Relocate the furnace inlet grill and block off that opening?

[John E Davies]

14 minutes ago, Overland said:

Either way, the dinette is certainly an easier solution,

Thanks for the pics, I will definitely put those extra holes on the far side of the hallway.

John Davies

Spokane WA

 

Edited February 21, 2021 by John E Davies

[Overland]

You’ll run into a similar airflow problem on the other side, since the black tank drain takes up the majority of the channel underneath the dinette floor. You could remove the drain, of course, since you’ve got a composting toilet. Otherwise, the airflow will be limited to the gap between the floor and hull/tanks.

Perhaps a vent under the pantry?  Plenty of airflow between there and the furnace. 

[John E Davies]

I am not sure how much space is at the floor directly under the closet and entry way, but there is plenty of room for airflow right in front of the grey tank.  Regardless, I have already added a 4 inch round hole in the rear dinette wall and in the streetside bed wall, so combined they should be plenty adequate if I put a similar one in that space.

BTW, does an Ollie inspector still put little smily faces on all the waste water connections, or was I just lucky?

John Davies

Spokane WA

Edited February 21, 2021 by John E Davies

[Jim_Oker]

On 2/15/2021 at 3:10 PM, DavePhelps said:

The main issue that has come up regarding this is that the blower could potentially receive less air due to passage restriction and/or have to work harder to get the air, causing overheating and furnace shut down. This is what Jason brought up when I posed him the question, but he wasn't sure. He said he would bring it up during the next design meeting. I don't really see this being an issue as there is lots of free space down below for air to move, just no space for duct work.

I'm wondering how reasonably testable this question is. I.e. perhaps  by measuring amps going to the furnace while it's operating? If this draw is reasonably constant then one could mock up a mod by temporarily blocking the  existing return and opening a temporary one at one of the dinette access hatches for instance and then  compare amp draw. If there's  no discernable difference I would  venture a guess  that this  is a good signal that the blower is  not working harder. I imagine that there are techniques for measuring air flow through the hot air vents or ducting as well but that likely involves more specialized HVAC tools versus a vanilla multimeter... perhaps with a Rube Goldberg setup with a Facetiming phone or some such strapped in there as well?)

Edited February 23, 2021 by Jim_Oker

[AndrewK]

Not scientific but, I have covered the return air vent and did not find any significant change In the volume of air or sound coming from the furnace nor did the sound of the fan change.   

My wife sleeps above the furnace and could not hear any difference in the sound volume or characteristics, while lying on the bed.

Andrew
 

 

Edited February 23, 2021 by AndrewK

[Jim_Oker]

1 hour ago, AndrewK said:

I have covered the return air vent and did not find any significant change In the volume of air or sound coming from the furnace nor did the sound of the fan change.

Did you create another opening for air return from the cabin into the basement?

[John E Davies]

1 hour ago, AndrewK said:

Not scientific but, I have covered the return air vent and did not find any significant change In the volume of air or sound coming from the furnace nor did the sound of the fan change.   

My wife sleeps above the furnace and could not hear any difference in the sound volume or characteristics, while lying on the bed.

That is good to know, thanks, what did you cover the grill cutout with? Cardboard? I was thinking that a 5/16” piece of HDPE plastic, with sound insulation inside it, cut to fit the hole shape, plus insulation in the rest of that vertical inside wall, would significantly lower the sound level. I would also add rubber seals around the outside to stop any leakage. Just covering the hole isn’t enough, it needs some acoustic sound baffling, like that stereo mat stuff you glue inside your car doors. But it needs to be able to stop high frequency sound, not those deep low frequency vibrations.

John Davies

Spokane WA

Edited February 23, 2021 by John E Davies

[AndrewK]

Jim/John,

I was camping in Zion when I read John’s original post on the subject and thought what a good idea to reduce the furnace’s sound level.  The furnace was on (27 degrees out!) and I grabbed my pillow and just covered the intake.  

To my suprise, there was little/no appreciable change in the sound level, air volume output or the sound from the fan, suggesting no load change.

