Cheaper to Operate: RV Propane Vented Furnace or Electric fireplace - RV-Dreams Community Forum

sdman · RV-Dreams Family Member

Cheaper to Operate: RV Propane Vented Furnace or Electric fireplace

flyone · RV-Dreams Family Member

I had pretty much the same question---but here is how I looked at it. If a gallon of propane cost 22 times less the kilowatt/hour rate than electricity then propane is cheaper, otherwise electric is cheaper. This is due to the number of BTUs in each. Example, propane is $3.00/gallon (approx. 91,000 Btu) and electricity is 11c per kilowatt-hour (22 kwh= approx. 91,000 Btu) then electric cost is $2.42 (22 times $.11) for the same amount of heating (BTUs) so use electric. Example number two, propane is $2.00/gallon and electric is 14c per kilowatt-hour, then the electric cost is $3.08, so use propane.

If the cost of one kilowatt hour is 22 or more times the cost of 1 gallon of propane (approx. the same heating value), use propane, if it is less use electric. At least this is how I looked at it and it makes sense to me at that (and this) time. Take it for what it's worth but I think the .14 cents per kwh is a little more expensive than the propane. .14x22=3.08 for the same 91,000 Btu's. At the rate of $2.42 for propane 1 kilowatt needs to be down to .11 cents to be equal. They both use a fan to move the heat so that works out even in my book.

Flyone

Sushidog · RV-Dreams Family Member

This assumes you are using resistance electrical heat producing only 3.413 BTU per watt hour of heat output. In other words, a 1500 watt electric resistance heater produces 5,120 BTUs of heat. A heat pump, however can be up to 6 times more efficient. For instance this high efficiency heat pump can produce 12,500 BTUs of heat from only 600 watts of electricity or 20.83 BTU/ watt hour for over 6 times the heat output for the same dollar of electricity consumed. www.geinnovations.net/Specifications.html

Now to be fair, that's a $2,000 heat pump, but it also provides cooling at a similar efficiency for money saving year round. So if the portion of you heating and cooling electric bill (assuming you are using only electricity for heating) is say $100/month, switching to this heap pump can save you around $84/month for a payback of slightly over 2 years. It's important to note that in severe cold (below freezing,) if it ever gets that cold where you winter over, you will need to use supplemental heat other than the heat pump, which can be used from around 38 degrees on up without its coils freezing up. Of course there are much cheaper, ($700-$1,000 range) 110v, slightly lower efficiency heat pumps (in the 15-17 SEER range) that are readily available. Some offer low temp kits that prevent the coils from freezing up, allowing you to operate them down to around 5 degrees, but consume a little energy doing so. Nevertheless, if you stay in weather this cold it will still produce electric heat far cheaper than a resistance heater will.

Chip

Terry and Jo · RV-Dreams Family Member

Without knowing where one might be living at the time, keep in mind that if one is in freezing temperatures outside, the gas furnaces may also provide heat for the underbelly, thus helping to prevent freeze-ups. If one's furnace doesn't heat the underbelly, then an additional electric heater will be needed.

We are in Colorado and temps have been as low as minus 6 degrees in the last month. While we are well insulated, if the outside temps get down to about zero degrees, our hot water line to the kitchen sink tends to freeze up. Everywhere else, the hot water lines are fine, so I need to direct some extra heat further back into the underbelly.

Not to make anyone jealous, but we are long term where we are, so we have leased a 120 gallon tank for our LPG. The LPG is delivered to the RV park where there are a total of 24 or 25 of us long terming over the winter. Our LPG costs us $1.80 per gallon. However, we did get one 40# cylinder filled and it cost us about $30.00. That one works out to just over $3.00 per gallon. We won't be doing that very much if we can help it.

Terry

Clay L · RV-Dreams Family Member

If you go HERE you can download a small program that will make the simple calculation for you.
It allows you to enter the appliance efficiency.

