BTU/hr converison to kilo Watt 2

[saab007]

How does BTU per hour equate when converted to kiloWatt? If say you have a gas fire place at a certain BTU/hr - can you compare that to the kilo Watt of an electrical heater as far as power outage ??

Thanks in advance.

 

[IRstuff]

BTU/hr = 0.293 W

TTFN

 

[macmet]

try downloading convert.exe by josh madison.

 

[25362]

Btu/h is a measure of power, equals 0.2931 W (as IRstuff indicated).

1 W = 1 J/s = 1 N.m/s = 1 kg.m²/s³

 

[katmar]

The simple conversion from BTU/h to kW is one thing, but I suspect that what saab007 is really asking is whether a fire place of a given power compares with an electrical heater of the same rated power (once converted from kW to BTU/h).

The rating on the gas fire is likely to be the quantity of gas burnt. Similarly, the electrical heater will be rated in terms of the electricity consumed. What you need to check is the quantity and temperature of the air that goes up the chimney of the gas heater. This will be a loss of heat, and would mean that the gas heater is delivering less heat into the room than the rated value.

Of course, if you are using one of those small self contained gas heaters where there is no external chimney then all the heat is retained in the room and in my opinion the gas and electrically driven units would be comparable in efficiency.

 

[tombmech]

Re-reading your question, it sounds like you want to compare a gas fireplace with an electric heater. In other words, place a radiant electric heater next to a gas fireplace - how do they compare: heat vs. energy?

BTW, I always think in terms of 3.41 Btuh = 1 Watt (the reciprocal of the conversion posted above).

You may use the conversion, as long as you're comparing electricity in Watts to Btuh's in fuel burned (NG). Natural Gas is sold in units of Therms (100,000 Btuh), and has an effective specific heat of combustion of 1000 Btuh per cu. ft. You may be able to derive the number of therms or Btuh's burned by watching your gas bill + fireplace burn time, or perhaps the gas fireplace mfr has a fuel consumption rating.

Efficiency is the important factor, though. A radiant electric heater may approach 100% efficiency - Watts of electricity into the electric heater equals Btuh's of heat output. However, a common fireplace - even one with natural gas - is horribly inefficient: on the order of 10%. Without a heat exchanger to transfer the convective heat, most of the heat generated from burning the Natural Gas goes right up the chimney. What's left to heat the space is only radiation from the flame.

Even so, the 100% efficiency of a radiant electric heater pales in comparison to the COP of a heat pump. (In fact, it could be described as a salesman's trick.) Heat pumps use the rejected heat from trying to air condition the infinite sink of outdoor air. COP's with heat outputs of 3 times the electric power input are common.

 

[quark]

Good comments by both katmar and tombmech. I particularly appreciate tombmech's comments on thermodynamic wastage of energy either by direct burning of the fuel or electric heaters as well.

The same issue was initially raised by Lord Kelvin about 100 years back. He proved that when a heat engine and a heat pump were run in combination, we could be able to get as high COP as 6. Though electric heaters are 100% efficient, heat pumps are better choice as far as operating costs are concerned.

As katmar stated, electric heaters will give better advantage over fuel burning as lot of energy is wasted via flue gases. Stars to both the members.

 

[saab007]

Thank you all for your comments. I realized my question was slighlty unclear only after I posted it. Like Katmar mentioned I was trying to understand the conversion of Btuh to kW - even though I have a little tool to convert the units - I was not sure if that was the total picture or if there were any other factors that needed to be considered. Tombmech - my next step is to look in to the efficiency of gas vs electricital heaters and then cost association per heat provided (temp change per fixed ambient temp).

Just to let you know I am helping my nephew in his science project regarding effective heating appliance and he wants to compare comparable rated electrical and gas heaters.

Thanks again.

 

[tombmech]

Interesting. I envy your nephew these days - wish some of mine were "science projects." ;-)

Some other interesting points - if you are talking real gas heaters instead of fireplaces, and comparing them to electric heat, the cost difference is a simple calculation in fuel cost vs. efficiency. However, there are definite comfort preferences.

Gas heat is much more forgiving with humidity. Typical gas heat will burn so cleanly that venting is not needed. The products of combustion are water vapor, so gas heating has a built-in comfort advantage in that dehumidification does not occur as readily. Electric heat can feel uncomfortably dry by comparison.

Electric heat is almost always directly exposed to the airstream. This causes several bad effects. The coils will burn out after a period of time - similar to a light bulb filament. Also, dust in the airstream collects on the elements. Winter startup after the cooling system is often accompanied by a burning smell that permeates the space.

Of course, as mentioned above, "efficiency" has limited meaning regarding heat with heat pumps. My former professors would frown on this statement, but COP's are like having 200, 300, or 400% efficiency and so on. They have disadvantages too, though.

 

[sathanasiou]

For any conversions try downloading "Convert" from

http://www.joshmadison.com/software/

 

[ddkm]

On units alone, Btu/hr is the exact equivalent of kW in the SI environment.

Purely for conversion purposes, you can do as follows:

1 J = 9.48 x 10^-4 Btu (taken from many conversion tables)

Thus:

1 Btu/hr = (1/9.48e-4)J / (3600s)
= 0.293015 J/s
= 0.293015 W
= 0.000293 kW

======================================================

With regard to comparison power ratings between the different heating equipment, it is more than just conversion of units, as others have mentioned here.

---engineering your life---

 

[rmw]

Caution:

There are more products of combustion from a gas heater than just water vapor. If there is complete combustion, there is always CO2, and as O2 is depleted by the combustion process, or, if there are problems of any sort with the burner resulting in incomplete combustion, there is always the danger of CO, a known killer.

In the old drafty house(s) that I was raised in, open gas heaters were the norm. But there was enough ambient air leakage into the house that we didn't die.

However, in modern homes built to different standards, they may be tight enough so that open flame gas heaters could be dangerous.

Maybe your nephew could include a portion of his project to this aspect of gas heating.

rmw

 

[GenB]

Nat gas at effs. of about 60% is used to produce the electrical power
so when the ele. energy get to your house already has a disadvantage - more expensive- new gas fired equipment can accomplish up to 85-95% effs, ele. aparatus at 98 - 100% effs.
the bottom line is that electrical energy is 25 to 40% higher than nat. gas even at the hi-effs, of electrical power, aplications are secundary and pay to take in consideration,
gas fired equipment takes more money to install in most of the cases.
genb

 

[tombmech]

rmw:
You raise a very important point. CO detectors should always be standard equipment in a gas-heated (or fireplace) residence. Open flames within the conditioned space are obvious suspects. However, even with a gas furnace using heat exchanger separated flame, and located outside of the conditioned space - there is potential danger. Heat exchangers will crack over time, and the products of combustion will leak into the conditioned airstream.