Things to look for when buying a furnace?

[Oregonconversion]

Atwood? Surburban?

What features should I get if I want to be lazy?

Is there a such furnace that will work on LP or electric like the water heaters?

What about AC? Any of them have AC?

[luvrbus]

never saw one that would work both ways but both are available with 12v or 120v blower motors     good luck

[Oregonconversion]

Is there any way to heat with electric that is efficient? I will be on shore power most of the time.

[JackConrad]

Is there any way to heat with electric that is efficient? I will be on shore power most of the time.

That will depend in part on how well your bus is sealed and insulated as well as outside air temps you will be staying in.  Jack

[Oregonconversion]

Is there a central air that will work off 110V?

[Sean]

Is there any way to heat with electric that is efficient? I will be on shore power most of the time.

I'm guessing that's not really the question you want to ask.

Almost all electric heaters are 100% efficient.  Which is to say, that all the electric power consumed by the device is turned directly into heat.

I'm guessing that, rather than "efficient" you meant "effective."  This is a different story.  Adding a circulating fan to a heater will not make it more efficient, but will, for most purposes, make it more effective, in that the heat will be spread out over a larger area.

The real problem here is that you have only a limited amount of electric power coming into the coach, whereas LPG or diesel heaters can use an essentially unlimited quantity of fuel to produce whatever output is desired, right up until the tank runs out.  And, BTW, if you use LPG (propane) for space heating, you will go through a lot of it -- propane has far less energy content than, say, diesel.

Furnaces (and air conditioners, for that matter) are rated in British Thermal Units per Hour, or BTU/h (not just BTU, as is often mis-written).  A typical RV LP furnace might be rated anywhere from 22,000 to 35,000 BTU/h.  To produce 35,000 BTU/h, an LP furnace will burn about half a gallon of liquid LPG (there are 90,000 BTU in a gallon of LPG, but the furnace is not 100% efficient -- a lot of the heat goes up the flue with the hot gasses), so a "barbeque" tank would run such a furnace (full-time) for a mere eight hours.

By contrast, a typical portable electric heater that you could buy at, say, Wal-Mart would be rated at 1,500 Watts.  One watt is about 3.414 BTU/h, so these heaters can produce at most 5,118 BTU/h.  You'd need seven of them running full tilt to get as much heat as that 35,000 BTU/h gas furnace.  Those seven units would consume 10,500 watts.  To put that in perspective, a 30-amp park service produces a maximum of 3,600 watts, and a 50-amp park service produces a maximum of 12,000 watts.  (This is the reason that there are no LP/Electric combination furnaces.)

So, yes, you could get as much heat as a gas furnace if you have half a dozen or so electric heaters and a 50-amp park connection.  And there are, indeed, systems to heat an RV electrically that are less unwieldy than half a dozen portable heaters; for example, an AquaHot system has one or two 1,650-watt electric elements (5,630 BTU/h each) to heat the hydronic fluid.

In most cases, though, you can get by with much less heat.  That LP furnace will not be burning full-time, but, rather, will cycle on and off, with the "on" cycle being perhaps as little as 20% of the time.  That means that you are effectively delivering as little as 700-1000 BTU/h of heat, well within the capability of small electric heaters.

In our coach, in addition to our 45,000 BTU/h diesel-fired hydronic system, we have a pair of built-in electric "toe-kick" heaters of about 1,000 watts (3,400 BTU/h) each, as well as one of those Wal-Mart specials for another 1,500 watts (5,100 BTU/h) for when we happen to be plugged in.  Those tend to keep us plenty warm down to the 40's or so, but tend to run full-time to do so.  Then again, we have really good insulation in our coach.

Hope this helps.

-Sean
http://OurOdyssey.BlogSpot.com

[NJT 5573]

Two little ones, one in each end is more effecient than one big one. Less pull on the 12 volt system as well as less fuel. Its harder to heat the water bay with 2, but its better for comfort and costs, lots of times, one is enough.

I prefer my Little Buddy for all my heating, nothing could be more effecient and it runs almost 5 days on 4 gal of propane on low heat, but my bus is pretty tight.

My 40,000 BTU Surbaban is real hard on the batterys and the propane, but it does the job I bought it for, and also heats the water bay.

[Oregonconversion]

I have a big buddy hooked up to a 40# tank. Will this be as cost effective as 2 small furnaces?

