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Old 08-26-2013, 05:31 PM   #1
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Atwood Two Stage Furnace.

I really like the idea of a two stage furnace. They run in high until reaching the set temperature and then switch to a lower burner and fan setting. Atwood has them that are the same size as the 8500 series

What I'm wondering:

It looks like you need to use their digital thermostat which would require removing the Dometic CCC2. Has anyone done this mod? Any problems hooking up to the Dometic AC?
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Old 08-26-2013, 05:49 PM   #2
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Sounds like these run differently than home 2 stage gas furnaces. Typically a home 2 stage furnace starts on stage one (assuming it's a normal call for heat). Stage 2 (high heat) is only called for when either the difference between the set point and the inside temperature is 4 degress or more, or if the furnace runs over a certain length of time, and is either gaining little or no ground in raising temperatures. Typically 2 stage gas furnaces do not save fuel. The idea is more of a comfort level with no blasts of hot air.

In an RV I'm assuming that that concept probably doesn't work as well. In our Classic we tend to use the heat pump as our first line of warmth. Eventually as it gets colder outside we find that it takes too long to get comfortable. Probably a lot has to do with the single pane glass and the minimal wall insulation which radiates the cold.

I'm assuming you don't have a heat pump in your trailer. You would probably have to verify with Atwood that their thermostat can support the telephone jack wiring mode used and can provide some of the features of the CC2. For example if you use the auto setting on the CC2, the fan speed of the Dometic air conditioner varies by the difference in the set point temperature and the inside temperature. This allows for high speed activation of the fan when the trailer is hot, usually when you set up. Vice versa it does the same in heat pump mode. We usually use auto since I like the fan to shut down when the set point is hit. Especially in the summer where continual fan running increases the humidity at night and gives you a cold clammy comfort level.

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Old 08-26-2013, 05:55 PM   #3
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I have a heat pump. But I really don't like using it because of the noise, and also when boon docking it's not available. I find that the furnace works well but the on and off cycling has inherent temperature fluctuation. Going to low mode would moderate that.

The Atwood thermostat uses RJ 45 cable. I'm not sure but I think the Dometic is RJ 6.

This isn't something I'm looking at doing right away. It's just another item on my very long wish list.
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Old 08-30-2013, 10:13 AM   #4
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I guess no one has done this. My big concern is that the thermostat for the 2 stage Atwood doesn't look like it supports the Dometic heat pump.

The idea behind this one is that for initial warmup it runs 2 burners and high speed fan until getting close to the set point and then switching to one burner and low speed fan. Less noise, less temperature fluctuation than the off/on cycling of the single stage.
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Old 08-31-2013, 07:30 PM   #5
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Hi Dave

There's another Airforums member who installed an early Atwood 2-stage and had noise problems with it. Might want to check around, although it's not clear whether Atwood is still using the same design.

I would suggest using a separate thermostat for the Atwood furnace and the Dometic heat pump. There isn't really any benefit to having them combined. I have the Dometic CCC and want to rip it out and replace it with something less complicated every time I use it.
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Old 08-31-2013, 09:18 PM   #6
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Quote:
Originally Posted by Jammer View Post
There's another Airforums member who installed an early Atwood 2-stage and had noise problems with it. Might want to check around, although it's not clear whether Atwood is still using the same design.
I was trying to think of that member's name too. He got -very- involved with Atwood one it, because he wasn't happy at all with it. Atwood was very open to working with him but in the end he returned it. I think that noise was one issue, but that wasn't all of it IIRC.

Good luck with your search. I too loved the theory of the 2-stage idea, and while this has been standard in home models for years, apparently it just wasn't ready for prime time in TTs.
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Old 08-31-2013, 09:46 PM   #7
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Thanks for the info. Hard to believe it would be any louder than the one I have.
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Old 08-31-2013, 10:18 PM   #8
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I found the thread. Hank put in the Excalibur two stage in 2009. His experience, although the fan noise was less he had a hum when running at low speed. It would be nice to know if Atwood has fixed the problem in 4 years.
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Old 09-01-2013, 08:19 AM   #9
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Congrats on finding the thread.

Perhaps if you emailed Hank, he could give you the engineer's name he dealt with at Atwood, or contact him for you to see if your question was ever answered...
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Old 09-01-2013, 05:06 PM   #10
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Quote:
Originally Posted by Aage View Post

I was trying to think of that member's name too. He got -very- involved with Atwood one it, because he wasn't happy at all with it. Atwood was very open to working with him but in the end he returned it. I think that noise was one issue, but that wasn't all of it IIRC.

Good luck with your search. I too loved the theory of the 2-stage idea, and while this has been standard in home models for years, apparently it just wasn't ready for prime time in TTs.
I think the Atwood works opposite the way home 2 stage units work. Probably due to the fact that the heat loss is so great in a trailer that you need the initial output to quickly recover the temp.

Jack
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