Andrew

[John E Davies]

On 2/23/2021 at 2:45 PM, AndrewK said:

Jim/John,

I was camping in Zion when I read John’s original post on the subject and thought what a good idea to reduce the furnace’s sound level.  The furnace was on (27 degrees out!) and I grabbed my pillow and just covered the intake.  

To my suprise, there was little/no appreciable change in the sound level, air volume output or the sound from the fan, suggesting no load change.

Andrew

You should have used something more dense 😬, I tried that today, I used two pieces of Coleman 1/2” eggcrate foam sleeping bag pad. I jammed them hard onto the intake opening (with the grill removed) and the sound definitely became deeper and more muffled. I launched my sound measuring app ..... https://apps.apple.com/us/app/decibel-meter-sound-detector/id1254994873.... and took some readings with the iPhone sitting on top of the curb side mattress, near the edge. With the grill open it was about 58 dBa. With it covered it was 52 dBa. That is a significant improvement! And that doesn’t include any inside sound insulating tiles or a tight fitting rubber gasket around a cover.... I think you might get close to a 10 dBa reduction, which is huge (half as loud). I had the front dinette cushion and hatch lifted and did not note any signs of straining from the fan motor.

I found the specs on the return air for MY furnace (Suburban NT20SQ), they require 55 square inches located immediately in front of the unit. Oliver cut a 5”x10.5” hole. I know why they did that, but the furnace instructions are written for the typical stick and staple installation, where there is no huge volume of free air between hull sections to take advantage of...

I did some more looking and thinking, and decided to leave the thing alone for now. If I replace the fridge with a DC compressor one I will consider adding the return opening there by the front door, with a custom insulated duct going down into the floor. I decided against cutting a big hole under the front dinette seat because I would lose too much valuable storage volume.

John Davies

Spokane WA

 

[ScubaRx]

I would not let them cut the furnace return in Hull #050. Robert Partee (service manager, the only salesman, my friend, the MAN) argued with me about it every time I was at the factory during our build in 2013. I won. The furnace has run fine and heated very well for these past seven plus years.  I had it on just the other night during the recent wave of ice and snow when it was in the low teens here in the Deep South.

I did have them install three of the lower access doors. At the time, it was just something I dreamed up during one of my build visits. I thought they would look cool and I suggested using the same hatch that was to be used in the bathroom (only reversed so it would open down instead of up.) In retrospect, they've come in handy for us to access the basement and the valves under the curbside bed (we have the raised beds) the one under the street side bed was really just for symmetry and looks, but it does allow me to easily reach the reset button on the inverter if I need to. Apparently the folks that saw ours started asking for them and now they are options?

If I need to introduce more air flow into the basement I just open one or more of those doors. They would serve nicely as the furnace return also, although we don't open them for that as it doesn't seem necessary. I've always been able to keep the basement areas within 10-15 degrees of cabin temperature with no great amount of effort.

I've never noticed the furnace to be noisy, except the time the fan got into the shroud and I had to pull the furnace and tighten up everything. Ours has to come out through the inside and it's sort of a PITA.

Edited March 1, 2021 by ScubaRx

[Mainiac]

By adding the butterfly vent, high in bathroom wall, we have had the bathroom heat a lot better. The door doesn't have to be open. The air circulates a lot easier and hence relieves pressure on the fan. Would think restricting any airflow into the furnace return air vent might raise the noise as the fan works harder. Also by restricting heated air from the cabin, it would have to bring in unheated outside air through the drain/vents. By shutting slightly the heat vent near the return it forces the heated air further through the system.

[Rivernerd]

On 2/12/2021 at 2:47 PM, SeaDawg said:

I guess the elephant in the room is--what does the furnace grate actually do, in a ducted furnace? 

I am not an engineer, and I am joining this thread many months later.  But, I do know that in a house, the purpose of a "furnace grate" is to provide a return air path to the furnace to balance the HVAC system.

