My DW has asked if I can improve the airflow in the trailer now that things are starting to cool off here in Michigan and we're using the furnace. The heating unit blows air well in the trailer and keeps the central part of the trailer well heated, but the ends of the trailer (bathroom & bedroom) have 2" flexible ducting that T's off from larger size ducting (I believe 5" diameter)and there's minimal airflow with the smaller tubing. I was wondering if anyone has replaced their "T" fitting with a "wye" fitting and if that increased the airflow through the smaller ducting? I've read about the dangers of restricting airflow, but thought the "Wye" fitting might actually increase airflow as long as I maintain the original larger output. Any thoughts or successful mods to solve this minor issue?

on my trailer they used the corrigated metalized mylar for ducts. One, they have lots of airflow resistance and two, not much insulation. I dropped the underbelly and replaced all of that with the same diameter rigid snap together ducting and then wrapped it all with a few layers of the adhesive backed foil insulation.massive improvement in airflow and temperature.

Yes it is possible to redo your heat duct and vents. The difference between a 2"duct and a 4"duct is that the 4" has four times the inside area that a 2" has, and that is why your bath and bed area are cold.On a previous 5th wheel trailer that I had, there was 2" dia. duct in the step area aimed away from the sleeping area. Which I thought was quite dumb. I changed it to a 4" duct and located the outlet in the sleeping area for a big improvement. On my current 5thwheel they never put a heat and AC vent in the bathroom, so I added both to bath. With the way that MFG. do things in RV's, I wonder if any of the designers have eve used one.

I had to redo my ductwork, eliminating five 90s and eight feet of duct, I don’t no who,designed this heating system, but they head their head up their a@&. It made a huge difference on even heat with less propane......

rstanek wrote:I had to redo my ductwork, eliminating five 90s and eight feet of duct, I don’t no who,designed this heating system, but they head their head up their a@&. It made a huge difference on even heat with less propane......Many points of leakage, foil duct tape is your best friend. Look at the connection at the furnace it's self, if connected to a floor duck that connection is not very loose.

You guys are making think it might be worth dropping my underbelly, and re-doing our ducts as well. The only thing worse than the airflow ( or lack thereof), is the noise. Man, is the fan ever noisy!

Heating duct airflow improvement | Good Sam Community

ktmrfs
Explorer II
Oct 05, 2017
campigloo wrote:
When you went to the rigid duct did you allow any way for some warm air to warm the underbelly? Did it seem to make any difference either way?

what I did was to use a hole saw to cut a 1/2" dia hole in the side of the floor vent nearest the holding/fresh water tanks. running a cheap remote sense thermostat into the underbelly so far indicates that the underbelly stays about 10 degrees F cooler than the trailer when the heat is on. plenty warm to protect the tanks from freezing.

even that small hole will duct a noticeable amount of warm air into the underbelly. Think how much loose connections and/or other holes in ducting can do
time2roll
Nomad
Oct 05, 2017
westend wrote:
I don't use the typical RV furnace but I'm curious about one thing--you folks that are increasing duct size or flow rates, do you notice less airflow in ducts that were not modified? Has the temp coming from the unaltered registers and ducts as hot as before modifying any heat runs?
I'm just curious about this, no ill will intended.
Ok on my 26' foot trailer OEM three floor vents down the middle. The duct is boxed aluminum about 2" x 10" and was installed poorly and rather restricted. Bathroom was very warm and the main area with two openings was very weak.

Added the two more ducts just short and easy to the main area. Sure there is less through the original ducts but still tons more heat exactly where it is needed. Can now leave the bathroom door closed.
ktmrfs
Explorer II
Oct 05, 2017
westend wrote:
I don't use the typical RV furnace but I'm curious about one thing--you folks that are increasing duct size or flow rates, do you notice less airflow in ducts that were not modified? Has the temp coming from the unaltered registers and ducts as hot as before modifying any heat runs?
I'm just curious about this, no ill will intended.

no actually airflow increased overall and temperature increased on the end ducts. Why? the typical metalized mylar spiral wire wound ducting has much higher airflow resistance than a 4 inch metal ducting.

Now I did replace all the ducting with 4inch metal ducting and insulated it.
westend
Explorer
Oct 05, 2017
I don't use the typical RV furnace but I'm curious about one thing--you folks that are increasing duct size or flow rates, do you notice less airflow in ducts that were not modified? Has the temp coming from the unaltered registers and ducts as hot as before modifying any heat runs?
I'm just curious about this, no ill will intended.
Huntindog
Explorer
Oct 05, 2017
I added a 4" vent in my bunkhouse. I was able to utilize one of the unused outlets on the heater box. Cut a hole it the wall, and it blows more heat than needed, so I installed an adjustable vent to regulate the temp. It was a fantastic fix for a previously cold BH.
campigloo
Explorer
Oct 04, 2017
When you went to the rigid duct did you allow any way for some warm air to warm the underbelly? Did it seem to make any difference either way?
time2roll
Nomad
Oct 04, 2017
I would go all 4" if you can. I added two 4" ducts to mine due to poor airflow causing the furnace to cycle on the high limit switch. More airflow can only be better IMO.
FLY_4_FUN
Explorer
Oct 04, 2017
My main duct running under our bedroom had 2/3 cut away/blocked as they ran a 1.5" grey line through it. Best I could do was remove their blockage and insulate the line where it runs through the duct. Now more hot air flows around the pipe and as a side benefit our furnace high limit switch doesn't shut the unit down. About the poorest engineering I have ever witnessed in the 4 rigs we have owned.
WolverineState
Explorer
Oct 04, 2017
Thanks for all the replies. I measured the duct size last night and it's 4" with a 2" duct at the T fitting. Not much more than a light breeze gets thru the 2" ducts.
Sine no one sells a 4x4x2 wye connection, I'm buying a 4x4x4 wye at home depot with a 4x3 reducer and upping the size of the smaller ducts to 3". All I need now is a free day to do it.
nohurry
Explorer
Oct 04, 2017
You guys are making think it might be worth dropping my underbelly, and re-doing our ducts as well. The only thing worse than the airflow ( or lack thereof), is the noise. Man, is the fan ever noisy!

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