I work in real estate, doing for buildings and houses what surveyors do for boats and their buyers. So I have a little insight into furnaces, and by extension, boat heaters. After all, a boat heater is but a miniature furnace
Fuel is simply an energy source; fuel going into a heater/furnace has a specific energy content, measured in BTUs per: lb, gallon, litre, cu. ft. or cu. M, or what have you. The heater/furnace is designed to consume fuel at a nominal rate, measured in lbs, gallons, litres, cu. ft. or cu. M, etc, usually per hour. Specific energy content
times flow rate
gives the energy input per hour
. You can determine the specific energy content of your fuel of choice for comparison with other fuels. You can calculate how much fuel you need to consume in an hour to get a particular heat output (without regard for energy conversion efficiency - your actual consumption will be higher) Calculating your heat needs, though, is a whole, different animal!
Combustion isn’t 100 percent efficient; some unburned fuel escapes with the combustion products or gases. Conversion by the heat exchanger of heat energy in the flame to usable heat energy outside the furnace/heater is also not 100% efficient, the exhausted combustion gases aren’t at room temperature. If they were at room temperature a venting fan would be needed to draw them out of the combustion chamber; the fan becoming an energy charge against the system. The energy for the distribution fan in a forced air system should also be considered to get the overall energy picture.
In a domestic furnace an efficiency of about 90% to 92% is good and not expensive, and efficiency of about 96% is achievable with present technology (2011) but about twice as expensive. I never advise getting the 96% efficient furnace because the payback period from the savings in the gas cost is way too long to be worthwhile, at present natural gas prices. The 90% to 92% furnace pays for itself quite quickly if you're upgrading from say 65% efficiency.
So the heat energy equation becomes:
less lost energy from unburned fuel
less lost energy in hot combustion gas exhaust
= energy out
Fans have an energy cost but not in terms of the combustion fuel.
The efficiency of the heater/furnace is the energy input/energy output
times 100 percent. This number seems to be never
quoted by heater suppliers or manufacturers. It should be based on actual testing in accordance with specific standards.
It is somewhat of a cop-out to quote a rated heat output and a fuel consumption rate without a standard against which it is measured, although comparison between heaters can be made on the basis of fuel consumption for heaters rated at the same output
, and if you can trust the manufacturer's figures. But this won’t let you accurately compare a heater rated at 3,000 BTU per hour with one rated at say 4,000 BTU per hour.
Re the Platinum Cat Heater, as it's based on radiant heating, its effect is limited to line of sight, although possibly a water filled heat exchanger (copper tubes in front of the catalytic bed but not covering it totally, connected to a pump and radiator(s)…) could carry say half the heat output elsewhere, leading you to double the heater size...
Originally Posted by sailingdog
Somehow, I seriously doubt that they can vent all the combustion by products through a 1.5" hose
Modern furnaces of high efficiency have induced draft or pressure venting fans to exhaust combustion gases. The exhaust gases for a condensing furnace are nearly at room temperature and are typically piped with ABS plastic of about 1˝ inch diameter for a furnace with capacity of say 75,000
BTU or more. They are often sealed systems with inlet piping to bring in fresh combustion air from outside. Sealed systems are safer. I wouldn’t see any difficulty in handling the exhaust gases from a heater of say a tenth of that size with 1˝ inch diameter pipe and a properly sized exhaust blower, as the Platinum Cat Heater states it has.
In summary, and I hope this likely too lengthy explanation has been of some value,
- Fuel consumption rate comparison can only be made between heaters of the same rated output, and then only based on 'trusted' figures from the manufacturer.
- Manufacturers should provide efficiency figures, based on standard testing, for comparison purposes between brands and sizes of heater.
- You personal choice of heater is just that, your personal choice. There's no getting around it!
- and lastly, ALWAYS, ALWAYS have in the same compartment as the heater a battery operated CO detector, check the batteries regularly and change them as needed.