p>