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FURNACE FAN POWER REQUIREMENT

Braces
Explorer
Explorer
2014 Montana High Country Thinking of changing to two 6volt batteries. Don't have access to my trailer right now and need to know how much power the fan uses to see if running furnace at night when cannot run the generator would be practical. No genny 8 to 8 in national park. I realize there are a lot of variables so if you know the approx power draw of the fan motor maybe I could have a reasonable idea of the amp/hrs needed to keep reasonably warm.
14 REPLIES 14

2oldman
Explorer II
Explorer II
pnichols wrote:
SidecarFlip wrote:
Keep in m mind that the furnace blower only runs intermittently. Not continuously.
Excellent point that seems to be "lost" on many that complain about their propane furnace sucking up so much battery current. I suspect that they may have a weak, or too small, RV battery bank problem instead.
Or it's really cold and they want the coach at 70F.
"If I'm wearing long pants, I'm too far north" - 2oldman

pnichols
Explorer II
Explorer II
SidecarFlip wrote:
Keep in m mind that the furnace blower only runs intermittently. Not continuously.


Excellent point that seems to be "lost" on many that complain about their propane furnace sucking up so much battery current. I suspect that they may have a weak, or too small, RV battery bank problem instead.

Our furnace runs maybe for 8-10 minutes every 15 minutes, or so, during nights with outside temps in the 30's. That means ~7 amps (furnace draw) for 8-10 minutes every 15 minutes, or so. This translates into around 32 amp hours, total, per 8 hour furnace run per night. Running the furnace all night plus a lot of the day too - is a whole different situation.

32 amp hours should not deplete "a good battery per night". However, we have our furnace control set at only around 62-64 degrees during the night.
2005 E450 Itasca 24V Class C

MEXICOWANDERER
Explorer
Explorer
Major influences

Size of rig

Insulation of rig

Condition of heater. Is kitchen at 75F bedroom in the high 40's?

Consider modifications. The canned peas and throw pillows really do not need to be kept warm and comfortable at two AM.

Where? North slope of Alaska? Quartzite?

Temp maintenance demand of owners. Some tolerate 50's, others 70's

One way to decrease side-effects is to put your generator at attention when you start it and not at parade rest. Means converter and charger upgrades. 6 cells of GC220 will suck 100+ amps when starting off. Six cells of 27 or 31, close to forty amperes.

Boon_Docker
Explorer III
Explorer III
SoundGuy wrote:
old guy wrote:
you will benefit with more power with the 6's then with one or even with using two 12's. the 6's will last longer


A generalized statement that simply isn't true - a pair of G31 12 volt deep cycle batteries wired in parallel offer approximately the same AH capacity as a pair of GC-2 6 volt deep cycle batteries wired in series. For those running heavy loads with an inverter a pair of 12 volts can actually be preferable as they're more likely to suffer less voltage drop under heavy inverter load than will a pair of 6 volts. The devil is in the details. ๐Ÿ˜‰


May be the same AH, but the G31 is also a larger battery than a GC-2.

ScottG
Nomad
Nomad
The 30K Suburban in our last TT drew 6 amps.

BFL13
Explorer II
Explorer II
Braces wrote:
2014 Montana High Country Thinking of changing to two 6volt batteries. Don't have access to my trailer right now and need to know how much power the fan uses to see if running furnace at night when cannot run the generator would be practical. No genny 8 to 8 in national park. I realize there are a lot of variables so if you know the approx power draw of the fan motor maybe I could have a reasonable idea of the amp/hrs needed to keep reasonably warm.


Depends on outside temp and how big a barn you are trying to heat at what temp inside, of course, but for example with our 5er, we use about 70 AH a day with no furnace, which already means we need 140 AH of battery bank just for that--say two 24 size 12s at minimum.

So add some furnace. Fall, Spring, we use about another 70 AH but in Winter (around freezing outside overnight, but not colder than that) that can go to 100 or so AH for the furnace. The 70AH goes up too with it being dark out longer so more lights on longer time.

So now it is 140AH in one day but can go as high as 200. BTDT. How much battery bank? Double those AHs (50% used then recharge) so 280AH to 400AH needed and a recharge every day. A pair of 6s will do 225, so not enough for us, but others might survive by reading by candle light while wrapped in blankets in their 5er because they don't have enough of a battery bank.

