Spa Heater Efficiency?

[cygnusecks]

Gas co. was out today hooking up the propane tank to the heater. While they were testing it, I was asking questions and observing. I observed that the vent was putting out REALLY HOT air. So hot that if I had placed my hand right over the opening, I think I would have seriously burned my hand. I asked the tech about this, saying that it felt like a lot of heat was being lost (i.e. low efficiency). He confirmed this, saying that most pool/spa heaters run in the 50-60% efficiency range *by design*. He said that the more efficient your heater is, the more internal condensation that forms as a result of the heating, and it wears out internal parts fast. He said that heaters that are in the 80-90% efficiency range don't last more than a few years before needing replacement parts, etc.

Is this guy full of crap? I can't believe that half of my propane is being used to heat up my neighborhood instead of my pool! Surely all that much lost heat could be used for something.

FYI This is a Jandy LX 400kBTU heater. The URL below says it operates "up to 83% efficiency". I don't see how it's possible to be that efficient, with so much heat coming out of the vent.

http://www.jandy.com/html/products/h...lxlt/index.php

[Poconos]

Don't confuse temperature with heat. Yes the stack gas is hot but efficiency is based on heat. One measure of heat is the BTU or British Thermal Unit which is the amount of heat needed to raise 1 pound of water 1 deg F. Since air is a lot less dense than water the little bit of heat out the stack will raise it's temperature a lot more than the water in the heat exchanger. Don't know about pool heaters but the condensation statement is real to some extent. One combustion product, water vapor, will condense on a cool surface and if the efficiency gets real high you run the risk of condensate forming and possibly damaging the heat exchanger or other components. In the high efficiency home furnaces I believe the combustion air flow is so low it has to be assisted with a fan and directed to a final heat exchanger made of stainless steel to handle the condensate. Never had one but that's what I learned years ago from someone that had one.
Hope this helps.
Al