Thinking of going to an electric water heater

**pete c** · 01-23-2011, 01:36 PM

With oil prices being what they are, I have been considering going to an electric water heater rather than the tankless coil.

I realize that oil BTUs are cheaper than electric ones, but, with oil getting more expensive, I'm not so sure that the difference is that big.

I would leave the tankless coil in place to heat the water during cold months when the boiler is working anyway. I would add the electric water heater down stream of the coil. It would handle all the heating chores when the boiler was off and serve as a tempering valve, sort of, when the tankless was providing the hot water.

I currently have a tempering valve, but, it seems to not be doing the job currently. I suspect it needs cleaning/replacement. If it does need replacement, I would probably just go ahead and get the electric heater and do away with the tempering valve.

Any suggestions appreciated.

**jadnashua** · 01-23-2011, 03:29 PM

Keep the tempering valve! In-tank coils typically have a fairly low gpm flow rate, especially in the winter when incoming water temperatures can get quite cold. Depending on which costs less, you could add a recirculation system to use in the winter and turn the electricity off to the tank. Put the tempering valve on the outlet of the new tank, and the hotter water from the coil might get the new tank quite warm, then tempered to a safe level.

**pete c** · 01-23-2011, 03:51 PM

i think i get what you are saying. recirculate the water through the coil, basically turning the electric heater into an indirect, sort of.

**jimbo** · 01-23-2011, 03:57 PM

Since many places burn oil or gas to make electricity, I don't see a reversal of the price advantage coming!

hj · 01-24-2011, 06:14 AM

You need to rethink your idea, or get an professional's input. If the heater is "downstream" of the coil, it also has to be downstream of the tempering valve because a coil's temperature output is "unregulated", and you do not want the tank to get overheated. If it is "upstream" of the coil, (and upstream/downstream depend on which way you are thinking of the flow), then your electrically heated water is going to try to heat the boiler's water as it flows through the coil. Electric is NOT usually an "inexpensive" way to heat water and is usually the last choice if there are other fuels available.

**Dana** · 01-24-2011, 08:14 AM

Originally Posted by jimbo

Since many places burn oil or gas to make electricity, I don't see a reversal of the price advantage coming!

Name one non-island place in the lower 48 of US with a population of over 1000 that uses oil as the primary (not peak) power generation fuel. (There might be one, but I don't know where it is.) Oil has been too expensive to use even for peak-generation ever since the price spike of the early 1980s except in the rare case.

The price of natural gas is not in lock-step with crude oil the way heating oil is, and has a significant $/MMBTU advantage over #2 distillates (albeit behind coal by good measure, until/unless the externalities get applied to the price of coal.) Half the electricity in the US is generated by low-cost coal BTUs. Very few markets are predominantly fueled natural gas, but in acid-rain sensitve New England it comprises something like 1/3 of the total grid-source. In CT gas currently comprises ~20% of the base power generation source-BTUs, less than half the amount provided by nukes (the single largest source.) Oil-fired generatation is primarily (and very expensively) an island community artifact in that state, but there may still be some #2 peakers remaining on the mainland. Annually it's less than 20% of the total, but still far more than the national average. Nationwide oil is less than 2% of the grid-source.

Even in a 30% efficient all-gas-grid it would still be cheaper to heat hot water with electricity during non-space heating periods than with an 85% AFUE cast iron heating boiler for a single-family home. (The economics can change in larger multifamilies with a boiler dedicated for hot water heating.) The combustion efficiency can be pretty good, but the standby losses are horrific. Except for the smallest in the lineup newer highly insulated versions, internal heating coils in cast iron boilers run 25-40% efficiency in water-heating only mode. See: Units 1 and 12a in Table 2 p.7 (p12 in .pdf pagination) http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf

You may be able to make financial sense out of an indirect-fired tank though, if the boiler is at most 2x oversized for the space heating load, and heat-purging controls are used to cool the boiler down at the end of burns by dumping heat into the indirect (see unit #3 in the same table in that document.) A lot depends on how steep your electric rates are, ( CT electricity rates are among the highest in the lower 48) and how costly it would be to retrofit an indirect with the proper controls with a boiler. A bunch of pipe insulation (or even a drainwater heat recovery heat exchanger on the shower), can go a long way toward reducing HW heating costs with an electric tank, but less so with an oversized oil boiler with an internal coil, more than 60-75% cost using the boiler is all standby losses. (Drainwater heat recovery is subsidized by local utility rebates in some parts of Long Island, but SFAIK none in CT are doing so.)

How much oil do you burn over the summer when heaing loads are nonexistent? (It's ofetn hard to tell unless you top it off in mid-late May, and again in early-mid September.) If it's under 50 gallons swapping over might not be worth it, but I've seen a situtation in central MA where it was over 200gallons/summer for a family of 4 using the tankless coil. That family got religion or something and sprung for evacuated tube solar w/ electric backup, taking advantage of hefty state subsidies. But there are more cost-effective solutions than that, unless you're literally on one of those oil-fire island utilities with 40-50cent/kwh electric rates.