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Old 12-31-2009, 09:19 AM   #15
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Originally Posted by garry View Post
You will have a problem with a 2 speed fan there is a safety device in RV heaters that shuts off the gas valve when the fan slows down called a sail switch.
Read my post again, Garry; I only want heat when the theromostat calls for it. The fan on (at a lower speed, and therefore quieter) all the time is to keep the cabin at a more equal temp, but when heat is expected the fan goes to the normal (high) speed.

Two-speed fans are quite common in home forced air systems, but I haven't heard of them in TT installs, so this is a dream at this point.

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Originally Posted by Gen Disarray View Post
A cheap(er) approach is to run a 12v fan or the fan on the AC to keep the air moving.
Rodney,

Cheaper yes, but in my dream, I am not adding another system, I am modifying the existing one. After all, the whole point is just to keep air moving so that the normal tendency of large variations in cabin temp that an on/off fan situation makes are somewhat smoothed out.

The ductwork in the TT is used to keep all areas at one temp, instead of having one part colder than another, which is what our trailer is like now.

Plus, the noise from the AC fan system is like a diesel truck passing through the room. We only use that when it's really hot or humid.
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Old 12-31-2009, 09:20 AM   #16
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Last March I installed an Atwood Excalibur XT two stage furnace. It has cut down the noise and stays on low speed once warmed up. I have used it in 20 deg. nights. I went with a lower BTU (16000 - 22000) even though my trailer had a 25,000 BTU furnace.
No problems with warming up. Seems the low speed is more efficient on propane.
Doesn't wake me up in the night like the old one.

HOWEVER,
I have been working with Atwood on an annoying hum. So far, I am on the second engineer, and they have replaced most components. Next is an Atwood paid new
furnace install, cause they don't seem to be able to find the hum in my unit.

So in January I will report on its progress.
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Old 12-31-2009, 09:28 AM   #17
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Wel duh, it DOES exist! And at pricing that isn't significantly more than the regular single-stage furnace. Here is a link to the one that Hank is talking about above.

Thanks, Hank! Looking forward to your January report.

And thanks too, to Jack for his much better explanation (in post #14 in this thread) of the problem and potential benefits of a two-stage system. AND, another part of the problem, the lack of decent insulation.

cheers,
Aage
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Old 12-31-2009, 10:34 AM   #18
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allrighty now!

yessiree, you guys rock! during my cold stay, the furnace came on and off as stated, and I think that the startup on the motor would actually cause more battery drain than a more constant, low speed operation. I do have an olympian catalytic out in the front of the coach-keeps the front toasty, with no blower, but, I am not sure it would heat the back much? dunno haven't tried that, yet. Obviously, my coach is allllllllmost 25 years young, and from the sound of the furnace blower when it first starts up, it at least needs lubing, or new bearings. So, I like to fix stuff once if possible, and will look at the new furnance XT models very hard. If I gotta yard the existing one out to lube/bearing it, I might just as well spend a few more bucks...afterall, it is the American Way!
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Old 12-31-2009, 10:50 AM   #19
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eight steps to furnace removal

Well, the service manual has a total of eight steps to remove the furnace...reads real easy-there are two steps, that my experience causes a red flag to shoot up, though. So I will see how easy it is...leaving the dang thang together allows me to take spontaneous trips, tho, so I will "sneak" up on it...
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Old 12-31-2009, 11:17 AM   #20
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I also have had the problem of thermostat location. It was in the bedroom, and since I always got up hours earlier than the wife, I was generally too warm in my section with the divider closed. I placed the new thermostat with my XT in the front on the side of the refer. I put four 1 inch rubber standoffs to keep the refer wall from influencing the Tstat. It seems to work well, as I have a thermometer near it, and the air temp is within a couple of degrees of that reading on the Tstat. Also, the bedroom stays cool while my living space is just right.
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Old 12-31-2009, 11:31 AM   #21
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Quote:
Originally Posted by Aage View Post
Wel duh, it DOES exist! And at pricing that isn't significantly more than the regular single-stage furnace. Here is a link to the one that Hank is talking about above.

cheers,
Aage
Hey that's pretty neat. I forgot that a two stage unit, to work truly as it's designed it needs a special thermostat. I found that out on my house. But there may be a work around if you don't want to put in a second thermostat. Some of us have heat pumps so we don't want to throw out our Dometic thermostats which handle A/C, heat pump, and furnace.

