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PostPosted: Sun Feb 19, 2012 11:09 pm 
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keydiver wrote:
I think part of the confusion is that I was comparing it to a standard electric hot water heater, a little off topic,sorry. A typical electric hot water heater uses $500+ per year in electricity, so the payback for solar hot water is very short.

Is it really, though? Even at $500/year and if it costs $5k to install you're looking at 10 year break-even which is similar to PV these days.

But for my house, we only use about 6 therms / mo for non-heating months (only gas use is for water heater and HVAC) which is like $7-8/mo or ~$100/year. This is with a standard water heater. I'd have a very hard time justifying a 50-year payoff when the system will probably need to be replaced at least once in that time. Never mind that I'll still have a gas bill unless solar hot water systems are good enough to store enough hot water for showers in the morning. (Would have to find room for a tank - I guess with the tankless heater I'd have room)

Or I could spend $5k on 1.5 kW of PV (after rebates) that will generate about 2000 kWh/year. With 1 therm of gas having about 30 kWh of heating, that's 66 therms equivalent - enough to power a resistance electric water heater of similar efficiency to the current heater - or with a hybrid water heater that would leave me with well over 1000 excess kWh/year to drive the LEAF. Or do the tankless high efficiency hot water heater and don't worry about the minimal amount of gas the house uses - one of the tankless units would probably cut my gas usage by 30-50% compared to my current heater.

Electricity at a retail price of $0.14/kWh the same $5000 investment has the potential to save a lot more money - 2000 kWh is about $280 worth compared to under $100 for 60-70 therms of natural gas.

Obviously the amount of hot water one uses plays a big role here - conservation is probably the biggest winner here - install those low-flow shower heads!

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PostPosted: Mon Feb 20, 2012 12:01 am 
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Delivery Date: 29 Apr 2011
Leaf Number: 850
EVDRIVER wrote:
Anything electric for primary hot water is an energy pig...


I haven't broken it down to therms vs kWh's but today's electric hot water heaters have come a long way. The leading resistive electric hot water heaters
now reach somewhere in the 90% efficiency range. The hybrid electric heat pump goes way beyond that, the one I went with is rated at over 200% efficiency, in other words it's off the charts compared to traditional electric hot water heaters. The cost of going gas or electric tankless was going to be much more expensive than going hybrid electric/electric heat pump because it could be installed without any changes to our breaker box and of course no additional gas line hook up, it simply took the place of the old resistive heater. Adding solar hot water would have been prohibitively expensive for the minimal additional savings. to make back the extra money we would have had to spend would have taken many many years for either gas or electric tankless or a solar combo option. I won't know till I see a few utility bills, but we are likely to see our hot water bill drop to around $10 a month with the electric hybrid heat pump... the utility is no longer offering rebates on any other water heater accept the heat pump. Like anything, one has to properly assess if it can meet their needs, but so far it seems very promising for our application.

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PostPosted: Tue Feb 21, 2012 4:13 pm 
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I'd like to second the vote for the hybrid electric hot water heater.. We've had ours installed for over a year now (installed just the month before we got our LEAF) and can't say we've had any complaints. Though it did cost a bit to buy the unit and get our electrical squared away, we saved some by running the new wires through the same conduit as the L2 charger wires.

In my mind, the advantages of the hybrid are several: 1) further reduced our fossil fuel use, 2) no flue up which heat gets exhausted (true for both conventional and tankless gas water heaters), 3) not creating heat, just transferring it, 4) rebates and tax credits. Cost wise, coming from a conventional gas heater, I've got to admit that the hybrid is a bit closer to a wash than I'd have liked, but that's mainly because it gets a bit too cold here in Washington during the winter for the unit to run in heat pump mode; during the summertime the electricity usage goes way down as there's plenty of heat to shuffle from the garage air into the water. To give some numbers, as best as I can recall, old usage was roughly 1 therm/day; new usage averages roughly 150kWh/month.

