RV LP Furnace Efficiency?

[sidney]

I'm trying to find the actual efficiency rating of our Suburban RV furnace... but so far have found no published specifications.

Anyone have the real world efficiency rating of the typical RV LP furnace... I'm guessing 70 to 75%.

I'm trying to compare the cost of electric heat at 13 cents per kilowatt hour vs LP at $2.79/gallon and assuming 75% efficiency.

Using the link below... LP @ 2.79/gal vs 13 cents per kW hour... its less expensive to heat with electricity.

http://www.maxmcarter.com/fuels/fuelscalc.html

Electric vs Fuels - Comparison Result

Electric:

Electric rate (per kilowatt-hour) = 0.130
Cost of heat (per 100,000 BTU) = 3.81


Fuel:

Propane cost per gallon = 2.79
Burner efficiency factor = 75%
Cost of heat (per 100,000 BTU) = 4.03

[seaeagle2]

if you guys can wait til Friday, I'll use my combustion analyzer and give you an exact answer for my specific furnace.

[S_Davis]

ktmrfs wrote:

S Davis wrote:

ktmrfs wrote:

JaxDad wrote:

beemerphile1 wrote:

sidney wrote:
...Anyone have the real world efficiency rating of the typical RV LP furnace. I'm guessing 70 to 75%....

Why guess? Do the math. Look at the label on YOUR furnace. Divide the output BTU by the input BTU.

That only gives you the combustion efficiency, it does not account for the heat exchangers efficiency.

A typical RV furnace is only ~70% efficient.

I disagree. stated BTU output on a furnace is the BTU output through the heat exchanger. E.G. the BTU of the air coming out of the heat exchanger. BTU input is the BTU of propane or NG going into the burner.

combustion efficiency on a gas furnace is very close to 100%, like most any external combustion vapor fueled appliance.

Well not exactly, when figuring combustion efficiency you have to factor in everything that supports combustion in that appliance. Including heat of exhaust gas. If anyone is close to Mount Vernon WA I have a combustion analyzer I can test your furnace with and give you exact numbers.

If one looks at the BTU of the input gas source and then measures the TOTAL BTU output after combustion, it will be very near 100% for a properly adjust external combustion source. That calculation will include the BTU in the heated exhaust gas and the heat of vaporization of the water as a byproduct of combustion as well as the heat going into the heat exchanger. Basic thermodynamics.

Now, when one looks at the heating efficiency, the input BTU of the fuel and the BTU of the heating output, that's another story, usually well under 100%. 95% for a condensing furnace.

But we are talking about the combustion efficiency of a furnace not a open flame, so you need to account for the loss out the flue and any other losses not going into the conditioned space to figure efficiency.

[ktmrfs]

S Davis wrote:

ktmrfs wrote:

JaxDad wrote:

beemerphile1 wrote:

sidney wrote:
...Anyone have the real world efficiency rating of the typical RV LP furnace. I'm guessing 70 to 75%....

Why guess? Do the math. Look at the label on YOUR furnace. Divide the output BTU by the input BTU.

That only gives you the combustion efficiency, it does not account for the heat exchangers efficiency.

A typical RV furnace is only ~70% efficient.

I disagree. stated BTU output on a furnace is the BTU output through the heat exchanger. E.G. the BTU of the air coming out of the heat exchanger. BTU input is the BTU of propane or NG going into the burner.

combustion efficiency on a gas furnace is very close to 100%, like most any external combustion vapor fueled appliance.

Well not exactly, when figuring combustion efficiency you have to factor in everything that supports combustion in that appliance. Including heat of exhaust gas. If anyone is close to Mount Vernon WA I have a combustion analyzer I can test your furnace with and give you exact numbers.

If one looks at the BTU of the input gas source and then measures the TOTAL BTU output after combustion, it will be very near 100% for a properly adjust external combustion source. That calculation will include the BTU in the heated exhaust gas and the heat of vaporization of the water as a byproduct of combustion as well as the heat going into the heat exchanger. Basic thermodynamics.

Now, when one looks at the heating efficiency, the input BTU of the fuel and the BTU of the heating output, that's another story, usually well under 100%. 95% for a condensing furnace.

