[Greenbuilding] Opinions on electric tankless HW heaters?

[Bob Waldrop]

Probably we were using that much.  At that time we our household had 
increased temporarily by the addition of 2 teenagers, 2 adults, and 2 
smaller kids, all of whom seemed to like long showers.  IIRC, one of my 
reasons for turning the heater on and leaving it on was to see what the bill 
would be like for a more conventional household (the additional folks living 
with us had not been habituated to our lower level of energy consumption). 
So maybe its not completely apples to apples with our present lifestyle 5 
instead of 8, with all 5 (one of whom is age 5 going on 15 today) having 
become habituated over time to being frugal with energy.

We already have a blanket around the heater.  I've never been able to test 
how long it takes to cool to the ambient temperature by itself without 
withdrawing hot water and adding cold water.

Bob Waldrop, Okie City

-----Original Message----- 
From: Paul Eldridge
Sent: Friday, April 22, 2011 8:27 AM
To: greenbuilding at lists.bioenergylists.org
Subject: Re: [Greenbuilding] Opinions on electric tankless HW heaters?

Hi Bob,

You mentioned that your electricity consumption increased by more than a 
thousand kWh per month when you operated your electric water heater 
continuously, which suggests a hot water demand in excess of 33.0 kWh per 
day.  The Energy Factor rating for a newer, conventional model would be in 
the range of 0.92 to 0.94, which means the standby losses are roughly equal 
to that of a 40-watt light bulb, or less than 30.0 kWh/month.  [Note that if 
you were to add an insulating blanket, you could probably cut that by a 
third or more, but first check with the manufacturer to ensure this won't 
void your warranty.]  After subtracting these standby losses, some 970+ kWh 
would be attributable to water heating; assuming an inlet temperature of 10C 
and a supply temperature of 50C, that's roughly 180 gallons or three and a 
half tank's worth of hot water demand per day.  Are you sure you were using 
this amount of hot water?
+--------------------------------------------------------------------+
We use to heat our DHW with oil (there's no natural gas service in our area) 
and have since switched to electric.  We installed a small, 70-litre, 
115-volt, 1.38 kW model that is plugged into a Kill-a-watt power monitor. 
Our two person household averages a little less than 5.0 kWh per day, 
including standby losses, and we both shower daily, wash clothes in hot 
water and operate the dishwasher twice a week.  We've made a concious 
decision to wean ourselves off fossil fuels to the greatest extent possible, 
and as part of this purchase 12,000 kWh/year of 100 per cent renewable 
energy through Bullfrog Power.  That $20.00 a month effectively offsets 115 
per cent of our home's total energy needs, i.e., space heating (ductless 
heat pumps), DHW, cooking (induction), lighting, appliances and plug loads. 
>From our perspective, electricity is our best option.

Cheers,
Paul

----- Quote -----
  We put in an off the shelf mid-price electric water heater, and added an 
on off switch, so most of the time it is off and we turn it on maybe twice a 
week.  People periodically tell me that that doesn't save any energy, for 
various reasons, and while it is true that I am not a scientist. . . as an 
experiment we left it on 24/7 a couple of months in the fall when it wasn't 
especially hot or cold and our bill went up over a hundred dollars each 
month (more than a thousand kilowatt hours) so I would say that the simple 
on off switch does in fact save energy. Not to mention giving my poor frugal 
heart pains when I opened the bill. The plan when we get more money is to 
add a solar water heater.

   Bob Waldrop, Oklahoma City




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