Demand heater for SHW backup [RE-wrenches]

[Travis Creswell]

We've used tanked propane water heaters in low load radiant in floor
applications and domestic water heating. They were the power vent style
models with an electronically controlled igniter so no standing pilot light.
Plus a damper built into the power vent that automatically closed when the
burner wasn't firing which would help with draft losses and tighten up the
building envelope.  These models are readily available locally and
reasonably priced (less then $600 the last time we bought one).  Energy
factor on these units is in the low to upper 60's. Not the greatest but they
do everything else so well.

Regarding tanked units heating up the tanks thus leaving nothing for the
solar to do is easily and effectively handled.  With a standard electric
water heater you put a timer 240v timer on it to prevent from getting
electricity during the day time and preferably a small window in the night.
The same can be done with the propane power vent unit instead you use a
simple 120v plug in timer.  In both cases you must coach the customer to be
proactive about managing their hot water usage.  Just using delay timers
that are built into most dishwashers and clothes washer is tremendously
effective.  Many of our customers turn the breakers off to their water
heaters in the early spring then back on later in the fall after their 2nd
or 3rd luke warm shower.

We are not fans of tank less water heaters.  We've had too many reliability
and customer usage problems with them.  I'm totally confident that if you
looked at the total 10 or 20 year cost of ownership of a tankless unit vs.
standard unit the tankless would loose.

Just my 2 cents.

Travis Creswell
Ozark Energy Services

-----Original Message-----
From: Todd Cory, Mt. Shasta Energy Services
[mailto:toddcory at finestplanet.com] 
Sent: Tuesday, August 21, 2007 7:21 PM
To: RE-wrenches at topica.com
Subject: Re: Demand heater for SHW backup [RE-wrenches]


This is true, the standby losses (up to 40%) on a tank style gas water 
heater are horrible. The whole time the unit is not heating, the 
convection up the center flue is cooling the tank. I am surprised no one 
ever came up with an automated draft blocker on these units.

Todd



Tom Lane wrote:

>
> Only on demand gas water heaters save money about 20% versus low end 
> gas water. heaters   gator tom
> ----- Original Message ----- From: "Todd Cory, Mt. Shasta Energy 
> Services" <toddcory at finestplanet.com>
> To: <RE-wrenches at topica.com>
> Sent: Tuesday, August 21, 2007 8:10 AM
> Subject: Re: Demand heater for SHW backup [RE-wrenches]
>
>
>>
>> While everyone thinks demand heaters are oh-so-efficient, in all 
>> honesty they really do not save much energy. If you have a SDHW 
>> system, you already have a tank... so super insulate that and use the 
>> top element as your (electric) back up. Propane demand units for 
>> backup are prone to freezing, scaling and not 100% efficient like an 
>> electric unit is. If you must use one of these things, electric is 
>> the way to go but be warned the current draw is huge.
>>
>> Todd
>


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