Ideas for a more electrically efficient heater?

Since the OP has received two pages of suggestions and seems to have made up his/her mind, I am going to close this thread.
No need for further discussion now.
Barney

> Since you don't want to use a generator, you are pretty much stuck, my suggestion is more battery or add more solar..

Um... I could also just get a catalytic or a Buddy heater.

> To me, a generator is more "economical" and "practical".. Even a SMALL 1000W gen would go a long, long way to making your situation work very well.

Good lord no, I hate generators. The first thing I do when I get a new RV is tear the **** thing out to make room for more batteries. Generators are just too obnoxious to my neighbhors. I do my camping at the beach, and I absolutely hate when someone parked next to me has their generator aimed at me just so they can watch their TV all day. Or worse yet, use it to make electrically brewed coffee! Or use their microwave. I've found with just a little bit of ingenuity a generator is absolutely unnecessary for an RV.

wrybread wrote:
> I have yet to see an RV furnace use anything other than the STD Cheepie squirrel cage

I guess the big question is, is there a viable alternative to a "cheapie squirrel cage"?

> The one with the smaller motor, 5.5 amp drain will move less CuFt of warm air through the RV

Which in most cases is just fine. Remember, catalytic heaters have no fan at all and they heat a camper very well.

The answer is NO.

There is no "viable" alternative to the squirrel cage fan that the furnace manufacturer used.

The squirrel cage fan design is more efficient and effective than using a three, four or five fan blade design.. Not to mention actually quieter per CFM of air movement.

You also need to realize that removing or altering the cage fan will affect the speed and RPM of the motor it is attached to..

This motor is double shafted, it has one shaft for the inside squirrel cage (your inside air) and the other shaft is the combustion chamber draft inducer.

If draft inducer is too slow, the sail switch (a safety item) will fail to enable the burner..

If draft inducer is too fast you will push the heat from the flame out the exhaust too fast burning up more propane and causing your furnace to put out very little heat for each BTU burned.

You would have to totally re-engineer your furnace from the fan to the burner (in other words you can not slow down the fan CFM without having to reduce the fuel being burned).

DO NOT BLOCK ANY VENTS!!! PERIOD!

Each BTU range of a furnace has a very specific MINIMUM amount of venting area which IS REQUIRED for correct safe operating parameters.

The RV manufacturer will have put in the correct minimum amount of vents for the BTU range of the furnace.

You CAN add more vents but you should never, ever block or remove vents for safe operation. Doing so can cause the furnace to overheat and possibly cause a RV FIRE.

My suggestion is if you are so concerned about the furnace using up your battery, then buy a lower BTU furnace that has a lower fan CFM. The downside of this is if you choose too small of a furnace it will NEVER turn off.. This will result in MORE battery usage than what you have now.

Since you don't want to use a generator, you are pretty much stuck, my suggestion is more battery or add more solar..

To me, a generator is more "economical" and "practical".. Even a SMALL 1000W gen would go a long, long way to making your situation work very well.

Yes they do
we have a Wave 8

i covered both those >points in a previous post

> I have yet to see an RV furnace use anything other than the STD Cheepie squirrel cage

I guess the big question is, is there a viable alternative to a "cheapie squirrel cage"?

> The one with the smaller motor, 5.5 amp drain will move less CuFt of warm air through the RV

Which in most cases is just fine. Remember, catalytic heaters have no fan at all and they heat a camper very well.

Drew
I won't argue fan design with you
I ask you to stop and think about this for a moment
I have yet to see an RV furnace use anything other than the STD Cheepie squirrel cage, in the RV heater box for the moving the heated air through the ducts
Given that all use the same basic design
And the ducts are not restricted
What i said holds true
We are not talking about theoretical design efficiency here
You want to use less battery energy with the RV furnace you WILL move less air

If you test the heaters you mentioned
The one with the smaller motor, 5.5 amp drain will move less CuFt of warm air through the RV

I replaced the standard RV furnace with a "Sportsman" heater, basically a gas ring in a tin can. It is vented, has a regulated gas safety valve, and is rated at 20K BTU. Of course, it's no longer sold. There are similar fish house heaters that use no electricity.

I have thoughts of a hydronic system powered by the water heater and a small circulating pump.

If you are thinking a more 12v efficient furnace here is a spec sheet:
Suburban_Service_Manual.pdf pg 21 & 22
Check BTU per 12v amp

Have also seen some two speed furnaces that might be easier on the battery.

I've got 4 Trojan t105's (and ha, plenty of blankets) and can run the furnace for awhile but I'd rather not use something so brutally inefficient when boondocking, especially when there's no sun for a day or two. And I should probably mention that I don't have a generator, just pure solar. With that setup if you're somewhere cold with not much sun for a couple of days you're pretty much guaranteed to run out of power if you're using a blower, no matter what batteries you have.

But no biggie since catalytic heaters seem to work great.

But sure would be nice to figure out some way to use a smaller blower, maybe routed to just one or two vents. Of course would need to make sure the heater can't overheat.

MrWizard wrote:
it takes a xxx amount of energy to move yyy amount of air
you can get a furnace with lower btu and smaller fan motor

or you can eliminate all fan power use by getting the Wave cat heater

thats what we did, use to have a wave 6, now have a wave 8

we are 34ft DP, the bed sets over the engine compartment and gets COLD

It's not really true that a fixed amount of air movement requires a specific amount of energy; there can be significant differences in fan efficiency. A large fan will move a given quantity of air with less energy than a small fan, as the air velocity is lower and hence the pressure differential created is lower. This incidentally is why a helicopter is able to fly without needing impossibly large engines. Also, some fan designs waste less energy in making noise or eddy currents or turbulence than other fan designs.

For a furnace, there's also the option of heating a little air to a higher temperature vs. heating a lot of air to a lower temperature. The heat output can be the same, but the volume of air moved is different (and the evenness of the heat presumably suffers with the lower volume fan).

Looking online, an Atwood Excalibur 30,000 BTU ducted furnace is rated at 7.5A, while a Suburban NT30 (also 30,000 BTU and ducted) is rated at 5.5A.