1: Is the water heater a high efficiency type? The high efficiency one 
will not require a metal flue, but will have a plastic pipe flue and a 
matching combustion air intake to the outside. And there will be a 
condensate drain for the water condensed out of the exhaust as the 
products of combustion are cooled to something maybe 20F above ambient.
2: One of the components in calculating the efficiency is, there should 
be a name plate with BTU/hr. input and output. Efficiency % = 
Output/Input. This likely will be the overall efficiency unless the room 
gets warm. If it doesn't have a sealed combustion air inlet, then there 
probably should be a correction to account for incoming combustion air 
that needs to be heated. This air then likely is coming from leakage of 
the house at windows, doors, and other openings including less than 
perfect weatherstripping.

gacrowell@micron.com wrote:
> As far as the furnace goes, when we needed a new one, we coincidently
> needed a new water heater, and, I wanted to move both the water heater
> (from the laundry room) and the furnace (from the crawl space) to the
> garage.  One of the companies that I got quotes from suggested a water
> coil system.  Sounded interesting, and we've had it now for about five
> years with no problems.  There is no furnace, just an air handler with a
> hot water coil heat exchanger.  The only combustion is in the water
> heater that supplies both the domestic hot water and the water for
> heating.  The water heater is oversized slightly (I think we went from a
> 40 to a 50 gal.)  and is usually set at a normal temperature.  When the
> temps drop into the 30's it's usually necessary to bump up the water
> heater temp, sort of dial-a-btu.  Never had a problem with running out
> of domestic hot water, and the water temp is regulated by a tempering
> valve.  They -say- that the increased flow through the water heater
> actually increases its life; we'll see.  It's incredibly simple though,
> just the blower, coil, small pump, tempering valve, and the water heater
> we needed anyway.  Efficiency is hard to judge, since our old furnace
> was a piece of junk; gas costs did go down, comfort up, and so far no
> maintenance costs.  The air handler also has the A/C coils.  In Boise,
> ID.
>
> Gary
>
>   
>> -----Original Message-----
>> From: piclist-bounces@mit.edu 
>> [mailto:piclist-bounces@mit.edu] On Behalf Of William Couture
>> Sent: Wednesday, September 17, 2008 8:26 AM
>> To: Microcontroller discussion list - Public.
>> Subject: [OT] HVAC recommendations?
>>
>> Hi all,
>>
>> Well, our central air conditioner is dead.  The compressor is frozen.
>>
>> The system is 15+ years old, and the repairman says that it would be
>> best to just replace it (parts not available, Freon system).  
>> The entire
>> system would have to be replaced, as the new refrigerants operate at
>> higher presures.  Ballpark (not estimate) is about $3000.
>>
>> It is hooked into the heat system, which is gas.  It is from 1960,
>> and he thinks that putting a new AC into an old system wouldn't be
>> worth it.  New systems are much more efficient.  This brings the
>> ballpark figure to about $5000.
>>
>> Of course, one problem with new gas systems is the heat exchanger
>> -- we have a solid cast iron heat exchanger, and a pilot 
>> light.  The pilot
>> light keeps the temperature fluxuations down and keeps moisture out
>> of the sytem.  New systems do not have a good, solid heat exchanger,
>> and do not use a pilot light (thanks, government!) so they get
>> condensation and rust.  Lifetime is about 15 years, a little 
>> more if you
>> are lucky...
>>
>> So, what suggestions do people have for a new system?  What
>> brands should I be looking for, what should I avoid?
>>
>> Should I be looking at heat pumps instead of traditional systems?
>>
>> Anything else that I don't know that I don't know?
>>
>> And, in case it makes a difference, I am in Pennsylvania
>> (New England, the eastern coast) in the USA.
>>
>> Thanks,
>>    Bill
>>
>> -- 
>> Psst...  Hey, you... Buddy...  Want a kitten?  
>> straycatblues.petfinder.org
>> -- 
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>>     
>
>   
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