[Gdetrailer]

spoon059 wrote:

Gdetrailer wrote:
I know from personal experience that electric resistive heating is much more expensive than propane or natural gas...

Years ago, my DWs uncle had a mobile home that was heated exclusively with an electric resistive furnace. His AVERAGE electric bill was over $500 per month and that was on a "payment plan" deal..

DWs parents had a mobile home 50ft away and used heating oil, their electric bill was $100 per month and the heating oil cost $125 per month on the yearly payment plan...

Have a Cousin with heat pump system for their home, they average 5-8 yrs on a heat pump then it fails...

A lot of "Absolutes" in your statement...
Heating costs depends upon efficiency and fuel costs. An ultra efficient electric heater can be a lot cheaper than an inefficient gas heater. Gas, depending upon availability, can be more expensive than electricity. Natural gas, piped to your house, is usually cheaper than propane, which is trucked to a dealer and then either delivered or picked up by the end user.

The uncle likely paid a little more per month for 3 months out of the year, whereas the parents paid $125/month for the entire year. Based upon the numbers you quoted, it is impossible to determine that the electric heat was more expensive because the electricity is used to power more than the heater. Even still, we don't know the efficiency of the heaters involved, nor the level of insulation of the mobile homes in the scenario.

For direct comparison, when we bought our house we had an oil boiler for heat. First winter we spent $3000 in oil to keep warm over the 4 months December through March. The following spring we had a heat pump installed in our house that replaced an old and inefficient air conditioner. Same house, same insulation, same everything. Electric bills raised by about $120 a month in those same 4 months the next year. Total heating cost was estimated to be $480. A little over 2 years worth of winters would have been our breakeven point... but since the AC was old and the heat pump was much more efficient at cooling, we figure we broke even long before the 2nd year.

Lastly, the "average" life expectancy of a heat pump is closer to 15 years, not 5-8 years.

Not my words, it is THE GOVERNMENTS WORDS below..

HERE

"Electric resistance heating is 100% energy efficient in the sense that all the incoming electric energy is converted to heat. However, most electricity is produced from coal, gas, or oil generators that convert only about 30% of the fuel's energy into electricity. Because of electricity generation and transmission losses, electric heat is often more expensive than heat produced in homes or businesses that use combustion appliances, such as natural gas, propane, and oil furnaces.

If electricity is the only choice, heat pumps are preferable in most climates, as they easily cut electricity use by 50% when compared with electric resistance heating. The exception is in dry climates with either hot or mixed (hot and cold) temperatures (these climates are found in the non-coastal, non-mountainous part of California; the southern tip of Nevada; the southwest corner of Utah; southern and western Arizona; southern and eastern New Mexico; the southeast corner of Colorado; and western Texas). For these dry climates, there are so few heating days that the high cost of heating is not economically significant."

My Cousins live in a climate that deals with LONG PERIODS of high temps (100F-110F) and high humidity for WEEKS to even a month or two during summer and winter down to the upper 30F..

That really means their heatpump must work 24/7/365 unlike milder more temperate areas.

They are now on their 4th Heatpump since they built their house back in the 1970s..

Contrast that to my parents home where they are only on their second gas furnace since they built theirs in the 1950s..

I will take NG any day..

[Harvey51]

Gas heaters are inefficient because much of the heat is lost through the exhaust. This includes radiant heat gas heaters - if it burns gas it has to have an exhaust or it soon makes the air poisonous. Construction site heaters can keep the air reasonably safe by bringing a lot of fresh cold air in, heating it, and then exhausting it.

[S_Davis]

ktmrfs wrote:

JaxDad wrote:

beemerphile1 wrote:

sidney wrote:
...Anyone have the real world efficiency rating of the typical RV LP furnace. I'm guessing 70 to 75%....

Why guess? Do the math. Look at the label on YOUR furnace. Divide the output BTU by the input BTU.

That only gives you the combustion efficiency, it does not account for the heat exchangers efficiency.

A typical RV furnace is only ~70% efficient.

I disagree. stated BTU output on a furnace is the BTU output through the heat exchanger. E.G. the BTU of the air coming out of the heat exchanger. BTU input is the BTU of propane or NG going into the burner.

combustion efficiency on a gas furnace is very close to 100%, like most any external combustion vapor fueled appliance.

