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Old 12-13-2011, 06:59 PM   #1
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Catalytic heater vs. furnace

okay here are a couple of questions and concerns.....
regarding a catalytic heater and a suburban furnace
Which uses more propane, is more efficient?
Which is safer to leave running during the night?
carbon monoxide?
the lp gas alarm begins when the furnace turns on.
below freezing temps is when these are used at night to protect the water lines and stay comfortable.

All information is appreciated
hoosiergypsy
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Old 12-13-2011, 07:22 PM   #2
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There will be lots of input on this topic. Here is mine.

A catalytic heater is probably more efficient in terms of propane use. More of the heat it produces heats the objects in front of it, and not the air around it.

A furnace will burn more propane, and use energy to run the fan, but it will make the entire trailer warmer quicker. Yes, there are ducts pointed at the holding tanks, but, a trailer warmed with the catalytic heat will radiate some heat to the tanks.

Tanks not freezing are more a function of how cold it is where you are.

Boondocking, a catalytic heater is easier. I have used one when outdoor temps are in the single digits and stayed warm enough.

The furnace takes a lot of battery power to run the blower. About one really cold night will have the batteries dead. However, if you are hooked to electric power, the furnace will keep the trailer nice.


Good Luck,
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Old 12-13-2011, 08:00 PM   #3
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Yeah, exactly what "jdalrymple " said.

I will add that we have found when we do have full hookups, we use small cube heaters, without full hookups the furnace is a battey killer so we use the cat heater. We have only fired up the central heat once in the last 2 years.

Our '63 we are rebuilding will not have a central heat for just those reasons.
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Old 12-13-2011, 09:40 PM   #4
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It is dangerous to use catalytic heaters without ventilating the trailer to replace the oxygen they use in combustion, who knows how much? I don't like sharing my oxygen supply with them.

There are safer alternatives, the furnace, heat pump, and electric space heaters.

doug k
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Old 12-13-2011, 09:56 PM   #5
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Originally Posted by dkottum View Post
It is dangerous to use catalytic heaters without ventilating the trailer to replace the oxygen they use in combustion, who knows how much? I don't like sharing my oxygen supply with them.

There are safer alternatives, the furnace, heat pump, and electric space heaters.

doug k
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Old 12-13-2011, 10:23 PM   #6
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Quote:
Originally Posted by HoosierGypsy View Post
okay here are a couple of questions and concerns.....
regarding a catalytic heater and a suburban furnace
Hello Hoosier

Well let's take these one at a time then.

Quote:
Which uses more propane, is more efficient?
Suburban furnace typically 75% efficient. Catalytic heater typically 98% efficient. But to run a catalytic heater safely requires you to leave a window open which more than overcomes the difference in efficiency.

Quote:
Which is safer to leave running during the night?
Suburban furnace unless there's something bad wrong with it
Quote:
carbon monoxide?
Well it's like this.

Catalytic heaters produce very little carbon monoxide when new but as the catalyst degrades over time the amount of carbon monoxide they generate gradually increases. And, it is emitted directly into the interior of the trailer, where you breathe it. In general it is not economically feasible to replace the catalyst so it becomes a matter of how much carbon monoxide you are willing to breathe before you replace the whole heater.

A suburban furnace has a heat exchanger so any carbon monoxide it generates will be blown outside, where it doesn't matter much, until the heat exchanger rusts out and fails, which takes a long time. Once the heat exchanger fails, the entire furnace should be replaced.

Quote:
the lp gas alarm begins when the furnace turns on.
Then there's something wrong with the furnace and you should fix it before you use it any more. Furnaces that work properly don't leak propane.
Quote:
below freezing temps is when these are used at night to protect the water lines and stay comfortable.

All information is appreciated
hoosiergypsy
Other facts to consider

1) Catalytic heaters produce less heat and will not work well enough in really cold weather. Maybe down to 40 degrees or so depending on the size of the heater and the size of the trailer.
2) Catalytic heaters produce a fair amount of water vapor which will tend to condense on the walls and elsewhere and create a variety of problems, mold, etc. This is more of a problem at lower temps and with extended use than it is for the occasional 55 degree night
3) Finding a safe place to mount a cat is something of a problem because of the clearances required. To do it right you have to keep it away from any kind of combustibles - table cloth, curtains, bedspread, and there aren't very many places that qualify. Usually people mount them right by the outside door.
4) There's no ductwork so distribution of heat becomes a problem. Often furnaces are installed without enough ductwork but at least the idea is there.
5) The only real benefit of a cat is that they don't require any electricity to run so they appeal to people who boondock in cold weather. The suburban furnace uses electricity and when all you have are batteries it can run them down in 1 or 2 cold nights. But there are other safer alternatives available, though, look for my threads on the topic in the furnace & air conditioning section of this site.

Hope this helps

Jammer
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Old 12-13-2011, 10:27 PM   #7
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A catalytic heater runs at about 5,000 8,000 BTU/hr and the furnace about 20,000 to 30,000 BTU/hr (a gallon of propane is about 93,000 BTU)

The catalytic heater is 'always on' and relies on conduction and radiation to disperse its heat. The furnace is forced air and runs on a duty cycle depending upon the thermostat call.

