# What would be the hourly cost of LP to run my fireplace vs. running my LP furnace?



## thz123 (Jan 25, 2010)

I have contracted my LP price at $1.21 per gallon. 
92,000 btu per gallon of propane.

LP Fireplace is 21,000 btu on high 
(21,000/92,000=.2283 of a gallon per hour x $1.21 per gal.=.2762 cents per hour on high)
Is that the correct cost per hour (.2762 cents)?

LP furnace - 75,000 btu
(75,000/92,000=.8153 of a gallon per hour x $1.21 per gal. = .9865 cents per hour)
Is that the correct cost per hour (.9865 cents per hour)?

Thanks for the help.


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## DAKSY (Jan 25, 2010)

thz123 said:
			
		

> I have contracted my LP price at $1.21 per gallon.
> 92,000 btu per gallon of propane.
> 
> LP Fireplace is 21,000 btu on high
> ...



Close enuff. There are actually about 91.5 K BTU per gallon of LP, 
but what's 500 BTU between friends?
Most people do the math the other way to determine how long it'll take
to burn a gallon, based on your BTU input.
What it boils down to is whether or not you can heat an area (space heat)
comfortably enuff to leave your furnace off.
If you can, you already did the math....


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## thz123 (Jan 25, 2010)

Thank You for the input. The way my house is laid out, I can heat my living room, kitchen, and dining room with just the fireplace. Leaving the furnace off. At night and when I am away during the day the furnace will be on. I just wanted to figure which way was the cheapest heat cost.


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## Later (Jan 25, 2010)

The furnace doesn't run continually like the fireplace does so the savings might not be as great as they appear.


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## DAKSY (Jan 25, 2010)

Retired Guy said:
			
		

> The furnace doesn't run continually like the fireplace does so the savings might not be as great as they appear.



Not so Grasshoppah! 
The fireplace can be run off a t-stat as well, 
so there CAN be substantial savings...


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## KeepItNatural (Jan 25, 2010)

interesting...
what are you spending now per month in the winter to heat the house?


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## SteveT (Jan 26, 2010)

No matter how you heat your house , it is heat loss that determines how much fuel is consumed. Your approach makes sense as you are lessening the total heat loss by only heating part of it during the day. Effectively, with the "fireplace only" you have two zones and are only heating one.

As your math shows, the fireplace is about 23% the capacity of the furnace so it burns fuel at that ratio (assuming equal efficiency). Do the rooms you can heat with the fireplace (living room, kitchen, and dining room) realistically account for 23% of the heat loss of the entire house? 

If so, you will use 23% as much propane. If not, the fireplace will be running more than the furnace so the savings will be less than the ratio of fireplace/heater capacity. DAKSY is correct -- you can put a t-stat on the fireplace so it doesn't run full time. But a lower capacity device on a t-stat will run more than a larger capacity device on a t-stat heating the same area.

If I was to take a shot at the savings, I'd ratio the areas of the floor space you are heating vs. not heating -- if you are heating half the house you'll use half the fuel. You can refine this with more precise data (like is there a picture window in one area, difference in insulation due to an addition, or whatever).

But using ratios of heater sizes doesn't work, IMHO.


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## Fsappo (Jan 26, 2010)

If by zone heating you can be happy with the heat a gas fireplace gives you during the day and just run the furnace at night for the bedrooms, you'll end up using less LP.  How much less is hard to figure out.  $1.21 per gallon for propane is VERY cheap..at keast from what I have seen here in NY.


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## Highbeam (Jan 26, 2010)

Whoa, don't forget about duct losses. This can be a huge percentage of loss when compared to a hearth appliance.


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## Fsappo (Jan 27, 2010)

Highbeam said:
			
		

> Whoa, don't forget about duct losses. This can be a huge percentage of loss when compared to a hearth appliance.



+1 yup, forgot about that


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## thz123 (Jan 27, 2010)

I just bought the house, it is 4 years old. With Anderson Windows, insulated 2x4 walls to R13 I think, plus the r-factor for the wall material. The Ceiling has R32. The main level is 1650 square feet, 3 bedroom walk out ranch. I have a Quadrafire Castile pellet stove in the basement, which I only run when I am home (5pm to 6am). I only run the LP fireplace from 5pm to 8pm. I have my furnace set at 58 from9pm till 5am when it is set for 66. At 6:15 am it goes back down to 58. The furnace is 93%, and 75,000 btu. I just had the furnace cleaned and tuned. I have one other LP appliance and that is the hot water heater.

So, all I am trying to do is figure out the way to heat the home, while using the LP fuel in an economical way. Thank You for the help.


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