I have a Trane two stage high efficiency furnace. After reading the documentation I found out that for those who don't want to install the two stage thermostat, there is a work around.

What the work around is a jumper on the circuit board which will allow you to control the fan speed and burner output by run time. In my case my furnace is jumpered for 5 minutes. The furnace starts up on high mode, but after 5 minutes of run time and if the thermostat is still calling for heat, the unit goes into low stage which cuts the burner output and fan speed. What this means to me is when it really gets cold out and the run time is extended we get the benefits of the low stage. If it's not that cold the high stage takes care of the initial need, but for all intents the house will hold temp for quite a while so run time is minimal. I know doing it like this saved me $350 rather than putting in the two stage thermostat.

Typically a two stage thermostat determines how far the inside temperature is from the set point. Let's say it triggers at 5 degrees. So if the interior temperature is less than 5 degrees from the set point, the furnace runs on low stage. If it is 5 degrees or more (wake up time for example), the unit will kick into high mode till it gets below that 5 degree threshold, then it kicks the furnace down to low stage to get to set point.

If you think about it I know the Dometic Heat Pump/AC unit on my Classic has a similar feature when you set the fan to Auto. It doesn't control the compressor but it does adjust the fan speed. Too far from the set point the fan comes up on high, close enough it comes up on low. Problem is it's useless in a hot clime since you could be nice and cozy in the morning but once the daytime heat builds, the lower speed setting is insufficient to maintain temperature. Problem is the spread for the fan to kick in on high is way too wide and you get uncomfortable waiting for it to finally kick in. I like the auto setting since it will shut the fan down once you reach set point. This keeps the fan from redistributing the water on the coils that collect during the cooling cycle back into interior when the compressor is not running.


Now when the home A/C unit fails, I'll probably put in a two stage A/C compressor. At that time it may make sense to upgrade the thermostat.

Jack
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Old 12-31-2009, 11:58 AM   #22
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Hey Aage, I got to thinking about your 2 speed fan in post 15. Maybe adding a 2nd fan in the duct could be the answer to constant circulation. I've seen in the home improvement stores a fan that mounts inside the ducts to move air to rooms further away from the furnace. Unfortunately they run on 110 v ac.

Later thoughts led me to my AS fridge. I've installed a small, low power draw 12 v dc computer fan to increase air circulation there. Hmmmm....... I wonder if I could put the same fan between the duct & wall vent. Of course I'll need to have a switch to control fan when not needed. the only bad thing I can see so far is the reduction of air flow in the 1 of the 3 vents coming out of my furnace. Is the sail switch located in the inside air or the burn air side of the furnace?

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Old 12-31-2009, 04:19 PM   #23
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a temp sensor for a 12v automotive fan might work. you'll just need to find one that closes before 200 degrees! maybe a cooling temp sensor would do the trick. a guage sender would even provide variable speed :-)
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Old 12-31-2009, 04:53 PM   #24
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Is there a way to reduce furnace flame, full blast for short burst adds to the noise and requires fan to operate at high speed to stop meltdown?
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Old 12-31-2009, 10:23 PM   #25
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Ricky, Ricky, & Dave,

Nawww, no experimenting for me.

I'm just gonna wait till spring and see if the budget will withstand a nice new Atwood Excaliber XT, and, assuming that it does, and assuming too that Hank's results with the hum problem turn out well, I will get one installed.

I'll horse around with a lot of things, but the innards of a furnace? No way, José!

Say, does anybody think that the Hank's furnace only hums because it doesn't know the words...?
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Old 12-31-2009, 10:23 PM   #26
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Another thing to consider, if customizing, is the installation of a smaller furnace, such that it is controlled by the first stage of a two stage thermostat while the existing furnace is controlled by the second stage.
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Old 01-02-2010, 09:14 PM   #27
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Glad to see the XT info, and I also look forward to more. Excellent thread!
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Old 01-02-2010, 09:46 PM   #28
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Changing out the OEM thermostat to the cheapest Walmart unit solved my short cycling problem. The thermostat said 24 volts but works just fine on 12.
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