Water heater advice - convert/modify summer winter oil burner to tank-less electric heater?.

[Skal7713]

I just bought a home which has a summer winter oil boiler system for hot water. Historically between March and September oil use has been about a gallon/day heating hot water in a home for two people. I really want to replace it with an electric tank-less though it is difficult to find good data on whether this would be more efficient. Here are some points I am considering. Feel free to comment on any points as I am looking for advice:

1) This is a 3 bedroom house, and even though only I am here I would like whatever system is installed to scale to future occupants if it is a larger family. There is only 1.25 Baths plus Kitchen with dishwasher and a washing machine to compete at once for hot water. Which system would be adequate for this scenario.

2) I am limited to a currently installed 100 Amp breaker box. The power company will bring free of charge a 200 or higher amp service to the house. Is there a creative way to add another box to allow for the higher amp service coming in and provide for the electrical draw of a tank less electric water heater without having to replace the entire 100 Amp box with a 200 or greater box?

3) Is there a good practice for installing the tank-less heater in such a way that in the winter when the furnace is on, I could still preheat hot water in the boiler which is running anyhow and then feed the tankless water heater and make this work?

4) Given these factors is there a formula to calculate whether I will save money on energy costs?

Thanks in advance for any advice. I realize this topic spans the scope of the different forums since it is both about the electric tankless and the summer/winter oil burner boiler.

Skal7713

 

[BadgerBoilerMN]

First the cost of available fuel.

Then the design load, how much water you will need.

Finally, the cost of equipment, maintenance and operation.

Dual-fuel systems are difficult to design without some sort of storage. We use a Marathon electric tank with wood primary when the weather is cold.

We design all kinds of integrated systems using boiler, tankless, tank-type and any fuel that makes sense.

 

[Sponsor]

 

[Dana]

An electric tankless to support even a single shower in PA would require a dedicated 50A 240V circuit. Electric tankless may make sense FL, or as a point-0f-use water heater in cold-water states, but as a single whole-house hot water heater it's a terrible idea in PA.

A better solution would be to plumb an electric tank HW heater in series with the coil in the boiler, with a bypass branch and isolating valves so that you can turn the boiler off in summer and switch the feed cold water to the tank without running cold water through the boiler when it's off (which could cause unwanted condensation and corrosion in the boiler), while still pre-heating the water headed for the tank with the boiler in winter. In that scenario the heater elements never (or rarely) come on when the boiler is active, and when you mothball the boiler for the season you flip two ball valves to switch the water feed to the electric tank.

More expensive (but still worth considering) would be to install a heat pump water heater in the boiler room with NO connection to the boiler coil, which would harvest the standby & distribution losses of the boiler in winter, and keep the humidity under control in summer (since the heat pump water heater also dehumidifies the room.)

That also lowers the heat loss out of the boiler room in winter (by dropping the average temp a degree or two), and would allow you to run the boiler at a lower temp for lower standby & distribution losses (which would also lower the heat loss out of the boiler room). To get reasonable hot water performance out of an embedded coil usually requires standby temps of 160F or higher, whereas if you don't need to use the coil you'd be able to run it at 140F at the low end, or even cold-start it, if it's a cold-startable model, which would require some minor control changes. Below 140F you run into corrosive exhaust condensation issues on the heat exchangers in many oil boilers, so don't go there without researching it first.

By lowering the heat loss out of the house with this approach you'll save oil in winter, and use less than half the electricity for heating water in summer.

 

[WorthFlorida]

... really want to replace it with an electric tank-less though it is difficult to find good data on whether this would be more efficient...

1) This is a 3 bedroom house, and even though only I am here I would like whatever system is installed to scale to future occupants if it is a larger family. There is only 1.25 Baths plus Kitchen with dishwasher and a washing machine to compete at once for hot water. Which system would be adequate for this scenario.

2) I am limited to a currently installed 100 Amp breaker box. The power company will bring free of charge a 200 or higher amp service to the house. Is there a creative way to add another box to allow for the higher amp service coming in and provide for the electrical draw of a tank less electric water heater without having to replace the entire 100 Amp box with a 200 or greater box?
Skal7713

SKAL, Most people get efficiency and confused with lower cost! They are different. Efficiency is getting the most heat or energy from the energy source. Here is a good site with info http://www.energykinetics.com/savingsHeatingFuelComparisons.shtml

Lower cost usually results from higher efficiency when staying with the same fuel source but changing over to electric may result in higher cost or lower all depending where you live. But one thing for sure the cost to convert may take years to recoup.

Your electric company will not just connect you to 200 amp service without have first done a lot of changes. You will need to have a licensed electrician, sometimes they must be an approved contractor by the electric company. You will need to change out the electric panel because it needs to have a 200 amp main breaker and most likely the wire gauge from the panel to the meter box will need to be increased. In some areas the main is at the meter in a box below the meter box with room to add breakers on the outside of the home. The meter box may need to be replaced for the increase of amperage but an old meter connection may have corrosion, and, it must have a permit pulled and pass inspection before the electric company will give you the connection.

Cost will be in the thousands no matter where you live in. Call an electrician in your area and ask them what the average cost might be to convert 100 to 200 amp service. Trying to save money with electric, maybe not.

 

[Jadnashua]

Assuming you have room, you could run your upgraded service to a new panel, and convert your old panel to a subpanel. That would require separating the neutral and ground busses and running a new cable to it from a breaker in the new panel. Lots of room for a new breaker for an electric WH. Let's say it did call for a 50A service, that doesn't equate to an awful lot of BTU's. You'd probably have to derate it by the 80% rule (not sure), so you'd actually be limited to 40A on that 50A circuit so 40*240=9600W 9600W*3.4BTU/W=32640BTU. That's about the same amount as a typical electric tank-type WH. A typical gas-fired tankless system can be nearly 200,000BTU, or about 6x more energy, and even those can have issues raising water temps in some situations. An electric tankless may need to be lots bigger than 40-50A service to do much for whole-house use.

 

[Master Plumber Mark]

personally I think you would have to be nuts to do this.... upgrade the power system
probably will need a water softener to keep the water going through the heating elememts clean
need to de-lime the thing once or twice a year...

you are attempting to squeeze the last penny you can out of the deal and its only
going to come back and bite you in the ass someday...because people that can repair one of
those electic tankless dogs are very hard to find when you need one.. if any actually exist....


Electric tankless heaters are a joke .... odds are you wont be happy with it.
So if you have the room, why not just install a 50 gallon electric
and keep things simple??? There is only so much blood you are gonna squeeze out of this before it becomes
too much trouble and effort.