Well not exactly, when figuring combustion efficiency you have to factor in everything that supports combustion in that appliance. Including heat of exhaust gas. If anyone is close to Mount Vernon WA I have a combustion analyzer I can test your furnace with and give you exact numbers.

[ktmrfs]

JaxDad wrote:

beemerphile1 wrote:

sidney wrote:
...Anyone have the real world efficiency rating of the typical RV LP furnace. I'm guessing 70 to 75%....

Why guess? Do the math. Look at the label on YOUR furnace. Divide the output BTU by the input BTU.

That only gives you the combustion efficiency, it does not account for the heat exchangers efficiency.

A typical RV furnace is only ~70% efficient.

I disagree. stated BTU output on a furnace is the BTU output through the heat exchanger. E.G. the BTU of the air coming out of the heat exchanger. BTU input is the BTU of propane or NG going into the burner.

combustion efficiency on a gas furnace is very close to 100%, like most any external combustion vapor fueled appliance.

[SidecarFlip]

If someone could post a link for a condensing furnace for RV use, I'd like to see it

[seaeagle2]

One more problem with high efficiency condensing furnaces is the condensate has to drain or the furnace rusts out from the inside, you'd need to have the factory level the furnace, then you'd have to correctly level rv so it would drain....

[JaxDad]

beemerphile1 wrote:

sidney wrote:
...Anyone have the real world efficiency rating of the typical RV LP furnace. I'm guessing 70 to 75%....

Why guess? Do the math. Look at the label on YOUR furnace. Divide the output BTU by the input BTU.

That only gives you the combustion efficiency, it does not account for the heat exchangers efficiency.

A typical RV furnace is only ~70% efficient.

[spoon059]

Gdetrailer wrote:
I know from personal experience that electric resistive heating is much more expensive than propane or natural gas...

Years ago, my DWs uncle had a mobile home that was heated exclusively with an electric resistive furnace. His AVERAGE electric bill was over $500 per month and that was on a "payment plan" deal..

DWs parents had a mobile home 50ft away and used heating oil, their electric bill was $100 per month and the heating oil cost $125 per month on the yearly payment plan...

Have a Cousin with heat pump system for their home, they average 5-8 yrs on a heat pump then it fails...

A lot of "Absolutes" in your statement...
Heating costs depends upon efficiency and fuel costs. An ultra efficient electric heater can be a lot cheaper than an inefficient gas heater. Gas, depending upon availability, can be more expensive than electricity. Natural gas, piped to your house, is usually cheaper than propane, which is trucked to a dealer and then either delivered or picked up by the end user.

The uncle likely paid a little more per month for 3 months out of the year, whereas the parents paid $125/month for the entire year. Based upon the numbers you quoted, it is impossible to determine that the electric heat was more expensive because the electricity is used to power more than the heater. Even still, we don't know the efficiency of the heaters involved, nor the level of insulation of the mobile homes in the scenario.

For direct comparison, when we bought our house we had an oil boiler for heat. First winter we spent $3000 in oil to keep warm over the 4 months December through March. The following spring we had a heat pump installed in our house that replaced an old and inefficient air conditioner. Same house, same insulation, same everything. Electric bills raised by about $120 a month in those same 4 months the next year. Total heating cost was estimated to be $480. A little over 2 years worth of winters would have been our breakeven point... but since the AC was old and the heat pump was much more efficient at cooling, we figure we broke even long before the 2nd year.

Lastly, the "average" life expectancy of a heat pump is closer to 15 years, not 5-8 years.

[beemerphile1]

sidney wrote:
...Anyone have the real world efficiency rating of the typical RV LP furnace. I'm guessing 70 to 75%....

Why guess? Do the math. Look at the label on YOUR furnace. Divide the output BTU by the input BTU.

[Gdetrailer]

RGar974417 wrote:
If you're in a campground with electric hookup,electric heat is cheaper because the campground is paying for it LOL. Which one will be cheaper depends on the cost of propane and the cost of electricity.Here's a good article to figure it out: http://homeguides.sfgate.com/cheaper-use-propane-gas-electricity-home-101763.html

If I read it correctly, the OP has a METERED SITE.

