[Greenbuilding] Hot Water Heater options

[Keith Winston]

Hi Bambi! Your choices (as if you didn't know):

Hi-eff. gas tank unit, 90+% combustion eff., standby loss takes system 
efficiency probably 10-20% lower, $600-$3000
Elect. tank unit, nearly 100% eff (though electrical generation is only 
35% or so), somewhat lower standby loss (no flue), $250-500
Gas Tankless, no standby loss, combustion efficiency 85%, $1000-2500 
(flow delays and capacity limitations are occasional complaints with 
tankless/on-demand heaters)
Electric tankless, nearly 100% efficient, same generation caveat, no 
standby loss, $4-600 (same flow-delay caveat, also they require a BIG 
electrical circuit)
Heat Pump Water Heater, probably > 200% efficient BUT uses indoor air so 
gives you free AC in the summer BUT adds heating demand in the winter, 
must be coupled with tank (some units include tanks), probably 
$1200-2000 installed (Watt$aver has mixed reviews, includes tank, trade 
price around $1300: Nyletherm 110 has somewhat more complicated install 
& requires additional tank, unit price around $900 
http://www.nyletherm.com/waterheating.htm)

Ah, and of course, SOLAR. Good fit with any tankless, potentially good 
fit with tanked backup systems. Federal tax credits. System cost, before 
fed & state credits, $5-8000. Efficiency through the roof in a good 
install in a favorable location.

Finally: if all your fixtures are within 20 feet of each other, they 
probably all go down the same stack? Are they all out of the basement, 
that is (particularly) is your washing machine somewhere other than the 
basement? It is quite likely that installing a gravity film exchanger on 
your waste stack is a no-brainer with every system above. Installed cost 
something like $1000, requires 3-5' of vertical stack, with as many 
fixtures flowing through that section of stack as possible. 
http://gfxtechnology.com/

I don't stand by a single number above! This is all off the top of my 
head, so it might help orient you/others, but I don't guarantee anything 
here is accurate! Specifically, I await all kinds of arguments about the 
real level of standby loss a modern, well-insulated tank system suffers.

We'll leave geothermal out of the picture for now? Of course, someone 
ought to have built a mini-split Air to Water unit, but it's not out 
yet. Good luck, see you soon!

BTW: have there been 3-4 people living there, and how has the 40 gallon 
tank stood up -- any shortage of water? This will help size the next unit.

Keith


Bambi Tran wrote:
> I'm trying to figure out the energy-efficient, and life-cycle cost-effective hot water heating option for the following affordable rehab project... please advise!
>    
>   -- 1000 sf rowhouse in Washington, DC
>   -- 3-4 people
>   -- 1 full bath, 1 half bath, laundry (washer/dryer), kitchen with dishwasher and sink... all within 20 feet of each other
>   -- available utilities: gas, electric
>   -- mechanical room in unfinished cellar
>   -- current water heater is an old (1980s), 40 gal, gas water heater
>    
>   Cheers,
>   Bambi Tran
>
>  		
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-- 
Keith Winston
Earth Sun Energy Systems
3927 Madison St.
Hyattsville, MD 20781
301-980-6325
keith at earthsunenergy.com
www.EarthSunEnergy.com