Bathroom Heat - a more direct approach!

[Snackchaser]

Like others, we’ve been disappointed with the lack heating in the bathroom.  In our Oliver, even the kitchen had minimal air flow and hot air was blasting under the bed.  When I took a closer look at the duct routing from the furnace, the problems became obvious.  

There were two 4” ducts coming out of the furnace, one from the front outlet facing towards the registers, and the other from the rear outlet facing away from the registers.  The front outlet was connected to the bedroom register with one 90⁰ bend.  It had the shortest run with the least turns, and twice as much air flow as the other two combined.  The rear furnace outlet was connected to the kitchen register after making a 180⁰ u-turn.  From there it was Tee’d and reduced to 3” to feed the bathroom.  The 3” duct then takes a long and torturous path to reach the bathroom.  The resistance from over 280⁰ of turns, and the longer run, resulted in much lower air flow to both the kitchen and the bathroom.  I also found a hole from where the duct had been rubbing on the hot water valve, and the kitchen had a restrictively tight bend at the register.

Fortunately this was a relatively easy fix, and the results were significant.  Our 2022 Elite II has the Dometic furnace, but I suspect that other furnace brands could have similar ducting issues and it might be worth taking a look.

The sketch shows how the duct routing was modified for better balance to all three registers.  The bedroom and kitchen registers now feed from the high resistance u-turn at the rear furnace outlet.  The bathroom has its own feed from the front outlet giving it the minimal number of turns possible.

This modification involved moving the Tee which is under the kitchen cabinet.  There is an access port under the forward kitchen drawers to reach the Tee and kitchen register, and it’s best to pull them right out of the access port to work on them.  The 3” bathroom reducer stays in place and it gets a new duct directly to the front furnace outlet.  The bedroom/kitchen gets connected to the rear furnace outlet.  Rather than using flexible duct to make the 180⁰ u-turn, I used two 90⁰ rigid fittings for less flow resistance.

All of the parts needed for this modification are readily available at hardware stores.  They usually sell duct by the foot, I bought 5’.  Use sheet metal screws and foil duct tape for the connections to make sure they don't come apart.  The kitchen register can be screwed together from the inside of the register rather than trying to do it from under the cabinet.

I used an anemometer before and after the modification to measure flow, and a on-line calculator was used to get Cubic Feet per Minute (CFM):

                               Before   After

Bedroom - 4”       100.7      53.2

Kitchen - 4"          39.3         65

Bathroom - 3"     11.8         30.2

Total                     151.8       148.5

 

Cheers, Geoff

[mossemi]

Very nice mod with a simple approach and excellent results!  Thanks for sharing.

Mossey

[aaronorange]

Thanks, I have a new project. Betty was excited to hear your modification & solution 🙂

[Rivernerd]

On 2/3/2024 at 12:02 AM, Snackchaser said:

Our 2022 Elite II has the Dometic furnace, but I suspect that other furnace brands could have similar ducting issues and it might be worth taking a look.

Our 2022 Elite II has the Truma Varioheat furnace.  The Truma ducting is smaller, more substantial and, from what I can see in the photos, better installed.  

In addition to the mods detailed above, I recommend you consider adding a return air vent from the bath to the underside of the front dinette seat.   Our Truma Varioheat system came with that additional return air vent.  It really helps the flow of heated air.

[jd1923]

@Snackchaser were you able to get to or see the "reducer" on the way to the bathroom duct? I guess it just goes to smaller diameter ducting, so nothing you can do about it anyway.

[Mainiac]

It is "standard" operating procedure, in hot air ducting, to decrease duct size the further it gets from the heat source. The same amount of air in the 4" duct gets put into the 3" duct. This increases the velocity and helps move the heated air along. I just hope the is a direct path out of the bathroom and back to the return duct. Also hope that air is returned through the cabin and not through the basement. The return air is going to suck the air with the least resistance. Hopefully it is not the air from the drain 'scuppers'. That air might be 40°, or more,  cooler than cabin air, and the basement air might be 20° or more. The warmer the return air the more efficient the furnace is at heating. 

Edited May 1 by Mainiac
Correct type

[Snackchaser]

5 hours ago, jd1923 said:

@Snackchaser were you able to get to or see the "reducer" on the way to the bathroom duct? I guess it just goes to smaller diameter ducting, so nothing you can do about it anyway.

