How big a furnace for 23' Safari?

[ronstory]

We've gutted the kitchen cabinet and I want to put in one about 50" long vs. the 56"ish original. We want a bit more space up front and this means that I get to buy a brand new furnace in. Darn.

I've been searching and a lot of folks seem happy with the Olympian wave cat heaters. So I'm trying to figure out if I could just get away with a Cat heater or just look for a small furance like:

eBay Motors: Atwood Hydro Flame 8012 12,000 BTU RV Trailer Furnace (item 280270797231 end time Oct-24-08 13:58:08 PDT)

The Hydro-flame 8012 only draws 1.8 amps when running and is 12KBTU.

Do I need more? I know that more is better... but call me cautious.

[53flyingcloud]

Depends on the type of new insulation that you put into the Airstream..If not, I would think the 12KBTU unit is just a tad too small. IMHO..I would spend the extra monies and go for the 34KBTU..You can always use the Olympian heater on less than severe cold days.
Good Luck~!
53FC

[bhayden]

Originally Posted by ronstory

I know that more is better... but call me cautious.

Wrong ! More is not better when it comes to furnaces. An oversized furnace will short cycle which is not only less comfortable it shortens the life of the furnace and uses more fuel. Couple that with likely costing more up front and it's a lose lose proposition.

You need to know the heating load required by your trailer. If you're upgrading the insulation that's a very good thing but the lower heat loss will mean a smaller furnace. You also need to make a decision on what the coldest temperature you'll be camping in off grid (if plugged in to shore power then you can easily supplement with an electric heater.

The Atwood you linked to looks like a nice furnace. No standing pilot is a nice touch (when it works ). The Atwood literature for their own digital thermostat says it uses the air conditioner fan to continuously circulate the air. I'm assuming that means the furnace fan cannot be wired to do this? That's too bad since the air conditioner fan will only operate when you''ve got 120VAC.

The Wave Cat heaters are an interesting product. They don't drain your 12 battery and more importantly, keep you warm even if your battery is dead. I guess the big drawback is no thermostat capability. But I think I'd be willing to get up at night and adjust the heater or vent (or blanket). The damn furnace fan's going to wake you up anyway

[ronstory]

The more is better line was an attempt at humor... apparently feeble in my case.

I just found Balgrn's install of the 8012 in his 74 Overlander.

Furnace Upgrade

... and he thought the furnace was rather quiet a plus.

As for a 34K BTU model... I formerly had 1972 4K sqft house with a ton windows and "only" had a 150K BTU furnace that was 90% efficent. I'm thinking between the 12K hydroflame and the 18K BTU for our humble trailer.

The trailer's insulation is original... and so far every panel I've removed has insulation behind it so I seem to be have been spared the "compacting" insulation issue. Now my sample size is small, but I could always address that later.

[ronstory]

Does anyone know how many BTU's the NT-22 put out? I'm thinking "22" is for KBTU but can't seem to find a definate answer via google.

Also, any idea what the efficienty on these mid 70's furnaces?

[bhayden]

Originally Posted by ronstory

The more is better line was an attempt at humor...

What's not funny is how many HVAC companies oversize furnaces in houses. Partially because they don't want to or don't know how to calculate the heating load and partially because customers tend to think they're "cheaping out" on them if they try to install a furnace smaller than what was originally in the house. So what if it rotted out in 10 years because it was constanly short cycling

Originally Posted by ronstory

I just found Balgrn's install of the 8012 in his 74 Overlander. ... and he thought the furnace was rather quiet a plus.

Quite is a big plus. Now, if there were only some variable speed modulating furnaces available for RV's. Seems like it would be a great application. The question is would enough people pay 2X the cost.

As for a 34K BTU model... I formerly had 1972 4K sqft house with a ton windows and "only" had a 150K BTU furnace

Yep, the house may have been better insulated but it was probably designed for a minimum outside temperature of 0 +/- 10 degrees F.

The trailer's insulation is original... I could always address that later.

Exactly. Time and money spent on insulation help with both heating and cooling. Heating the great outdoors is a losing proposition.

We haven't been camping in the winter but have had the trailer in the north Cascades in October when night time lows were near freezing. Even then a 1500 watt space heater was more than adaquate for out 24' Argosy. 1500 watts is about 5000 BTU output. Most furnaces are rated on input and the best they can do non-condensing is 80% so that's a little over 6000 BTU. Even if you figure only 60% efficient that's only 8,500 BTU at freezing. 12k BTU should be plenty unless you're planning a lot of winter trips up to the tundra

[ronstory]

Bhaden--

Yes, when I had the furnance installed in my old house, I "downgraded" from a 180K BTU (@ probably 75% efficentcy) to a 150K at 90%. Worked just fine and the cycle times were quite reasonable.

After your feedback, I'm going to just get the 12K BTU but I'll have a cat as well just in case. The other nice thing about the Atwood hyrdoflame 8012 is it's rated at only 1.8A 12V when running, where the larger BTU hydroflame 7000 series uses close to double the amperage. Smaller is better in this case.

[bhayden]

Originally Posted by ronstory

Bhaden--
I'm going to just get the 12K BTU but I'll have a cat as well just in case.

I'll bet the Cat is all you use or use 90% of the time. It would be nice if there was a way to run just the fan on the Atwood. On a standard home furnace this would be the G connection.

The other nice thing about the Atwood hyrdoflame 8012 is it's rated at only 1.8A 12V when running, where the larger BTU hydroflame 7000 series uses close to double the amperage. Smaller is better in this case.

Or bigger batteries

[ronstory]

Yes, you are probably right on the cat heater. When I get the heater I'll take a look at the schematic and see if their is a simple way to force the fan to run separtely.

I'm trying to keep with one to two batteries... if it one I'll go flooded lead and if it two I'll probably use a Deka AGM and put them in the closest in the bathroom.

Thanks for all your help.