Replacing Furnace Ducts

Dustdevil · 01-21-2017, 09:52 PM

So, the last time out, we ran the furnace in the 2006 Seneca 34SS. Worked fine, but the inside of the cabinets seemed awful hot. I had a hunch that the furnace ducts might be torn in a place or two. Plus, I wanted to go find the subwoofer for the surround sound system anyway, so I started to take apart the bulkheads in the kitchen cabinets. Turns out, the ducting DID have multiple tears, and needed replacing. I got one done, but the second snakes its way to the underbelly, and I am having real trouble getting to a place where I can even see it, much less replace it. It's in horrible shape near the furnace, but the ducts up above and behind the outside sanitary cabinet seem in unusually good shape. I think I'll get it figured out. But I have one question:

Is there supposed to be a small diameter (2" or 2-1/2") duct that supplies hot air directly to the interior of the cabinets to keep pipes under the stove, oven, and sink warm enough to avoid freezing? One of these small ducts is only about 24" long, and it just empties to the cabinet interior, with no apparent place to connect it. The ducts handling actual heating air to the normal floor and cabinet outlets are all 4" diameter. Is this normal, or is it something I should be looking for some alternative outlet?

abarkl · 01-21-2017, 10:14 PM

With a few pictures as reference we would be happy to compare it to ours if it will help.

Grumpy · 01-22-2017, 07:14 AM

That 2" is probably supposed to blow into the belly to keep the tank area warm. Look for a hole in the floor where it should go into.

Dustdevil · 01-22-2017, 01:41 PM

OK, so here are two pictures of the under-cabinet area. The smaller duct in front is the one that empties right up against the subwoofer. It simply dumps hot air into the cabinet. This seems odd, as I believe the radiant heat that escapes the duct is plenty to keep the under-cabinet area warm. We also camp in freezing temps very rarely, and the ducts run right alongside the under-cabinet piping most of the way. All available ducts seem to blow hot air, so I am relatively certain this duct is superfluous. I'd be inclined to cap it off.

You may be able to see that the larger of the ducts is in pretty sad shape. This is the duct which supplies the back bedroom floor vent as well as the small vent under the bathroom sink. The only other vent to the rear of the furnace is the water closet floor vent, which is supplied by the other large duct shown exiting toward the right side of the picture. That one is in much better shape, and likely does not need replacing. Once the ducts exit the belly right around the outside sanitary bay, the ducts also seem like they are nearly new. It's just the 4" duct exiting the plenum to the left of the small duct that's in really bad shape.

So, I'm just wondering if anyone knows for a fact that that small duct is supposed to exit inside the cabinets to keep them warm. It actually seems to make the under-cabinet area way too hot.

oldmanAZ · 01-22-2017, 02:08 PM

IMO, it seems unlikely the duct is to heat the cabinet area. The heat loss from the ducts could keep that area warm.

You didn't install the subwoofer, did you? Did you look under and behind subwoofer to see if maybe the duct had been pulled out and left out? A previous owner that installed the subwoofer might not have worried about heating and ducting.

Nukeneck · 01-22-2017, 02:22 PM

"You didn't install the subwoofer, did you? Did you look under and behind subwoofer to see if maybe the duct had been pulled out and left out? A previous owner that installed the subwoofer might not have worried about heating and ducting."

That's a good point. I'd check that first. Another option to capping off the 2 1/2" is to add a register to your cabinet panel, connect the ducting and have it blow to your living area if you need the warmth.

abarkl · 01-22-2017, 02:30 PM

As you know we don't own the 34SS but the 35GS. Ours is different in many ways, starting with ours is all on the road side.
We have been all through ours last year to patch small holes and seal areas the factory did not.

Our guess is that the small duct was plumbed to be connected to some type of vent that exited in the kitchen area perhaps similar to the vanity vent configuration, but the actual vent was not installed (overlooked).

In our previous motorhomes of another brand there were holes in the flooring beneath the carpet to allow coach heat to pass through to the tanks, plumbing, and wet bay cabinet.

Perhaps if you don't find a convenient method of replacing the ducting there is more of a plastic piping that could be inserted into it as a replacement.

P.S. Our subwoofer is also under the kitchen sink.

Dustdevil · 01-22-2017, 02:45 PM

Quote:

Originally Posted by oldmanAZ

IMO, it seems unlikely the duct is to heat the cabinet area. The heat loss from the ducts could keep that area warm.

You didn't install the subwoofer, did you? Did you look under and behind subwoofer to see if maybe the duct had been pulled out and left out? A previous owner that installed the subwoofer might not have worried about heating and ducting.

Good point, and no, I didn't install the subwoofer. Nor did I look underneath to see if there is an additional opening. Even as small as that duct is, it won't even come close to fitting through the existing opening. That opening has two 4" and one 2-1/2" already leading through.

It's raining cats and dogs right now, through tomorrow afternoon. When it dries out a bit, I'll get the street side wheel skirt off of the body, and get a look inside the belly (assuming that actually gives me a view). That might give me a bit more insight as to where each of these ducts go. For the life of me, I can't tell how two 4" and one 2-1/2" feed three ducts, when one of them is a branch off the larger 4". I'll post back here on what I find.

