Electric tankless water heater or not

14 years ago

I am trying to decide whether to get an electric tankless water heater or a regular electric water heater. I understand that tankless does require upgrading electrical service and often is not an economical choice. My situation does have some factors that cause me to consider. Situation is as follows:

1. Just bought existing house that currently uses propane. Existing water heater is in the utility room. The only location for it in that room is in front of the freezer resulting in only being able to halfway open the door. So that is not a great location for a regular water heater. House is a 2000 sf one story house. Also as currently installed the T&P drain line slopes upward and does not have gravitional flow. In any event, not sure where else a regular water heater could be placed other than the utility room. If anyone has ideas would consider it.

2. Live in Texas, near Houston to it is not usually that cold.

3. Electrical panel is undersized and has a number of problems so we are changing the electrical panel and upgrading from 125 amp to 200 amp service even if we don't get a tankless water heater. We want to convert the house to all electric water than having propane at all.

4. To go tankless, electrician recommends 225 amp service instead of 200. This costs an additional $500 over the 200 amp service we would betting for a standard water heater.

Also for a standard water heater, he would install a 120/240 volt 40 amp circuit. For tankless he would install a 120/240 volt 120 amp circuit which is $535 more. So the extra electrical for the tankless water heater is a total of $1035 more.

I don't love the idea of spending $1035 more for tankless. I am willing to do it if the tankless will be advantageous or if I will be able open my freezer door! With the tankless there would be room to install it and still open the freezer door. Without tankless I would either have to lvie with the freezer door issue (I don't want to) or find somewhere else to relocate the water heater, but not sure what is feasible.

Oh, house is 2000 sf, there are 4 people living in it now. In a few years there will be 2.

Any thoughts?

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Comments (5)

jakethewonderdog
14 years ago
I think you may be under-sizing the tankless and the electrical.

A unit that draws 100 amps and uses two 60 amp breakers would produce 5 gpm (two showers) @ 105 degrees with 70 degree water going in. If the water inlet temp drops to 59 degrees, it's 3.8 gpm - not two showers.

I think that's borderline for a family of 4 unless you tell me the water inlet temps remain 70degeees or more.
kats_meow
Original Author
14 years ago
How do I find out what the water inlet temp in this area would likely be? In Texas, near Houston.

House has two bathrooms so probably not that difficult to avoid two people taking showers at once. Might have shower and dishwasher running at same time.

