Improve balanced heat output?

[DustyRoads]

Originally Posted by frlancr

Hello all again...this post is aimed at member Larry-NC...Larry thank you for the clarity on how the furnace could be pulled out without destroying the under-furnace ducting attached. Now that I have all three of those ducts connected back to the furnace (as I noted earlier, one of the ducts was disconnected and laying on the underbelly floor) and am enjoying a measure of heat coming out of all three floor registers I decided to do a little heat gun measuring. The furnace unit, measured at a top back corner of the furnace cabinet, heats up from apprx 90 degrees to almost 150 degrees before the limit switch kicks in and the temp drops back down to 90 ish...this cycle process takes apprx 5 mins (2.5 mins up and 2.5 mins down)...I observed this cycle for about a half hour and it was very consistent. My question to you Larry, as you obviously are pretty knowledgeable on the furnace operation, does this temp range and cycle time seem appropriate. The furnace is a Suburban 30FQ, 3-4 inch ducts to 3 floor registers (two of which are crushed down apprx. 50% due to routing over slide out mechanism) and a 2 inch duct to bath wall sidemount. The plate on the furnace notes maximum (internal?) air temp range, but I don't believe I can accurately measure that with a simple heat gun. Thanks much if you happen to see this post and respond. MC

I would also try resetting the thermostat. I had an issue with the cycling. Once I reset the thermostat all was better.
Let me know if you don't have steps on how to do. It is real easy.

[Larry-NC]

Originally Posted by DustyRoads

I would also try resetting the thermostat. I had an issue with the cycling. Once I reset the thermostat all was better.
Let me know if you don't have steps on how to do. It is real easy.

That implies you have one of those new-fangled digital thermostats with all the fancy gee-gaws.

Both of our trailers have a good old-fashioned two-wire (for heating) mechanical thermostat with the anticipator hidden on the back. There's no way to "reboot" them which is okay because they never need it.

Larry

[DustyRoads]

Originally Posted by Larry-NC

That implies you have one of those new-fangled digital thermostats with all the fancy gee-gaws.

Both of our trailers have a good old-fashioned two-wire (for heating) mechanical thermostat with the anticipator hidden on the back. There's no way to "reboot" them which is okay because they never need it.

Larry

I wouldn't call it fancy. But yes it is digital. It is what comes with a 251rks.

[frlancr]

Thanks Larry et all...will attack TT again today by trying the highest setting on the thermostat, and then actually reading the little manual in order to reset the thermo (anticipator?), if that seems to be the issue...otherwise, I will disconnect all the ducts from underneath the furnace, to eliminate the restrictions in two of the ducts by being crushed down in their route over the slide out mechanism, and let the furnace run un-restricted to see if that stops the cycling. As one poster noted, adding another duct run solved their issue...I'm getting closer to ripping out the entire underbelly and doing clean duct runs, adding some insulation, and resealing with treated panels and cross members for attachment...total PITA just to obtain even heat. MC

[DustyRoads]

Dometic Thermostat System Initialization
A system initialization will need to be performed by the installer after
the system is installed.
• Make sure the Single Zone LCD thermostat is in the Off condition.
See page 4, “Quick Reference To Control Buttons”.
• Press the “+” button and, while holding it, also press and hold
the On/Off Mode button for three seconds. LCD will show
― ― . Press the On/Off Mode button again to turn system off.
This completes the initialization.
The furnace On/Off temperature differential should be set at this time.
See “Mode Description - Furnace” on page 8 for further information
on furnace mode differential setting.

[nayther]

if the discharge temp. is reaching 150 then it is definitely cycling on the high limit. You do not have enough air flow. No doubt, no second guessing that IS the problem. I've fixed two toy haulers with this same issue. Heat anticipator settings (if you have an old analog/bimetal t'stat you might have one but doubtful) will aid in reducing short cycling but won't fix high limit cycling. I tried to live with the issue when I first got our toy hauler but the drain on the batteries and not reaching temp was unbearable in the cold. Once I added another outlet it worked perfect.



By the way I'm 40+ years in the commercial heating and AC business (owner for 10 years), I kinda know what I'm talking about

[frlancr]

Hi again...Nayther I'm sure you are correct that additional duct output is required to bring my furnace down to a normal operating temp. I re-initialized the thermostat yesterday and ran the furnace for about 45 mins, using my heat gun. All ran well for about ten minutes, then the cycling started again...like the previous times...heat ramps up to well over 160 degrees on the cabinet, then gas shuts off and temp drops back down to about 110...process takes about five minutes to ramp up, then down...same as before. I am now planning my attack on the underbelly duct runs and how/where to add an additional run and vent that would help but more heat in the bath/bedroom area. Will require a major undoing of the underbelly to accomplish this. Would like to take this problem to FR for a possible warranty resolve, but given my past experience with trailer warranty claims I know this will be an exercise in extreme frustration without much chance of a satisfactory outcome. Just sad that an otherwise fine trailer product is saddled with this problem due to poor design and manufacture shortcuts. MC

[Larry-NC]

Originally Posted by frlancr

Thanks Larry et all...will attack TT again today by trying the highest setting on the thermostat, and then actually reading the little manual in order to reset the thermo (anticipator?), if that seems to be the issue...otherwise, I will disconnect all the ducts from underneath the furnace, to eliminate the restrictions in two of the ducts by being crushed down in their route over the slide out mechanism, and let the furnace run un-restricted to see if that stops the cycling. As one poster noted, adding another duct run solved their issue...I'm getting closer to ripping out the entire underbelly and doing clean duct runs, adding some insulation, and resealing with treated panels and cross members for attachment...total PITA just to obtain even heat. MC

This is not an anticipator maladjustment. If it were, the entire furnace would go off and on. The condition you have (gas off, blower continues) is a high limit issue. If you want to be 100% sure, put a voltmeter across the high limit switch (easy to find, right in front) and watch it move between 0v and 12v each time the unit high-limits.