Grumpy · 01-22-2017, 03:35 PM

Sub-woofer looks like the factory install we had in our 08, including plastic strap.

Dustdevil · 01-22-2017, 05:50 PM

Well, I pulled the subwoofer loose, cleaned all the dust from around there. Nothing under the subwoofer, so I have no idea what might have been the use of that small duct. So, I capped it off temporarily so the cabinets don't get so hot. Found my fifth outlet, which is only visible when the main living room slide is open. They all blow hot air now, after I patched a few holes in the bad ducting. Until I figure out how to fish a replacement duct through the openings and through the underbelly, this will have to do. I believe the wheel skirts have to come off for that, but who knows?

The subwoofer and all the other speakers work, but the DVD player/amplifier is not so hot. Works, but not such great sound. I'll replace that before long.

abarkl · 01-22-2017, 06:07 PM

The Executive 1000 sound system they used at that time in the Senecas has a lot to be desired.
We have had to replace one of the satellite speakers to eliminate a crackling noise, and remounted the subwoofer to minimize it from contacting surrounding cabinetry and creating unwanted sounds, but it's "muddy" at best.

We haven't replaced ours but another owner was working on that project awhile back;
http://www.jaycoowners.com/forums/gr...ombo+unit.html

In all our motorhomes we have replaced all the tube TVs with flat panel and added sound bars to each. The sound bars support additional input types besides the TV optical such as Bluetooth.
As we have in our stationary home similar sound bars but they also have Bluetooth connected subwoofers very similar looking and in size to the Executive 1000 in the RV. However these do require an AC connected amplifier for each piece, hence much better sound.

Dustdevil · 01-23-2017, 09:44 AM

Quote:

Originally Posted by abarkl

The Executive 1000 sound system they used at that time in the Senecas has a lot to be desired.
We have had to replace one of the satellite speakers to eliminate a crackling noise, and remounted the subwoofer to minimize it from contacting surrounding cabinetry and creating unwanted sounds, but it's "muddy" at best.

We haven't replaced ours but another owner was working on that project awhile back;
http://www.jaycoowners.com/forums/gr...ombo+unit.html

In all our motorhomes we have replaced all the tube TVs with flat panel and added sound bars to each. The sound bars support additional input types besides the TV optical such as Bluetooth.
As we have in our stationary home similar sound bars but they also have Bluetooth connected subwoofers very similar looking and in size to the Executive 1000 in the RV. However these do require an AC connected amplifier for each piece, hence much better sound.

Before I'm done, I'll replace this also.

Dustdevil · 01-23-2017, 08:50 PM

OK. So, I got a spare hour early this evening, and followed up a hunch. I pulled out the wheel skirt, removed the mud flaps front and rear of the wheels. Removed the screws and pulled down the wheel well sheet metal as far as I could without bending and destroying it. All the ducts are visible, if not reachable. I see that the worst of them is actually very nice in the underbelly, and is actually an extension of another duct in very good shape. So, the part above the floor is the only part that is bad. I can separate the two at the metal connector, and replace the portion that is not in good shape, and the ducts will be overall very good from that point forward. This is do-able, and with maybe a full day invested, it will all be buttoned up and re-sealed to be water-tight once again. A little expanding foam and a little silicone sealant, and good as new! I'll post some pictures when I'm done. Probably this weekend.

abarkl · 01-23-2017, 09:04 PM

We are glad to hear your results and look forward to more pictures for reference.
Thanks.

Goflight2 · 01-26-2017, 09:09 PM

I am picking up my 2007 34SS tomorrow. When I tested the heater, I found that the bedroom floor duct and the bathroom duct did not blow much air at all. The dealer said they checked the ducting today and everything was in working condition with no rips, tears, etc.
does this sound normal? Other vents are blowing hot air fine. If you cover them with tape, the rear blows fine. They suggested I put in vents with registers in them so I could direct heat better. Thoughts?

Dustdevil · 01-26-2017, 11:58 PM

All normal. Pressure drops as you move away from the furnace and this is natural. I wouldn't even bother with registers. You could get some pretty big temp variations from one zone to another, and the standard system actually works pretty well. Time may be better spent elsewhere.

Dustdevil · 01-27-2017, 08:34 PM

OK. So, I finished replacing all the ducts showing deterioration. Turns out, when you pull down the galvanized steel box surround for the wheel well, the ducts are all right there. And the one I really needed to replace, and dreaded the most, was actually spliced right in the middle, because it's so long. I unwrapped the splice, pulled the new duct through the floor and into the underbelly, reconnected both ends, and swapped the small diameter ducts and their entry points into the furnace air box. Somewhere along the line, someone got them mixed up, and all it took was a swap. Aimed the shorty straight down the hole in the floor to heat up the underbelly (which I believe is the way it's intended), and all is well. Works great! Blowing hot air through all ducts, although the one farthest away in the bedroom is not blowing very hard, as expected. It does spew plenty of heat. It's not as though we use the furnace at night very much. Both of us would much rather sleep in a chilly RV with plenty of blankets, then turn on the furnace first thing in the morning. On those really cold nights in an RV park, I'll have an electric heater. For really cold nights while boondocking, we'll just set the thermostat for maybe 50 or 55F and call it a night.

I'll post some pictures later this weekend.

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