The catalytic heater is not (usually, most models) vented which means all combustion products remain in the trailer unless there is proper ventilation. Note that this isn't only CO2 and CO but also water vapor, which can be a problem.

The furnace uses a vented combustion which reduces its efficiency some but keeps all combustion products outside.

The furnace needs about 100 watts of electricity to power its fans and controls. (batteries have about 12 watt hours per pound so the typical trailer may have a bit over a kilowatt hour available)

When the propane tanks get cold, they can't 'boil off' gas very fast so that might be a problem trying to run both the furnace and the water heater and the oven in very cold weather depending upon your tank size.
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Old 12-13-2011, 11:28 PM   #8
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I'd rather use one of these, since it avoids the excessive electricity consumption and noise of the forced air furnace.


Dickinson Newport Propane Boat Heater / Fireplace, P12000, Dickinson Marine's largest propane model, is ideal for boats up to 30/36 ft. The combustion process is completely isolated from the inside of the boat by the unique, direct vent design. A built-in blower provides good heat circulation for your boat.
  • Bulkhead mounted boat heater / fireplace
  • Non-rust stainless steel construction
  • Unaffected by motion, winds or weather conditions
  • Fuel Consumption: Low 1 lb - 5.5 hrs, 20 lb - 110 hrs, High 1 lb - 3.9 hrs, 20 lb - 78 hrs
  • Heat output for the P12000 is 7,000 - 9,700 BTU
- Bart
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Old 12-14-2011, 12:40 AM   #9
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Lots of real good info here and I agree with all of it. Bryanl- If the furnace requires a 100 watts and the average trailer may have 1 kw-hr of energy available, I guess that means that you can run the furnace about 10 hours (constant) before the batteries are depleted. Is this correct? Taking this one step further if the typical cat heater puts out about one third the heat of the furnace than the furnace only needs to run one third of the time to put out the same heat as the cat heater. So instead of running the cat heater for 10 hours you run the furnace for 3.33 hours. Then the batteries will make it for 3 days (comparing apples to apples- same heat output).

I will only add that all the cat heater manufacturers that I am aware of specifically state that you should not operate the cat heater when you are sleeping. With that kind of warning, I don't think that I would sleep very well with one operating. I would rather just run the furnace and recharge the batteries in the morning with my 1,000 watt Honda if it is needed.

Dan
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Old 12-14-2011, 07:42 AM   #10
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TouringDan

The battery life question is important enough that a detailed trailer-specific answer is worth getting rather than rules of thumb.

Furnaces vary in their power consumption from one model to the next with the ones in Airstreams using anywhere between 5 and 12 amps. Battery installations vary with trailers having one or two 90 aH batteries in a stock configuration with many people adding extra. In my trailer I have 180 aH of batteries and the furnace draws 10 amps so the max I can run the furnace is 18 hours. In practice I find I can run it for one overnight stay.

Cat heaters generally don't use any electricity at all, which is the reason people like them.

Barts mentions the Newport heaters which are one of several alternatives which I compare here:

http://www.airforums.com/forums/f427...ers-72237.html

And here are a couple more to consider that are intended for residential use. I'm not aware of any successful Airstream installations. They're vented gas heaters that don't use a fan:

http://www.airforums.com/forums/f427...ity-74936.html
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Old 12-14-2011, 07:58 AM   #11
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I like the Boat heater above because it also has a purdy flame, a bit pricy as is most boat stuff.

New cats should have an auto O2 or CO sensor which shuts it down before it croaks you.

I have been having the cat heater debate with myself for a couple of years, and since I have a Honda 2000 inverter genny the batt depletion argument is nil. I can also use it to power a small ceramic heater.
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Old 12-14-2011, 10:50 AM   #12
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A final fact to consider is that many people who do cold-weather boondocking don't heat the trailer at night, instead relying on sleeping bags for comfort. It's then only necessary to run the furnace for a relatively brief time in the morning and evening.
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Old 12-14-2011, 11:13 AM   #13
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When the propane tanks get cold, they can't 'boil off' gas very fast so that might be a problem trying to run both the furnace and the water heater and the oven in very cold weather depending upon your tank size.
Maybe with trailers,but we've been below zero many times and had no problems. I do miss the CAT heater we had in our former Excella trailer, though.
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Old 12-14-2011, 11:25 AM   #14
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A final fact to consider is that many people who do cold-weather boondocking don't heat the trailer at night, instead relying on sleeping bags for comfort. It's then only necessary to run the furnace for a relatively brief time in the morning and evening.
Cold is a relative temperature, but to me it means below freezing. I'm surprised it doesn't mean that to someone from Minnesota.

I would be very apprehensive about the plumbing without heat below 32F. It will definitely freeze at some point in time. I guess one could hope it will not freeze before you turn the furnace on again in the morning.

I agree with Jammer's earlier post about the alarm going off.

That is not normal and could indicate a serous problem. I would recommend finding and fixing it, whether it is the furnace or the alarm.

Ken
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