Also, how does these tow-kick heaters work? Where do they get the hot water from?

[Sean]

Also, how does these tow-kick heaters work? Where do they get the hot water from?

Electric toe-kick heaters do not involve any water.

Hydronic toe-kick heaters can be plumbed in many ways.  Usually, a diesel-fired boiler is involved, such as a Webasto, Pro-Heat, or Eberspacher (Espar), or a thermal-mass type system such as the AquaHot, which itself uses a Webasto boiler.

The boiler heats the hydronic fluid (which is usually a 50/50 antifreeze mix, not plain water), and a circulating pump pumps it through the coach, including through the fan-coil units (hydronic toe-kick heaters) and a heat exchanger coil in the water heater.  A two-way valve lets you bypass the fan-coil space heaters, to just get domestic hot water.

An additional heat exchanger between the house hydronic system and the engine coolant loop will allow you to use waste heat from the engine to heat the coach and provide domestic hot water while you are driving.  We often find that we do not need to use the boiler at all if we drive daily.  Adding a small electric pump to the engine loop allows you to pre-heat the engine from the diesel boiler for easier starts on cold days.

Some folks choose to combine the house hydronic loop and the engine loop into one system, but I recommend against this.

The AquaHot system also allows you to heat the hydronic fluid with one or two electric elements.  It also provides "endless" hot water by circulating domestic water through a heat exchanger in the thermal tank (as opposed to the other way around for conventional hydronic systems).

-Sean
http://OurOdyssey.BlogSpot.com

[Oregonconversion]

Thanks for the clarification Sean.

One last question if you can break it down for me.


What is the cheapest way to heat my bus when hooked up to shore power 100% of the time?

[Lee Bradley]

Have you consistered a heat pump? It doesn't convert energy into heat but rather uses energy to move heat from one place to another; from inside the cold box to outside, from inside the bus to outside or from outside the bus to inside.

[TomC]

As Lee said, above 40 degrees, a heat pump (reverse cycle air conditioner) will produce almost as many BTU/hr (like Sean says) heat as it does cold.  If you have a very well insulated bus (I have 2.25" blown in insulation), then two of the portable electric heaters will do a good job mostly keeping the bus warm, with some running of the furnace.  I have an Atwood 35,000BTU/hr propane furnace that has been 100% trouble free since installing 10 years ago (just clean it once a year).  Both Atwood and Suburban make two speed furnaces for quieter running.  Also, Atwood requires a 16" x 6" (approximate size) door on the side for access to the furnace (it is installed from the outside).  Suburban has the same, but also a ducted unit that has just a small intake and exhaust plate on the side of the bus-which I'll use next-not so prominate.  I have only my stove and furnace being propane, with both next to each other with the propane tank (20gal chassis mount) directly below for short gas line run.  Also have an electric solenoid valve shutoff controlled from inside so the gas is off when not in use.  Good Luck, TomC

[JohnEd]

Your "Buddy" adds a lot of water to the air.  It is also the most efficient gas heater.  They are great and economical but I won't have one.

Everybody has the little 1,500 watt electric cube heaters for when hooked to the pole.   They work well in the extreme and all you need to do is keep the little filter clean.  That might be a chore with a lot of foot traffic raising dust at the floor where the cubes will always live and work best.

Propane furnace is the way to go.  Used ones are around and they are repairable...usually.  Chec before you buy.  The Suburban that goes in thru the wall is noisy as far as I can tell.  The unit that mounts under a sink or in the back of a cupboard is the "hot" set up for me.  Pun intended.  These things spew heat in less than a minute are are somewhat efficient.  My uses far less propane that whatever Sean is familiar with.  First time I have ever come close to disagreeing with him.  I know it is a much added expense but get a gas furnace for the rear and one for the front.  Redundancy is smart.  45,000 BTU front and 30,000 BTU for the rear.

You can get a heat pump that is the same size as a roof air.  Works great, I'm told.  15,000 BTU in AC mode but less in the heat mode I think.  I think you need 3.  Check the yellow pages...net,,, on prices.

Make sure you have lots of outlets near the floor and all of them are on different breakers.

HTH,

John

[Sean]

What is the cheapest way to heat my bus when hooked up to shore power 100% of the time?

That depends on whether or not you are paying for the electricity, and, if so, at what rate.