As for the duct work, how about having the sheet metal shop make up for you two boxes as follows:
Area of 4" duct = pi *r*r = 3.14 * 4 = 12.4 sq in

So if you only have 3" clearance over the slideout mechanism, you need a duct that's 3" x 4-1/4" or so. That would be an article that transitions from 4" round to 3 x 4-1/4" and back to 4" round. Ideally it would separate in the middle so you could put part through the mechanism from each side. Think of two rectangular funnels where the tops fit together.

If you had only two inches, the rectangular portion would need to be 6-1/4" x 2".

Any good sheet metal shop should be able to make those up for you. (This assumes you cannot just run the 4" ducts below the slideout gear instead of through it.)

Larry

[frlancr]

Yeah, I'm already having some short plenums being made up...only have 2 inches of clearance over the slide out bar, so the 6 x 2 converting to 4 inch on both ends...worst part is the need to basically tear out the underbelly. Have decided to go ahead and replace it with 1/4 inch treated ply panel with runners for attachment...will allow me to add another duct run to better suit the furnace output, clean up crappy work below and add some insulation and provide trap doors in certain areas for easier access...not the project I was anticipating, but should be a much better built TT when I'm done. MC

[SailorSam20500]

On my trailer, I have two runs that go past the slide. Here is a pic of the runs. One runs along the frame, the second has a U in it. Because the slide mechanism is angled, this routing gets the duct to a spot that has sufficient clearance. I put two or three screws into each joint and aluminum taped them. I was surprised how secure the duct runs ended up being.



https://www.forestriverforums.com/fo...4&d=1526570720

[bedubya]

Originally Posted by clarkbre

Following this thread. We have a 247BHDS and the bathroom vent blows extremely well. However, the 3 floor vents are mediocre at best. The front bedroom heat is nearly non-existent.

I've thought about seeing if there is any blockage for the floor vents vs. the bathroom vent.

I wish I had a bathroom vent.

[Larry-NC]

Originally Posted by frlancr

Yeah, I'm already having some short plenums being made up...only have 2 inches of clearance over the slide out bar, so the 6 x 2 converting to 4 inch on both ends...worst part is the need to basically tear out the underbelly. Have decided to go ahead and replace it with 1/4 inch treated ply panel with runners for attachment...will allow me to add another duct run to better suit the furnace output, clean up crappy work below and add some insulation and provide trap doors in certain areas for easier access...not the project I was anticipating, but should be a much better built TT when I'm done. MC

Sounds like we think alike.

Don't forget to take some before and after photos and post them when you are done.

Larry

[swj]

has anyone asked their dealer to look at this as a warranty fix?
or is Fores River doing a soft recall?
My 2018 251RKS has little or no heat in the bedroom????

[SBfishing]

Originally Posted by swj

has anyone asked their dealer to look at this as a warranty fix?
or is Fores River doing a soft recall?
My 2018 251RKS has little or no heat in the bedroom????

Ditto with my 2018 251RKS, heat flow severely diminished in the bedroom. Also notice about a 50% reduction at the second floor register, located about mid-trailer. The small register located at bottom of bathroom vanity (fed by the 2" duct?) has good heat flow.
Wonder how many others have the same issue?

Also, I am a bit concerned of the report of NO INSULATION in the underbelly. I have expandable foam hanging out around water drain holes and a few other fittings underneath, but have not had reason to pull the bottom board off to see what the whole story might be....sounds like we should be checking it out.

Any other Surveyor owners out there want to comment???

[ARICE]

Originally Posted by Larry-NC

Thanks for the education. I did some research and confirmed that you are right: if you restrict the airflow on a squirrel-cage blower speeds up. Loosely, the motor has less work to do stirring the air around the housing than it would actually moving air.

But there's one little thing that's confusing me (as Inspector Columbo would say). In these furnaces there are two independent blowers and air-circuits on the same, single motor. You restrict airflow on the interior air circuit and the motor speeds up. Now you have also increased the rotational velocity of the blower on the combustion air circuit. Wouldn't that move more air through the combustion circuit and keep it cooler? Why would Suburban warn of higher temperatures? Or is there some velocity beyond which the slope of the rotational speed vs air velocity goes negative?

(Would be easier if I could use symbols like lower-case omega here....)

Larry

Think old pickup heaters with squirrel cage blowers. When you closed the fresh air intake (restricted flow) you got warmer air and higher fan speed.
When you opened the fresh air intake (reduced restriction) you got lower fan speed cooler air..
....best analogy I can come up with😁

[Nickrenfro]

We had a 2014 FREEDOM EXPRESS 246RKS--LOVED IT ,but like you said the heat was not even..problem solved--Sold the FE,and bought a 2019 OUTDOORS RV 21FQS ..No problems now !!! Even heat thru-out---bathroom is the same temp also..This TT holds the so well that-- well just get one--the build is superior to everything-even Lance !

[Bdlnky]

Im pretty sure this is supposed to be this way to heat the underbelly/holding tanks