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Relocate the furnace inlet grill and block off that opening?


John E Davies

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Old thread but new data for chewing on:

I installed a sensor hanging next to the water pump under the curb side bed and one at the furnace thermostat.

The data below is taken across a full day while outside night temps are in the low 30f range and we set the furnace to heat living space to 62F at night.

I set a threshold at 100F for the water pump belly sensor and you see the time between 12am and 8am that  belly temps hit > 100F as the heater cycles on and off while maintaining 58-62f in the cabin. (Thermostat sensor).  

I’m curious if this is normal for that the space  under the bed is 40F hotter than the main cabin?

Craig

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2019 Elite II (Hull 505 - Galway Girl - August 7, 2019 Delivery) 
Tow Vehicle: 2021 F350 King Ranch, FX4, MaxTow Package, 10 Speed, 3.55 Rear Axle
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9 hours ago, Galway Girl said:

I’m curious if this is normal for that the space  under the bed is 40F hotter than the main cabin?

I haven't ever seen anything like that in our 2020 Oliver and I have always had 9 temp sensors located throughout the trailer.  I took some "baseline" temps all around the trailer in 2020 before I made some HVAC changes and I was seeing temps under the curbside bed in the low 60's when it was in the 20's outside and the inside temp was set at 70.  I still have the data / graphs.

It seems to me like something "abnormal" is causing an excessive heat buildup under your curbside bed when your heat is running.  Maybe one of your ducts has a hole in it and it's pushing the hot air right at your temp sensor?

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16 hours ago, Galway Girl said:

I’m curious if this is normal for that the space  under the bed is 40F hotter than the main cabin?

If your 2019 LE II is the standard bed model (like my 2020), then yes, it is (unfortunately) normal and reflects a design flaw on Oliver's part.  I would speculatgethat NCeagle's 2020 LE II has the twin bed option which would explain why NCeagle hasn't observed the same phenomena. 

In our particular vintage of LE II's, Oliver placed only a single air return duct in the very back on the curbside immediately in front of the furnace.  When the standard bed is set up and the furnace is running, most of the hot air blowing out the supply ducts can't escape the cavity under the bed and is immediately pulled back through the return duct and into the furnace.  This hotter air into the furnace in turn causes the supply air temperature to become even hotter which in turn causes hotter return air into the furnace which increases the temperature of the supply air, etc.  Meanwhile, the air temperature in the cabin takes forever to increase because the hot air from the supply vents is immediately pulled back into the furnace and doesn't mix well in the cabin.  As the intake air around the furnace (i.e., water pump) gets hotter, the heat exchanger in the furnace gets hotter and eventually overheats and triggers a safety shut-down of the furnace flame before the cabin actually reaches the temperature set point; referred to as short-cycling. 

From your pictures, it looks like your furnace started short-cycling badly when you increased the thermostat set-point just before 8 in the morning.  It appears that it took over an hour to raise the cabin temperature by 10 degrees quite probably due to the short-cycling. 

I doubt this is an issue in the twin bed model because the hot air from the supply vents can freely mix into the cabin air and doesn't get trapped under the bed to be fed immediately back into the furnace.

The quick fix for standard bed owners is to open another furnace return vent on the street side of the trailer forward of the bed.  This helps pull hot air out from under the bed and returns that hot air to the furnace via the street side basement opening and over the water tanks.  My 2020 LE II has a nice round access hatch on the streetside below the pantry (to access the Inverter GFCI).  In the heating season, I just remove that access cover to that streetside hatch and the short cycling problem is solved, the furnace runs quieter, basement temps are more even throughout, and the furnace/thermostat do a much better job keeping a constant temperature at the set point chosen.

 

 

 

 

 

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Steve and Lornie

LE II Standard  Hull #657  2004 4Runner 4.7 L V8

Oregon

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Chukarhunter, I was considering installing an additional cold air return also. Do believe the location directly below the pantry is the best location or would consider a differnt location if you did not already have the access port? Thanks.

2022 Oliver Legacy Elite II, Hull 1242, 9/26/22

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Tow with Supercrew Cab 2019 F-150 4 x4, 5.0L 4-Valve V8 with 3.73 axle ratio & 157" wheelbase.

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Gliddenwoods,

If I didn't have the access port below the pantry, I would probably add a second return vent even farther forward, probably under the forward dinette.  That is because I believe return vents should be placed as far as reasonable from the supply vents.  This causes the best mixing of warm supply air as it is pulled across the cabin and into the return vent, and also causes the best mixing of warm cabin air throughout the basement on its way back to the furnace intake.  It is important to have warm return air-flow flowing across as much of the basement as possible on the way back to the furnace to eliminate dead air spots which can become very cold in sub-freezing weather.

