[Greenbuilding] tankless water heater efficiency...

[Frank Flynn]

The "instant hot" of the tankless is a significant advantage.

Although 'loss' at the water heater might be small (no doubt this is  
where EPA is measuring it)- loss through the pipes in your house can  
be significant.  So you must insulate the hot water pipes - but even  
so they still loose heat; first thing in the morning the hot water  
isn't hot for a while as the how water must travel through the pipe  
and warm it up.  Depending on your house it could be significant.

Even if all that heat lost from your pipes is inside your living  
space and you can argue that your furnace won't have to work as hard  
now - the water is lost as good clean water goes down the drain.   
This is more of an issues someplace than others but I live in a semi  
arid area (California) -- remember water is the new oil...

You can recirculate this cooled hot water and pump it back to the hot  
water heater to be reused but this requires a third pipe.   I've seen  
(but not used) a system that just pumps the cooled hot water back  
into the cold water line there at the remote sink or shower.  An  
interesting idea and much simpler than running a third water line but  
somehow I wonder if you don't wind up with both hot and cold being  
tepid.

Or (money no object) go with solar hot water and recirculate because  
if it was solar heated who cares if you loose some heat (it was  
'free' after all) and use small tankless boosters - either one for  
the whole house or several, one at each water use location.  These  
heaters can be smaller than you'd normally need without the solar and  
they would be off most of the time because the Sun did most of the  
work for you.

Good luck,
Frank

On Dec 21, 2006, at 12:58 PM, Kidd, Peter wrote:

>
>> Electric storage heaters look good here, producing 95% of their  
>> energy
> input.
>> How much can a tankless improve that? Are any tankless units more
> efficient?
>
>> Nick
>
> Electric tankless have slight standby losses, but the improvement over
> 95% is slight regardless.  More to the point, with electric in
> particular, much of that standby "loss" isn't loss in the half of  
> North
> America that locates hot water heating appliances inside.  The loss is
> just space heat, so even considering fuel price and control issues,  
> it's
> still not all "loss", for an effectively higher efficiency.  I'd  
> like to
> measure the (positive) impact of this on the performance of a GFX,
> possibly slightly modified for capturing more batch flow heat (or has
> someone already measured this?).
>
>
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