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Old 02-13-2019, 12:31 PM   #1
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Improve balanced heat output?

Greetings all...I have a 2018 Surveyor 251rks...generally pleased with TT, except for terrible heat balance out of the four heat vents...FR chose to run one 2 inch duct from the 30K Suburban furnace to feed the four vents, with about 80% of the heat coming out of the first vent a couple of feet from the furnace, even though the furnace instructions clearly call for a minimum of 3 four inch duct runs for this size furnace. My only fix is to use the 2 four inch knockouts that I can access on the side of the furnace and run 2 three or four inch duct runs through the floor and feed the four vents in a two and two split with probably an air balance damper on one of the runs to create an optimum balance...this requires dropping the colorplast plastic underbelly for access...my question: who has attempted this project and what unanticipated pitfalls, besides lots of swearing, did you encounter in routing the duct runs around tanks, electrical, etc. Thanks for any comments and tips...Mike C
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Old 02-13-2019, 12:46 PM   #2
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Originally Posted by frlancr View Post
Greetings all...I have a 2018 Surveyor 251rks...generally pleased with TT, except for terrible heat balance out of the four heat vents...FR chose to run one 2 inch duct from the 30K Suburban furnace to feed the four vents, with about 80% of the heat coming out of the first vent a couple of feet from the furnace, even though the furnace instructions clearly call for a minimum of 3 four inch duct runs for this size furnace. My only fix is to use the 2 four inch knockouts that I can access on the side of the furnace and run 2 three or four inch duct runs through the floor and feed the four vents in a two and two split with probably an air balance damper on one of the runs to create an optimum balance...this requires dropping the colorplast plastic underbelly for access...my question: who has attempted this project and what unanticipated pitfalls, besides lots of swearing, did you encounter in routing the duct runs around tanks, electrical, etc. Thanks for any comments and tips...Mike C
Sorry I am no help to you. So far we have not had to use the furnace since we bought the 251rks in 2016. Hoping that will change this year.
I will reach out to you or will look for updated posts from you.
Good luck!!
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Old 02-13-2019, 02:09 PM   #3
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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.
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Old 02-15-2019, 09:07 PM   #4
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Balanced heat output

Hi all...I'm replying to my own thread...I have discovered some interesting things in the last day or so...first, I stated that there was only one 2 inch duct hose exiting the furnace on my 251RKS...this is incorrect...after pulling down a section of the underbelly across from the furnace I was able to see what is not obvious...bottom line: there is a rectangular knockout on the bottom of the furnace, hidden from view, and punched through the floor below where the furnace sits is where three 4 inch duct hoses are connected to run to the three floor registers...pity the poor person who has to pull the furnace out for service, as you will destroy the duct hose connections...you must open up the underbelly under the furnace, which I did, and found that one of the 4 inch duct hoses was NOT connected. Huge PITA to reconnect this duct, as there is zero room to get the hose clamp on and tighten...probably why it fell off in the first place...will try a short sleeve extension that I can press fit on and hope to squeeze some hvac tape around it to hold it, then connect the duct hose to that. This explains the lack of heat coming out of my middle floor register. In addition, the two duct hoses that feed the middle and bedroom register have to travel over the top of the slide out support, and because of this they are crushed down to probably an inch or so of inside diameter, which, again, means very little heat coming out of them. I am going to install an air damper on the duct hose that feeds the register closest to the furnace, in hopes that by closing down to about 50% the other two registers will get better output. At least now I know the problem and I have a reasonable chance to fix it for a few bucks and some Eternabond tape to seal back up the opening I've made in the plastic underbelly to access all this. I can also report that there is NO specific heat duct that blows into the underbelly...the so-called "heated underbelly" simply means that heat lost through the un-insulated duct hose runs creates a very minor amount of heat down below, which is probably immediately lost through the cracks in the plastic underbelly where attached to the frame. There is ZERO insulation of any type down below. Hope this helps anyone trying to get better, more even heat out of their furnace in the Surveyor line, and specifically the 251RKS. MC
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Old 02-15-2019, 09:40 PM   #5
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Thank you for the information. I will have to check this out.
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Old 02-16-2019, 02:54 PM   #6
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Just a FWIW. On a trip early last year, crosswinds caused the front half of my underbelly to disengage, found the issue when we pulled into a campground.
So I took the entire underbelly off at that point.

On my trailer the "ducts" were skimpy mylar runs and were loosely installed. A bit of inner web searching led me to some info that said this kind of duct must be installed taught to get max air-flow. I've also read a number of posts from folks who had mice chew holes in the stuff.

So, while the underbelly was off, I replaced most of the ducting with rigid or heavy aluminum flex and aluminum taped all the joints. I'm now getting much better air flow to all registers.

If you search back on some of my posts, there are a couple of threads with several pictures of the work I did.
While I was at it, I neatened up the wire runs and covered the wires with split loom conduit.
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Old 02-16-2019, 05:59 PM   #7
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No, you don't do it that way.

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Originally Posted by frlancr View Post
pity the poor person who has to pull the furnace out for service, as you will destroy the duct hose connections
They never take the furnace out that way, so no problem. They take off the grille, then remove the front plenum cover, then the single anchor screw that holds the firebox/blower assembly in place. Then disconnect the gas line and four wires, and the firebox,blowers, and control board come out, leaving the entire plenum and duct assembly in place.

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Old 02-16-2019, 10:58 PM   #8
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My Rockwood has floor vents for the heat. I removed the factory installed vents and replaced them with vents that can be adjusted individually for air flow. The ability to adjust balances out the heat distribution. I have not noticed any additional strain on the furnace blower. I bought them at Lowe's.
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Old 02-17-2019, 10:17 AM   #9
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The Suburban installation manual...

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My Rockwood has floor vents for the heat. I removed the factory installed vents and replaced them with vents that can be adjusted individually for air flow. The ability to adjust balances out the heat distribution. I have not noticed any additional strain on the furnace blower. I bought them at Lowe's.
The Suburban installation manual warns against doing that. The risk is that once balancing begins and a few vents are restricted, the remaining room gets too hot. Then, instead of opening the other vents a tad, the user restricts the one remaining vent, too.

Then the furnace gets too hot and the high-limit switch cycles on and off, and the owner complains of cold air from the vents and irregular heating. If the furnace gets too hot regularly, the fire chamber can crack, leading to a dangerous situation.

The manual also has restrictions on the number of square inches of return air vent required. It is surely available on the Library on this website.

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Old 02-17-2019, 05:56 PM   #10
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The Suburban installation manual warns against doing that. The risk is that once balancing begins and a few vents are restricted, the remaining room gets too hot. Then, instead of opening the other vents a tad, the user restricts the one remaining vent, too.

Then the furnace gets too hot and the high-limit switch cycles on and off, and the owner complains of cold air from the vents and irregular heating. If the furnace gets too hot regularly, the fire chamber can crack, leading to a dangerous situation.

The manual also has restrictions on the number of square inches of return air vent required. It is surely available on the Library on this website.

Larry
I am not seeing that in the manual where it is referring to anything except the flow of air into and out of the burner itself, which indeed would be dangerous. There are no restrictions to the combustion chamber.
By changing the operation of the heated air vents does nothing to the airflow to the combustion chamber. The heat exchanger does not run any hotter than normal, the circulation fan pushes the air over a greater distance but that air flow is not restricted either. 5 cubic feet of air per second is 5 cubic feet of air per second whether it comes out of a vent 4 feet away from the fan or 12 feet away from the fan. If the total air movement volume at all of the vents added together is equal to the total air movement volume of the fan, what is the restriction?
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