Another easy way to add some "as needed" additional return paths for warm cabin air into the basement is to slightly open a drawer or two.  Since the wall behind the drawers is open to the basement, cracking open one or more drawers by an inch or less will provide another path for warm cabin air to be pulled into the basement, warming the sink plumbing at the same time.

The best solution I believe is to provide a decent sized return vent in the bathroom which will allow warm cabin air to warm the entire length of the cabin as it is pulled into the bathroom and also the entire length of the basement on the way back to the furnace intake vents.  I believe that Oliver started putting in a return vent in the bathroom in 2022 (although I think  it is very small). 

After three years of patient observation of my furnace's performance under all sorts of weather conditions using multiple thermometers, I have decided to add a return vent to the bathroom but not cut any new holes.  Instead, I am disconnecting the bathroom flexduct supply hose from the existing supply vent in the bathroom which will turn the existing supply vent into a return vent.  I will re-terminate the flex duct supply hose inside the vanity in the front of the basement which will place warm air directly under the bathroom and closet; common cold spots.  The combination of warm air flowing across the cabin and into the bathroom and then into the basement and back to the furnace should make the cabin and bathroom more comfortable and substantially reduce the temperature differentials between the cabin and basement.

I have multiple remote thermometers and will report on the results of my simple modification after thoroughly testing it this winter.  The good thing is If it doesn't work satisfactorily, I can easily restore everything to its original configuration and try something else.

 

 

Steve and Lornie

LE II Standard  Hull #657  2004 4Runner 4.7 L V8

Oregon

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12 hours ago, Chukarhunter said:

If I didn't have the access port below the pantry, I would probably add a second return vent even farther forward, probably under the forward dinette. 

Like this?

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12 hours ago, Chukarhunter said:

The best solution I believe is to provide a decent sized return vent in the bathroom which will allow warm cabin air to warm the entire length of the cabin as it is pulled into the bathroom and also the entire length of the basement on the way back to the furnace intake vents.  I believe that Oliver started putting in a return vent in the bathroom in 2022 (although I think  it is very small). 

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Like this bathroom return air vent (viewed from underneath the forward dinette seat opening in our 2022 Elite II)?

They have significantly improved heated air circulation in our Elite II, and helped keep the "bilge" area warmer in cold weather.

I agree that the solution is not relocation of the primary return air vent, but addition of more return air vents in the forward area of the trailer, particularly the bathroom.

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On 10/14/2023 at 10:28 AM, Chukarhunter said:

doubt this is an issue in the twin bed model because the hot air from the supply vents can freely mix into the cabin air and doesn't get trapped under the bed to be fed immediately back into the furnace.

The data shown is from our twin bed model. 

2019 Elite II (Hull 505 - Galway Girl - August 7, 2019 Delivery) 
Tow Vehicle: 2021 F350 King Ranch, FX4, MaxTow Package, 10 Speed, 3.55 Rear Axle
Batteries Upgrade: Dual 315GTX Lithionics Lithiums - 630AH Total
Inverter/Charger: Xantrex 2000Pro 

Travel BLOG:  https://4-ever-hitched.com

 

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I’m turning in a service ticket on this issue of short cycling and extreme temps in belly.  

2019 Elite II (Hull 505 - Galway Girl - August 7, 2019 Delivery) 
Tow Vehicle: 2021 F350 King Ranch, FX4, MaxTow Package, 10 Speed, 3.55 Rear Axle
Batteries Upgrade: Dual 315GTX Lithionics Lithiums - 630AH Total
Inverter/Charger: Xantrex 2000Pro 

Travel BLOG:  https://4-ever-hitched.com

 

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12 hours ago, Galway Girl said:

I’m turning in a service ticket on this issue of short cycling and extreme temps in belly.  

Looking at the thermostat temperature data during the over-night period after stabilization when there is likely very little activity i.e., door/window opening, movement etc., the control looks pretty good. It looks like single-cycle variance of the thermostatic control
algorithm is approximately 2 degrees with a cycle period of approximately 30 minutes per cycle consistently throughout the over-night; pretty good. The average temperature over the entire over-night control period is very consistent with negligible wanderation suggesting good control. I doubt that my house control is that good. 

It’s hard to say what factors influenced the data prior to and after the over-night periods, possibly activities within the trailer; hard to say. 

I’m not sure what would cause the temperatures to be what they are inside the equipment bays, it might be interesting to see what the skin temperature of the furnace itself is as it may be radiating heat towards the water pump area. 

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Tom & Doreen • 2023 Elite ll • Hull #1321 • 2023 Tundra Platinum Crew Max • Cheshire CT 

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12 hours ago, Galway Girl said:

I’m turning in a service ticket on this issue of short cycling and extreme temps in belly.  

A potential source is that one or more of your ducts have come apart.  This happens often in flex duct applications.   

GJ

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