There is no way that paying for electric heat on a metered site is going to any cheaper.

I know from personal experience that electric resistive heating is much more expensive than propane or natural gas.

Years ago, my DWs uncle had a mobile home that was heated exclusively with an electric resistive furnace. His AVERAGE electric bill was over $500 per month and that was on a "payment plan" deal..

DWs parents had a mobile home 50ft away and used heating oil, their electric bill was $100 per month and the heating oil cost $125 per month on the yearly payment plan.

A Church I used to go to had an electric resistive hydronic heating system, cost $4,000 per month for electric on a yearly payment plan..

Eventually they replaced the electric boiler with a gas fired boiler..

Result was $1,000 electric bills and $1,000 gas bills..

Like mentioned before, the ONLY way electric heating can be made "affordable" is to go with a HEAT PUMP. The big downside to a heatpump is the EXPENSE, they are insanely priced.

The other downside to heat pumps are that they can be unreliable due to the reversing valves that can fail.. Often results in REPLACING the heat pump due to either parts not available or the cost to repair is nearly the cost of new..

Have a Cousin with heat pump system for their home, they average 5-8 yrs on a heat pump then it fails.. The last time it failed, it cost them nearly $6,000 for a new one since the valve that failed was no longer available..

OPs best bet is to either find a campground which does not meter the electricity or look into 100 lb propane tanks which will be much lower cost to refill due to propane being cheaper in bulk quantities..

The OP didn't say what temp they are trying to stay at but, they can lower the temp then use sweaters, add a extra layer by wearing two pairs of socks and so on..

If they are trying to keep a RV at say 70 F when outdoor temp is say 30 F they can save huge amounts of cost by lowering the temp to say 60F..

It isn't insulated like a sticks and bricks so you cannot expect it to be low cost to heat..

Night time they can add electric blanket or heated bed pad and lower the thermostat a bit more..

I don't like cold, so I don't bother with cold weather camping, just way to much work and expense for me.. I would rather stay home and toss a few extra logs in my wood furnace and watch the cars sliding on the ice and snow from my home windows..

[rhagfo]

Gdetrailer wrote:

sidney wrote:

Gdetrailer wrote:
As Sidecar mentions, they are not built for efficiency, but neither is most RVs.

Your in Alaska, I hope you are not planning to live in a RV for the winter..

You have at the most R3 in the floor and the walls R6 and roof R11 in the center, single pane windows with nice cold aluminum frames..

You have not much more than a oversized wooden fishing hut on wheels.

You are going to use twice as much energy whether it is propane or electric than what you think you might.

Yeah, you ARE going to be cold and broke..

I would be looking at super insulating before trying to calculate the cheapest heat.

Nope not in Alaska... we are in Utah right now. ( Our 5th wheel has never been in AK... we store it in the lower 48.)

I'm cheap and just trying to save a buck.

Still gets COLD in Utah, still have the same insulation problem, still have the same windows, still have the same furnace..

Still not cheap to heat or stay warm in a poorly insulated box on wheels.

Electric RESISTANCE heat if you are paying for it WILL be MUCH MORE EXPENSIVE than propane even counting in the lack of efficiency of the RV furnace.

The only way electric heating cost can be lowered is if you have an electric heat pump. Heat pumps are an air conditioner that reverses, it extracts heat from the colder outside air when heating.

Downside is it costs more to buy, is more complicated and costly to repair and tends to drop efficiency as the outside air gets colder and there is a point when it is too cold for outside air and relies on resistance heat..

Additionally, if you are stuck with 30A shore power you WILL be limited to 1,500 watts or about 5500 BTU of electric heat which in a big RV is nothing, and that is long as you turn off the electric heat to the water heater if equipped.

You would need a 50A shore power setup to be able to supply more than 1500W of electric heat..

RVrs using electric heat tend to be the ones that DO NOT HAVE METERED ELECTRIC. In other words they pay a flat fee for the lot which includes electric at no additional cost.

Pony up or find a different campground that doesn't meter the electric as a separate fee..

Actually with the Cheap Heat system does 1,800 watts on a 20 amp circuit. I ran our system on a 30 amp system and never popped a breaker. Keep us nice and warm into the low 40’s overnight.