But that's not the whole story! You can only recharge to about 90% with your generator, so the recharge is a "50-90" or 40% of the bank not 50%, so you need to survive on that 40% between recharges. So taking that 140AH as your daily 40% that means 100% is 350AH needed for the battery bank. Two 6s can't come close--needs four.

Another thing is in parks with gen hours, how long will the gen have to run to replace 140AH as a 50-90? That depends on how big an amp charger you have and how big a gen you have to run that big amp charger--which needs to get the batts to 14.4 or higher 14.8 is best. (except we are talking cold out, so add some voltage to those numbers for temp comp.-- 14.8 is 15.2 at 32F. Can your charger do 15.2?)

If you want it all to work out, you should fit the 5er out with four batteries 6s or 12s to something like 450AH of bank. Get a PowerMax 100 amp ADJ(ustable voltage) charger (or equivalent--if you can find an equivalent), and a 3000w inverter gen to run it (a 2000 is too small). Now you are good to go for Fall and Spring.

In winter we carry two more batteries for a six battery bank so we can do that 200AH a day without having to change our ways. No furnace quitting at 3am for lack of 12v power in our case--once as a newbie is enough to learn about that! ๐Ÿ™‚
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

SidecarFlip
Explorer III
Explorer III
Keep in m mind that the furnace blower only runs intermittently. Not continuously.
2015 Backpack SS1500
1997 Ford 7.3 OBS 4x4 CC LB

red31
Explorer
Explorer
old guy wrote:
you will benefit with more power with the 6's then with one or even with using two 12's. the 6's will last longer


twice the cycle life = mo power

http://www.pbase.com/mainecruising/deep_cycle_battery&page=1

Flyfasteddie
Explorer
Explorer
I have a 31,000 BTU non-ducted furnace and the fan pulls 5.8-6.2 amps.

All_I_could_aff
Explorer
Explorer
Mine pulls 3.8 - 4 amps running, but it's a rather small non ducted unit. I believe it says either 8000 or 10,000 BTU on it
1999 R-Vision Trail Light B17 hybrid
2006 Explorer Eddie Bauer
2002 Xterra rollinโ€™ on 33โ€™s
1993 Chevy Z24 Convertible
Lives in garage 71,000 miles

SoundGuy
Explorer
Explorer
old guy wrote:
you will benefit with more power with the 6's then with one or even with using two 12's. the 6's will last longer


A generalized statement that simply isn't true - a pair of G31 12 volt deep cycle batteries wired in parallel offer approximately the same AH capacity as a pair of GC-2 6 volt deep cycle batteries wired in series. For those running heavy loads with an inverter a pair of 12 volts can actually be preferable as they're more likely to suffer less voltage drop under heavy inverter load than will a pair of 6 volts. The devil is in the details. ๐Ÿ˜‰
2012 Silverado 1500 Crew Cab
2014 Coachmen Freedom Express 192RBS
2003 Fleetwood Yuma * 2008 K-Z Spree 240BH-LX
2007 TrailCruiser C21RBH * 2000 Fleetwood Santa Fe
1998 Jayco 10UD * 1969 Coleman CT380

2oldman
Explorer II
Explorer II
About 7 amps.
"If I'm wearing long pants, I'm too far north" - 2oldman

Old-Biscuit
Explorer III
Explorer III
Old adage ---One 12V battery good for One night of furnace

Course your typical RV 12V battery is roughly 120 AH

Two 6V batteries.......12V DC BUT higher amp hour ratings.....closer to 200 AH

(TWO 12V batteries wired in parallel ----same 12V but double amp hour----12V/100AH each equals 12V/200 AH)
(Two 6V batteries wired in series........double voltage but same amp hour----6V at 200 AH each equals 12V/200 AH)


SO TWO 6V can provide MORE AH then ONE 12V

What is AH Rating of current 12V?
What is AH Rating of the 6Vs?
Is it time for your medication or mine?


2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31

old_guy
Explorer
Explorer
I used two 6's when elk hunting and recharged the next day. at first i used two 12's and then switched over to 6's. you will benefit with more power with the 6's then with one or even with using two 12's. the 6's will last longer