If it is undersized, what kind of options might exist to relocate the regular water heater? What kind of space would it need?
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I think there are a lot more folks here who have experience with the gas tankless heaters. Thus the lack of response. The main issue w/ electric on-demand heaters is the massive amp draw to heat the water. I did a quick look, and one unit that'd do 2 gpm at a 60 degree F temperature rise (maybe enough for your shower and sink in the winter) takes 80 amps to do that. That might require a service upgrade that'd be pretty painful financially. And I'm not sure if you can run a conductor that big inside your walls without conduit as protection. You've probably read that gas heaters have their own issues. The equivalent one is the need for a large gas feed (and possibly a new meter to meet the demand). But that's relatively low-tech piping that has to be run. Ditto on the need for expensive vent piping if you put one inside. And don't forget that, if your power goes off, no hot water. I guess there's some potential to mount a gas tankless on an outside wall, which is what we did with our Noritz. That gets rid of some of the issues, but then you need to make sure none of that piping is going to freeze. I'm in GA, and piping in outside walls makes me nervous here. That'd increase by a big amount for the DC area. There are lots of pros/cons/tradeoffs. Putting a bigger (and preferably more efficient) tank heater in your basement likely is going to be the cheapest option. Going to either type of tankless will save you on waiting for hot water, and it may save a little on energy usage, but that's going to come at a significant additional cost.
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You'll need more electric service than you probably have. Electric tankless units use from 80-150 amps. Typical home construction usually now has 200 amp panels, and you'd need to upgrade brand new construction to more capacity, much less an older home or apartment building. 20 years ago, 100 amps was "normal" service to most homes, and there are still plenty of places that only have 60 amps of service. Upgrading your electrical service will be costly, and even more costly if your bulding itself will need an upgrade of it's feed to be able to supply you. That is, if your building will even allow you to upgrade anything at all. Many will not. The first thing you need to do is to determine the capacity of your electrical service, and the capacity of your bulding's service. That'll tell you right there if it's even feasable to spend a couple of thousand upgrading your individual service. If the building itself will require more service, expect the fees to be in the tens of thousands of dollars in your particular locale. Because if they allow you to request and pay for an upgrade, they'll probably want to size the building with the anticipation of everyone in the building demanding an upgraded service.
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To achieve 4 GPM at 60 temp degree rise it with require about a 30 KW unit. Which should be adequate for two 2.5 GPM showers set at 105 degrees. At 240 volts (most homes have 215-230, so even less output) it will take 120 amp service alone to heat the water, even on a 200 amp service, doesnÂt leave you enough to run heat pump, dryer, range/oven and lighting. In addition you mention turning off gas at furnace so will you be adding more electric coils to the ductwork for when the heat pump canÂt keep up when itÂs cold out? If you hate gas that much, install a 60 gallon plus electric water heater, pull furnace and install air handler with electric resistance back up heat, and then complain about the high energy bill while the rising electric costs continue to climb since they are closely tied to Nat gas costs because of production. Most people donÂt have a concept of how much input or energy is required to heat water with electric, especially on-demand units. Look at the gas units, instead of a 40 gallon tank with 40,000 BtuÂs the gas on-demand units are 200,000 BtuÂs to meet the draw demand.
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I agree that electric tankless for this use could be appropriate. Here's the thing to know: There is no magic. The amount of throughput (GPM) is math - and is entirely governed by the amount of current it draws. Nobody has any design that gets more GPM for less current. Here's another tip: You may have 200 amp service (meaning the breaker and such) - but I've seen plenty of times, particularly in rural areas, where the lines going to the structure from the utility were way undersized and no-way would they sustain the 80% of the service rating. I think the 27 is the size you would want. A shower is considered 2.5 gpm. Given your deep well, you would likely be able to run your shower with a little left over. You can eliminate some guesswork if you actually measure the temp of the water. Of course a small tank heater would solve a lot of issues, but I understand you don't want that.
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weedmeister
14 years ago
For $1000, I'd move the freezer.
wisehvac
14 years ago
stick with propane and get a tk-3 get the outdoor model if it doesnt frezed in ur area
dadoes
14 years ago
Kats_Meow,

I'm in TX, SW of Houston. I'm on a private well, semi-rural area at edge of my town. My pump tank is in my (detached) garage. My well and (submerged) pump is wayyyy around on the other side of the property due to logistics and requirements of sufficient space for both a well and septic, so it's a long (but underground) run from the pump to the tank. During the occasional cold snaps like this past winter, incoming water temp can drop to less than 40Â°F. In heat of the summer it may be 80Â°F or a tad more. My electric tankless is a 120amp unit. It doesn't have any problem generating 135Â°F to 140Â°F output when I (occasionally) want that high a temp for washing a load of whites. Otherwise I set the tankless at 100Â°F to 102Â°F in summer, 104Â°F in winter for normal use. That low temp is fine for dishes, my dishwasher has on-board heating and can work with a cold input. My tankless unit varies its power draw per the input temp, output temp, and flow rate. It may operate at little as 5% of full power or at 85%+ ... so obviously it doesn't always pull 120 amps, but the circuit must be able to supply full power when needed.

Electric tankless water heater or not

Comments (5)

jakethewonderdog

kats_meow
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Electric tankless water heater or not

Comments (5)

jakethewonderdog

kats_meowOriginal Author

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kats_meow
Original Author