COMMUNITY FORUM

johncdjr1207

10:29AM | 12/01/07
Member Since: 11/23/07
15 lifetime posts
Bvhvac
Hope some one can answer this.

I've figured out how to compare the cost per BTU of propane versus electrical heat.

Now for the heat pump. The best I can find has to do with the coefficient of performance (COP). I've found a statement that todays heat pumps have a COP between 2 and 5.

Is it correct to understand then that for each BTU of electricity that goes into a heat pump, it puts out twice as many BTU if it is rated as a COP of 2, three as many if COP of 3 etc.?

Help me understand this.

I understand the SEER rating part.

johncdjr1207

08:05AM | 12/02/07
Member Since: 11/23/07
15 lifetime posts
Then my next question is:

If my propane cost $22.40 per million btu (at 91500 btu per gal, cost of $2.05/gal) and my electricity cost $35.50 per million btu (3,414btu/kw at cost of .1214099/) then divide the cost of elect by 2 as the heat pump gives me 2 times the btu per btu consumed, then my elect cost drops to $17.75 per million btu released or removed from/into the house. Assuming the inside unit is 100 percent efficient.

Somewhere in there, it must be something having to do with the outside temperature.

Where am I off on this?

Don't take it that I am arguing on this. I am trying to understand something I know very little about.

johncdjr1207

05:17PM | 12/02/07
Member Since: 11/23/07
15 lifetime posts
I guess my basic question is: If propane cost 2.05/gal and electricity cost .1214099/kw, then which is going to be the cheapest way to heat my house this winter?

The propane is used in a none-externally vented heater( I know your opinions regarding these) and the electricity I use is in a heat pump with a SEER of 13.

I haven't figured out a way to compute the comparison.

johncdjr1207

06:16AM | 12/03/07
Member Since: 11/23/07
15 lifetime posts
Ok, I think that even I can understand that.

For the same amount of heat it is costing me $2.05 if supplied by propane and $1.30 if provided by electricity.

One last question and I'll leave you alone.

I've read that propane burns/delivers its' Btuh at 99.9 % efficiency (if not vented as in my case). If I substitute that into the calculation, it gives me a cost comparison of $3.27 divided by 2 or $1.63 (25% more economical) for the electricity. Which is still much in favor of the heat pump/electric set up (as long as the resister strips don't cut in).

If the above is correct in your opinion, no need to answer. Thanks much for the assistance.

johncdjr1207

08:39AM | 12/03/07
Member Since: 11/23/07
15 lifetime posts
Thanks. You almost dazzled me with your foot work when you said:"the efficiency of the vented and non-vented combustion is the same".

But I thought for a while. Yes, the combustion (freeing the Btuhs) is the same. The furnace efficiency is how much of that is sent into the house vs how much is released up the flue/vent/.

As for the dangers of the non-vented burners--I've lived dangerously on the edge all of my life. Why, I even drove on the interstate in Dallas/Fort Worth at go to work and go home times!!! Talk about placing your life in danger!!!!

Thanks for all the help. I've learned much from our discussion.
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