Yes, it's directly attached to the Tee for the kitchen register.   The 3" duct goes on to the bathroom through some sort of firewall and it's not easily reached.

There was enough slack in the 3" duct to pull the Tee (with attached reducer) out through the access port that's under the forward kitchen drawers.  The space is tight, and you will need to detach the 4" side from the furnace to get enough slack on that side.  You can make most of the new connections while it's out.

You'll need to disconnect the kitchen register first.  The screw holding the duct to the register can be reached through the access port, but it's easier to replace it from the inside of the register, rather than trying to do it blindly from inside the access port.

Cheers, Geoff

 Here's a photo that I forgot to add in the original post:

[aaronorange]

I'm in the middle of my conversion. I have removed the Kitchen/Bathroom T and attached the duct to the front of the furnace. I'm going to have a problem putting the T at the bedroom location due to waterlines in the way. (I'll include a photo) I didn't want a plumbing job. thinking of just going to the Kitchen and eliminating the sleeping area. Was your duct restricted like this?

 

[Rivernerd]

13 hours ago, aaronorange said:

Was your duct restricted like this?

Can you cut the duct, move the blue pex line(s) out of the way (pex lines are fairly flexible), and then reconnect the duct, incorporating the duct Tee?

[aaronorange]

 

Thanks, that's exactly what I did, the fix is now completed. Happy with the improved airflow. 

 

[jd1923]

On 4/28/2024 at 8:38 PM, aaronorange said:

thinking of just going to the Kitchen and eliminating the sleeping area. Was your duct restricted like this?

Like the simple design @Snackchaser showed. I will do our mod this summer. I’m also thinking of deleting the bed area duct. We’re camping in colder weather last few days and I have this one shut as much as possible which helps the air flow in the bath. The bed area duct is too close to the return and we like the cabin warm but cooler air where we sleep.

[jd1923]

Decided to submit another thread on my complete mod!

 

Edited June 25 by jd1923

[jd1923]

On 2/5/2024 at 9:29 AM, Rivernerd said:

In addition to the mods detailed above, I recommend you consider adding a return air vent from the bath to the underside of the front dinette seat. Our Truma Varioheat system came with that additional return air vent.  It really helps the flow of heated air.

I had to read this a couple time to realize yours was OEM installed. I'm trying to figure best location to drill. @Rivernerd could you take a picture from the bath side? 

I agree this is a necessary addition. Thank you!

Edited June 25 by jd1923

[SeaDawg]

Older thread, but relevant, I think.

 

[jd1923]

Finished up the bathroom vanity yesterday. I had a supply of 1/4" u-clips but the fiberglass is quite thick at the opening and decided that would be too much work, the placement must be extremely accurate. 

I merely used thin panhead wood screws with no taper. Measured with a digital caliper to drill just the right size holes. Added a SS washer so the screw head would not drag on the plastic. Thoroughly cleaned off all the old caulk and sealant. This product has just the right size opening and adequate length: uxcell U Channel Edge Trim, 6.5ft Length Rubber Guard Seal Strip Edge Protector Fit for 1.5-2.5mm Edge, (13/64" W x 5/16" H) White - Amazon.com

To-dos left are the bathroom to under dinette vent and the return air filter housing. Waiting for parts...

[jd1923]

On 6/15/2024 at 7:18 PM, SeaDawg said:

Older thread, but relevant, I think.

Thanks again Sherry. Just found the picture I was asking for in the link you supplied. (It appears @Rivernerd has been offline for a week.)

The vent is behind the toilet where you could actually fit a standard drill vs. a 90-angle drill. It does look like a 3" vent in the pic vs. the 4" installed elsewhere. I would not add another vent from under the dinette to the hallway, since the idea is to create air return from the far bathroom vent through the basement and around the rear back to the furnace. This could actually assist in pulling more air out of the bathroom duct too.

Now I merely have to get up the nerve to pick a spot and start drilling! Will start with an 1/8" hole so I can adjust location of the full vent hole as needed. Just noted in the other thread that OTT installed a 2" vent in this location.

Edited June 17 by jd1923
Added last sentence

[jd1923]

See this post for a complete installation, my simple mod: Furnace Duct Modification for Improved Air Flow and Circulation - Ollie Modifications - Oliver Owner Forums (olivertraveltrailers.com)