What size furnace?

[Inland RV Center, In]

Originally Posted by pickerdd

From reading through this thread I'm wondering if I made a mistake. I purchased a new NT34SP from Forrest River (that's the company name on the invoice) to replace the original furnace in our '71 Safari, which I'm guessing is a NT20 or NT22. Suggestions?

You had a 20 or 22 thousand BTU furnace.

A very good upgrade would have been a 30,000 BTU furnace.

The 34,000 BTU is OK, but I think a little overkill, especially the additional cost.

Andy

[Lumatic]

On my TW I replaced the NT22a with a NT30. No complaints. I was able to reconnect to the existing NT22a plenum and use the old duct work. It required a little bit of work to get it to fit but not too bad. There are past threads on the subject with excellent photos and instructions.

[fotochop]

Same as Lumatic, I put an NT30 in place of a NT22 and have no complaints about cycling, heat level, etc...You can see it here:

http://www.airforums.com/forums/f427...t22-60035.html

A 19K btu would probably also be fine. I have this crazy dream of one day towing my rig out to Colorado and doing some SKIING! and hey, who knows....

There are many good threads on this, if you scroll to the bottom of the one above you can find a couple more links..

[pickerdd]

Originally Posted by Inland RV Center, In

You had a 20 or 22 thousand BTU furnace.

A very good upgrade would have been a 30,000 BTU furnace.

The 34,000 BTU is OK, but I think a little overkill, especially the additional cost.

Andy

Thanks for the reply Andy. The NT34SP cost $345 including delivery. The NT34SP was about $25 (give or take) more than the NT30SP.

[Over59]

You need a thermostat that you can adjust the anticipator. That keeps the temp more even.

[bhayden]

Originally Posted by Over59

You need a thermostat that you can adjust the anticipator.

All that does is help to prevent overshoot. It does nothing to eliminate the short cycling that occurs with an oversized furnace. Your furnace heats up the heat exchanger to a certain temperature before it starts to blow air. Then it shuts off and the latent heat in the heat exchanger is mostly just lost. The more times per hour the furnace cycles the less efficient it is AND the less comfortable you are. You pay twice, more propane wasted and less even heat.

[Lumatic]

Originally Posted by bhayden

All that does is help to prevent overshoot. It does nothing to eliminate the short cycling that occurs with an oversized furnace. Your furnace heats up the heat exchanger to a certain temperature before it starts to blow air. Then it shuts off and the latent heat in the heat exchanger is mostly just lost. The more times per hour the furnace cycles the less efficient it is AND the less comfortable you are. You pay twice, more propane wasted and less even heat.

When I changed out my NT22 to a NT 30 I had a problem with short cycling. I changed out to the cheapest Walmart thermostat I could find and it solved the problem. There was no anticipator in the OEM stat.

[bhayden]

The cheapest Walmart thermostat is better (for a while) than an old bi-metalic tstat that was malfunctioning; much like the cheapest Walmart tire is better than a 30 year old OEM tire that's leaking air. Better than not working is not a lofty goal. "Cheap" modern tstats are really pretty darn good. It's really not rocket science. Too cold, burn gas; too hot, stop burning gas. Doesn't affect the efficiency of the unit. 1500 watts is about 5k BTU. Most people will find a 1500 watt space heater sufficient in their trailer. I don't think anybody would seriously carry six 1500 watt space heaters around to heat their trailer. Really... that's how absurd it is! Place six electric space heaters around your trailer. Now, make it so that they all turn on full blast at the same time. If that's "comfort" then then you need a 30k BTU furnace.

[GoldFever]

Originally Posted by bhayden

Most people will find a 1500 watt space heater sufficient in their trailer.

I agree with you re: overkill not needed.
My question for this thread is do these Suburban heaters have only one cycle or two? I want / need (our furnace is dead....read: I am tired of trying to get it to cycle on...it does not) to replace ours and I really would rather buy a two cycle (or more?) blower type heater.
Any suggestions? We have a 1992 25foot Excella so it is getting to the point that things are breaking down and need replacing.
Thanks,
Gary

[Jammer]

Originally Posted by bhayden

"Cheap" modern tstats are really pretty darn good. It's really not rocket science. Too cold, burn gas; too hot, stop burning gas.

The newer ones work by adjusting the duration of the heat cycle and are considerably more complex than that. They also lie and pretend that the temperature is right at the setpoint even if it's a degree or two off. Makes people feel more comfortable.

1500 watts is about 5k BTU. Most people will find a 1500 watt space heater sufficient in their trailer. I don't think anybody would seriously carry six 1500 watt space heaters around to heat their trailer. Really... that's how absurd it is! Place six electric space heaters around your trailer. Now, make it so that they all turn on full blast at the same time. If that's "comfort" then then you need a 30k BTU furnace.

I challenge anyone to bring their trailer of any size and construction to my driveway this time of the year and conclude after the first night that a single 1500 watt heater is sufficient.

It really does depend on the trailer size and the weather conditions. We get temps in the teens and a strong wind on thanksgiving some years and in January every year. If the furnace isn't big enough then the trailer is going to be cold and not by just a couple of degrees.

[GoldFever]

BTW, my furnace is an NT30K #2040 with 22,500 Btu out and 30,000 Btu in rating. It measures 13in wide x 9.5in tall x 22in long, front to back. Draws 6.5Amps (ouch!)
If I downsize to the NT 20SE 2.8Amps, it will fit in the space with extra room to spare.
If I go with the NT-30SP 4.5Amps, it will be a tight fit top to bottom.
Smaller is easier and saves energy and I can always add another portable heat unit to the mix as needed.
I do think my decision is staring me in the face.....still....

[bhayden]

Yep, the electrical draw is huge when you oversize. There is nothing good about too much heat. There is a lot of downside.

[bhayden]

Originally Posted by Jammer

I challenge anyone to bring their trailer of any size and construction to my driveway this time of the year and conclude after the first night that a single 1500 watt heater is sufficient.

It really does depend on the trailer size and the weather conditions. We get temps in the teens and a strong wind on thanksgiving some years and in January every year. If the furnace isn't big enough then the trailer is going to be cold and not by just a couple of degrees.

Well, we've lived in our trailer quite comfortably with a 1500W electric heater and the temperature in the upper teens. A strong wind could make a difference but we also had sleeping bags good to sub zero temperatures. Sizing a furnace for nighttime use is silly. As for the day, what are you going to be doing?

We never heat our home above 66 degrees. Usually it's set at 64 during the day and 62 at night. I'd like it at 58 at night but the plans hate anything less that 60 degrees and our heat pump system doesn't do well with recovery temperatures more than 2 degrees at a setting.

[AlumaBorg]

Is there a post on sizing your furnace? I have a 1960 Pacer (16 ft) and it has an old Coleman furnace. I don't know if it was the correct size. I would like to by something new or used and need an idea of what might b ein my ball park for size. I live in Canada but would not likely use it in the dead of winter.
Thanks!

[AlumaBorg]

Oh yeah, I came across this floor furnace from the UK. It would be sweet to use the original floor furnace hole instead of the newer Coleman spot under the sink. Whale RV - Products

[No blenda]

You guys are awesome.
What about for a 16'er? I've got a potential build coming up for a '55 Bubble. Think 10k furnace is enough?

K