Immersion heater element

[drc27wash]

I am looking to fit an immersion heater in my copper tank. I will then be adding a Honeywell Optismart system to divert excess generated power to the heater.

My questions are:
What wattage immersion heater would be the optimum? Low or high (500W to 3KW).

What length heater should I fit?

Do either of these matter?

Any opinions on the best make would be useful. I live in a very hard water area so will be going for a titanium heater.
Many thanks!

[LucMan]

I am looking to fit an immersion heater in my copper tank. I will then be adding a Honeywell Optismart system to divert excess generated power to the heater.

My questions are:
What wattage immersion heater would be the optimum? Low or high (500W to 3KW).

What length heater should I fit?

Do either of these matter?

Any opinions on the best make would be useful. I live in a very hard water area so will be going for a titanium heater.
Many thanks!

50 gallon Residential electric water heaters use an upper and lower element rated at 4500 watts at 240 volts.
The length of the element is not important as long as it fits into the tank.

[Mike90250]

While copper is a nice metal to work with, it reacts with many other things, PH of the water, and other bits of metal in the tank, even the mounting plate of the heat element, could cause a galvanic reaction and start dissolving the tank near the plate.

[hiles8500]

Check out new heat pump water heaters

Lowes and Home Depot are now selling mass market-oriented heat pump water heaters that are more than twice as efficient as the traditional electric water heaters. In many areas the local utility is offering rebates to lower the effective purchase price to be in the neighborhood of old style heaters.

Example: I bought one that listed for $999 and got a $500 rebate from Pepco. The heater will pay for itself in two years, since I installed it myself and had no labor costs. It has side benefits of providing dehumidification and cooling costs to my basement. Yes, it pulls heat from conditioned space in my Maryland house. I'm still ahead of the game over the course of the year. In Texas, it would be even better.

The difference in running costs means that it is reasonable to get rid of your current water heater ASAP even if it is still working fine.

If you want to know more about the pros/cons of putting one of these in conditioned space, look on the web for the study "To Duct or Not to Duct: Evaluating the Space Conditioning Impacts of Heat Pump Water Heaters in the PNNL Lab Homes"

[HVACrepair]

A heat pump might be your best option for efficient heating and cooling. ... cold water rather than air, allowing it to be used with radiant floor heating systems ... A new type of heat pump for residential systems is the absorption heat pump
Heat pump water heaters can help you save energy and money every day.New energy-efficient storage water heaters contain higher levels of ... If you use electricity for water heating, consider installing a heat pump water heater.

[bcroe]

If you use electricity for water heating, consider installing a
heat pump water heater.

I thought a little about that. The heat pump water heater gets its heat by cooling the house
interior, right? So if I am heating the house electrically, and must replace that heat, have I
really gained much? Bruce Roe

[Ben25]

I thought a little about that. The heat pump water heater gets its heat by cooling the house
interior, right? So if I am heating the house electrically, and must replace that heat, have I
really gained much? Bruce Roe

I came to the same conclusion. I haven't bought one yet, but plan to in the next year. What I am thinking is that I will use it in heat pump mode in the summer to cool and dehumidify the basement and electric resistance only mode in the winter.

Ben

[J.P.M.]

I thought a little about that. The heat pump water heater gets its heat by cooling the house
interior, right? So if I am heating the house electrically, and must replace that heat, have I
really gained much? Bruce Roe

Usually that's the case.So, if it's electric resistance space heating, pretty much. But fossil fuel fired space heat may improve the economics a bit in cold regions. OTOH, having fossil fuel fired HVAC and elec. resistance H2O heating heat seems a bit odd.

In warmer climates, and for some applications, it may make some sense to use outside air in winter and some portions of the shoulder seasons as the heat source, and dwelling air during the cooling season. I'd still use CH4 as the preferred choice for space heating where available.

[inetdog]

Usually that's thje case.So, if it's electric resistance space heating, pretty much. But fossil fuel fired space heat may improve the economics a bit in cold regions. OTOH, having fossil fuel fired HVAC and elec. resistance H2O heating heat seems a bit odd.

In warmer climates, and for some applications, it may make some sense to use outside air in winter and some portions of the shoulder seasons as the heat source, and dwelling air during the cooling season. I'd still use CH4 as the preferred choice for space heating where available.

In most parts of the US propane is about on a par in cost per BTU of heating compared to grid electricity. PV electricity is generally more expensive, tipping the balance in favor of propane for off gridders.
But natural gas is far cheaper per BTU than either if it is available piped in. It does not store or transport nearly as well as propane. Compressed natural gas takes very heavy tankage while liquefied natural gas must either be used rapidly or refrigerated.

If you have an unheated basement, you may be able to use that as the heat source for domestic water heater and avoid the need to burn fuel to feed the heat pump. But it is most attractive during the part of the year that you need air conditioning.

[hiles8500]

I came to the same conclusion. I haven't bought one yet, but plan to in the next year. What I am thinking is that I will use it in heat pump mode in the summer to cool and dehumidify the basement and electric resistance only mode in the winter.

Ben

Resistance mode is so expensive it makes sense to use heat pump mode all year. Dehumidifiers are also expensive. There are also costs to putting in ducting. See the study I mentioned earlier for the building science analysis.

[Ben25]

Resistance mode is so expensive it makes sense to use heat pump mode all year. Dehumidifiers are also expensive. There are also costs to putting in ducting. See the study I mentioned earlier for the building science analysis.

Interesting study.

http://aceee.org/files/proceedings/2014/data/papers/1-1203.pdf

I definitely won't be ducting it, and I heat my my basement with electric baseboard. I'll try it in heat pump mode for a year and see. I may get a couple more CTs for my egauge so I can collect HPWH and basement heating data.

Ben

[hiles8500]

Negawatt analysis:

Negawatt is the cost of a saved watt.

Over the 10 year course of operation of my new water heater, it will reduce my electricity demand by 33,650 kWh. Pepco paid me $500 to install that reduction. That yields a cost to Pepco of 1.4 cents per kWh that I don't use.

Pepco can sell that surplus power to someone else for 15 cents, including distribution. I.e., they paid $500 for $5047.50 worth of billable power.

[SirHund]

So just to be clear I am reading that using a 12/24/48 volt immersion element is less than optimal for trying to heat and maintain water temperatures. Unless of course you have a large and dedicated array just for this purpose.?