Utility power in the US runs anywhere from $.09 to over $.21 per kWh.  If you own the power pole (say, for example, you own a piece of property and put in a residential service), that's what you will pay.  However, at campgrounds, the rate is usually far higher.

Now, mind you, most campgrounds do not charge "transient" guests extra for electric power (although many of them forbid the use of electric heaters).  However, guests staying on weekly or monthly rates, or longer, generally have metered electric service and they are charged on consumption.

Right now, a gallon of diesel goes for around $2.05.  There are 130,000 BTU in a gallon of diesel, and, figuring, say, 90% efficiency for a hydronic system, that's less than .002 cents per BTU.  Since there are 3,414 BTU in a kWh, that equates to about 6 cents per kWh.  So at today's diesel price, you'd have to be able to get your electricity for less than $0.06 per kWh for resistive electric heat to be cheaper than diesel.  At $4 per gallon, electric heat becomes competetive at $0.12 per kWh, which is closer to market rates.

As Lee and Tom suggest, you can improve on this with a heat pump, which "moves" heat from outside to inside.  A typical RV heat pump in heating mode will provide about 6 BTU/h of heating per watt of electricity at 47°.  That's just under twice as much heat per watt as resistive heating, and so you can double the limits mentioned above.  But bear in mind, they don't work at all below 40°, and so you will need to have a resistive heat system as well, or else plan to use a diesel or LP furnace in those conditions.

On a 50-amp service, you could run four of these "13.5" heat pumps (which produce 11,600 BTU/h at 1,845 watts at 47°), and that would give you a respectable 46kBTU/h -- as much as a Webasto diesel boiler.  Again, it all depends on what you pay for the electricity.  If it is included in your camp site rate, and you are allowed all you can use, this is probably the way to go.  If you are paying more than $.12 per kWh (which would be very cheap, indeed, at an RV park), then diesel is almost certainly cheaper.  And, if you put in a quality diesel (or LP) system, you'll still have plenty of heat when you don't have shore power.

We tend to look at commercial RV park rates as "power" rates, since that's usually the only reason we'll stay there.  Even if we are in freezing weather, we couldn't use more than 8 gallons of diesel (~$17) in a 24-hour period, and, more realistically, it's half that (the boiler doesn't run full-time, and we turn the heat down at night and when we are away).  If you add in our average of one hour per day of generator run time (another gallon), we're looking at 5 gallons a day, or roughly $11.  Unless we can get a camp site for less than that, it's cheaper to boondock.  When diesel was $4.50 per gallon, of course, $23 camp sites started to look pretty good.

Hope that helps.

...  My uses far less propane that whatever Sean is familiar with.  First time I have ever come close to disagreeing with him.

John, furnace efficiencies are all over the map.  Some are better than 90%, some are lower than 80%.  But even if it was 100% efficient, you'd still need 0.38 of a gallon of LP every hour to run a 35,000 BTU/hr furnace -- there's only 90,000 (or fewer) BTU in a gallon of LPG.  A BBQ tank holds four liquid gallons of LP, so absolutely the best you could get would be 10.5 hours of run time on a tank that size.  I think I wrote 8, which would be a hair under 80% efficient, and yours might be closer to 90% or even higher.

Few people, of course, would try to run a furnace on a BBQ tank (well, maybe in a pop-up trailer or other rig that only had that size tank).  I'm guessing that if you actually measure your usage in gallons/hour while the unit is actually running (keeping in mind that seldom, if ever, will an LP furnace run continuously), you will find the usage to be somewhere between 0.4 and 0.5 gph (if it's a 35,000 BTU/h unit -- less if it's smaller, of course).  FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

...  A BBQ tank holds four liquid gallons of LP, so absolutely the best you could get would be 10.5 hours of run time on a tank that size.  I think I wrote 8, which would be a hair under 80% efficient, and yours might be closer to 90% or even higher.

OK, I admit it, I goofed.  Too many numbers swimming in my head.  I just checked, and a BBQ tank holds 4.7 gallons of liquid LPG, not 4.0 as I presumed in my example.

So an 80% efficient 35,000 BTU/h furnace could run 9.7 hours, and a 90% efficient model could run 10.9 hours on such a tank.  Should anyone ever need to do so.

The rest of my math was correct, I just forgot how big a BBQ tank is.

-Sean
http://OurOdyssey.BlogSpot.com