According to an email to me from engineering at Suburban Manufacturing, the efficiency of RV furnaces ranges from 70 to 80 percent. Water heaters are 70 percent on gas.

Note: Because Microsoft in their infinite wisdom didn't include the software to support the older help file formats, for Windows Vista and higher you will need to download and install a Microsoft program that allows you to use help files with the "hlp" extension for whatever operating system you are using.
You can download it Microsoft Knowledge Base. Scroll down to select your operating system.

-- Edited by Clay L on Tuesday 6th of January 2015 12:00:34 PM

-- Edited by Clay L on Tuesday 6th of January 2015 12:06:35 PM

-- Edited by Clay L on Tuesday 6th of January 2015 12:09:58 PM

sdman · RV-Dreams Family Member

flyone: Very good! You simplified it more than I did. This is more of an academic exercise for me as most of the time we are not that cold and not for very long. It is nice to know where the break even point is though.

I'm just running this through again below. Please let me know if I got this right!

It seems that you used an 80% efficiency for the furnace where I am using a 70% number. Anyway, 80% would give you the 22 times number and my 70% would give me close to 19 times. At 70% efficiency and $.14 kwh elect, then propane lower than $2.66/g would be cheaper to operate.

1g propane = 91,000btu @ .8 (80% furnace efficiency) = 72,800btu of heat energy

1kwh = 3412 btu.

72,800 (1g of propane)/3412 (1kwh elect) = 21.3 or ~ 22kwh elect for each gallon of propane.

So, if you know the cost of your electricity, mine at .14, then propane must less than 22 times the .14kwh of electricity ($3.08 per gallon) to be the cheaper energy source to use. If I use a less furnace efficiency number like 70% then the number would be 19 times the cost of electricity ($2.66/g) for propane to be cheaper to use.

Since 80% equals 22 times and 70% equals 19, I think I will use an even number of 20 that is easier to multiply and for me to remember!

sdman · RV-Dreams Family Member

Terry: Yup! Completely agree if you are in below freezing temperatures. We have a heated underbelly and would run the furnace if we got into that situation. So far in 2.5 years that has not happened. For us, if we get below freezing temperatures then we made a bad wrong turn somewhere

Chip: Heat pump would be a no brainer as far as it being cheaper to operate in the temperatures we are talking about (40 - 60). Too bad I don't have one.

Looks like we will have a run of temperatures in this range all day for a 2 week period. So with the fireplace running all day using an average of 1kwh (part time on low and high, 1500w and 750w) at .14 per kwh it would cost me around $50. If our calculations are right, running the furnace for this same time would cost me around $38 for the same heat. We aren't talking a lot of money here but it is sort of nice to know for peace of mind.

Neil and Connie · RV-Dreams Family Member

Terry and Jo wrote:
keep in mind that if one is in freezing temperatures outside

I can think of exactly zero reasons to be anywhere there are freezing temps outside☺

However the basic idea is right, if I was there for any reason then running the furnace helps keep pipes from freezing as you say, I just can't see any reason to do that.

Clay L · RV-Dreams Family Member

Neil and Connie wrote:
Terry and Jo wrote:
keep in mind that if one is in freezing temperatures outside
I can think of exactly zero reasons to be anywhere there are freezing temps outside☺
However the basic idea is right, if I was there for any reason then running the furnace helps keep pipes from freezing as you say, I just can't see any reason to do that.

I have to agree, but we had several occasions when we had to stay in freezing temps for a while. Most related to having to provide care for ailing parents and siblings.

flyone · RV-Dreams Family Member

sdman, looks like you got it. That is the way I see it --until someone comes along and shows me different I'm going to go with it.

Like you said we are talking about small differences here but it gives a little peace of mind when one doesn't have bigger real life issues to worry about.

Flyone

The Junkman · RV-Dreams Family Member

Posted over on the DRV fourm..

This is awesome..

www.eia.gov/tools/faqs/heatcalc.xls