On the downside, our combo water heater/furnace exhaust stack now constantly drains condensation on cold days as there is no longer a constant supply of hot air moving up the stack... :-(


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PostPosted: Tue Feb 21, 2012 6:33 pm 
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There are gas units that are 95% efficient, that is why they can use PVC venting, because of the low heat loss. Gas is far less costly than electricity in many places, in SF it is a big difference.

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PostPosted: Wed Feb 22, 2012 1:17 am 
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Delivery Date: 29 Apr 2011
Leaf Number: 850
yeah, that is higher than the best standard electric water heater I found. the highest rating I saw was .93 but the hybrid electric heat pump heater is rated at over 2.0 in hybrid mode and even higher in pure heat pump mode, more than double standard gas or electric heaters. with more than double the efficiency, it just wasn't cost effective to go tankless in this market, I was surprised.

EVDRIVER wrote:
There are gas units that are 95% efficient, that is why they can use PVC venting, because of the low heat loss. Gas is far less costly than electricity in many places, in SF it is a big difference.

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PostPosted: Thu Feb 23, 2012 10:49 pm 
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GaslessInSeattle wrote:
yeah, that is higher than the best standard electric water heater I found. the highest rating I saw was .93 but the hybrid electric heat pump heater is rated at over 2.0 in hybrid mode and even higher in pure heat pump mode, more than double standard gas or electric heaters. with more than double the efficiency, it just wasn't cost effective to go tankless in this market, I was surprised.

Keep in mind that while hybrid water heaters can have an efficiency > 1 (typically just over 2), the overall efficiency depends highly on the efficiency of the power plants supplying your electricity.

Basically - unless your local grid (obviously in Seattle you are mostly hydro so electricity always wins), is > 50% efficient using a high efficiency tankless will be more efficient than a hybrid water heater. And if you live where it gets cold, the hybrid will lose efficiency, too.

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PostPosted: Thu Feb 23, 2012 11:25 pm 
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Leaf Number: 850
drees wrote:
... Basically - unless your local grid (obviously in Seattle you are mostly hydro so electricity always wins), is > 50% efficient using a high efficiency tankless will be more efficient than a hybrid water heater. And if you live where it gets cold, the hybrid will lose efficiency, too.


From the reading I've done so far, it seems to depend significantly on what mode the hybrid is set to. We've got it in pure heat pump mode and it's in our basement, sheltered from cold. It's hardly using any energy. even if it were getting juice from a 50% efficient power plant rather than our 100% renewable offset through the utility company, the ROI from a gas set up would be half a lifetime compared to the hybrid's just a few years. Any time we have more demand than it can keep up with we can switch it to hybrid mode and rely on the resistive coils, like when relatives visit. It's not for everyone, but it's cutting edge!

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PostPosted: Wed Feb 29, 2012 6:51 pm 
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i had an electric tankless, it worked, but could only do 1 shower at a time.


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PostPosted: Thu Mar 01, 2012 6:00 pm 
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toasty wrote:
i had an electric tankless, it worked, but could only do 1 shower at a time.

Good to know. I've never been able to run fast enough to take two showers at the same time. :P ;)

I had on-demand gas units in Germany and loved them - simultaneous showers, dishwasher running, etc. - no worries. My only experience with this in the 'States is standard gas/electric heaters, and three days with an on-demand gas unit and solar heating. I brought my 9 year old son with me on the Earthship trip specifically to test the hot water system.

The system uses one SunEarth EP-32 4x8' collector, a small 12V PV panel to run the circulation motor (12VDC Ivan Labs pump), a 40 gallon boiler storage tank, and has a Rinnai V53 on-demand gas backup unit. After a 15 degree overnight and morning showers we had 90 degree water in the storage tank. Once the sun came over the mountains and started the circulation pump, it only took about 30 minutes for the storage tank to hit 140 degrees again.

The backup unit, when it ran, was quiet and very fast. (The only thing we heard when the Rinnai started was the (?) exhaust fan for exhaust. The units we had in Germany sounded like a furnace starting up - whoosh! That was in the early 1990s though...) We could run all the hot water in the house day or night and didn't run out, even though the 40 gallon storage tank is smaller than my home hot water heater (I like long hot showers - and did I mention I brought my 9 year old? :lol: ). It sold me!

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