We owned a large L-shaped, 2-story  home in the Seattle area that had only one cold air return per floor, located near the joint in the "L".  We heated with forced air gas.  The rooms at the ends of the legs of the "L" were always cold in the winter, while the rooms in the center of the "L" were warm.  I was advised this is because there were not return air vents in those outward rooms, and so the flow of heated air was not balanced.  It was too expensive to retrofit, so we just lived with it.

When we built our new home in Idaho, we ensured that the HVAC contractor placed return air vents in every room, on the opposite side of the room from the supply air vent, not just one or two big "furnace grates" in the middle of the structure.  We also heat the Idaho home with forced air gas.  Even though winters are much colder in the Idaho mountains than in the Seattle area, the outward rooms in the Idaho home stay at about the same temp as the core of the house.

So, I expect the purpose of the return air vent under the rear dinette/bed area in an Elite II is to balance the system, i.e., to pull cooled air back to the furnace for reheating and redistribution through the supply ducts into the cabin.  If I understand correctly, the return air grill on an Elite II is cut into the inner hull under the curb side bed.  This places it just inboard of the furnace in an Elite II, and at least a few feet from the supply air vents.  This allows the system to achieve "balance," or more even heating within the cabin.

Since the trailer cabin is essentially one "room," it does not surprise me that there is only one return air grill.  But, it also does not surprise me that the bathroom, which is the only "room" in the trailer separated from the cabin by a door, would be colder than the rest of the cabin without its own return air ducting.  Thus, it makes sense that Mainiac's addition of a butterfly vent high in the bathroom wall resulted in a warmer bathroom.  It appears to me that this design allows the space between the inner and outer hulls to act as a return air "duct" for the bath, balancing the flow of heated air into that small, but separate, room.

We don't take delivery on our Elite II until next summer.  But if we find that the bathroom feels cold when camping in cooler temps, I plan to add a butterfly vent, like Mainiac did.  Thanks, Mainiac!

[SeaDawg]

@Rivernerd 

Yes, I understand the need for return vents, or jumper ducts, transom vents, undercutting doors, etc. in home hvac.

We also built separate returns in each room in our new home 6 years ago. It made for a lot of extra ducting, and a big challenge for our hvac installer, but smoke and pressure tests showed that he did an amazing job, and it works very well.

Balancing pressures and return air in a small trailer is another different,  and interesting conundrum. 

If you haven't seen it, here's another link to @Mainiac's excellent mod, which suited his needs very well. It's another good discussion. 

In our older Elites,  there is no duct to the bath. Central furnace, no ducting. We heat the bath by propping the bath door open.

I'm certainly no hvac expert, but I'm thinking the original location for the vent , with a ducted furnace, at/near the furnace location, is probably the most efficient,  though perhaps not the most quiet? 

 

[Mike and Carol]

We’ve found that the duct in the bath doesn’t do much.  In cold weather we just keep the bath door open all the time when we’re not in there doing something.

[CnC]

Coming late to this thread, I'll add two things.

I have concern about our 2020 LE2's first vent being too close to the return air grille - in the world of HVAC this is called short-cycling.  I plan to reduce the flow at that air vent, which will lessen the short-cycling and provide better air flow to the bathroom.

Second, in the world of ventilation there is one rule that is supreme - what comes in must go out and what goes out must come in - otherwise there is no transfer of air.

I liked the baffled vent in the bathroom idea 👍

[Fritz]

3 hours ago, CnC said:

I have concern about our 2020 LE2's first vent being too close to the return air grille - in the world of HVAC this is called short-cycling.  I plan to reduce the flow at that air vent, which will lessen the short-cycling and provide better air flow to the bathroom.

I spoke with Jason Essary about this when we picked up the trailer.   He expressed concern that reducing the warm-air vent closest to the cold-air return would force more air into the second duct (the one that sends warm air to the vent under the drawers and the one in the bathroom, but that this line wouldn't carry enough air for the the furnace to operate correctly if the closest air vent were closed too much.  So I suppose it would depend on just how much you close off the closest air vent.

I agree that the system short-cycles.  However, the interior space is sufficiently small that the air mixes well enough.  It gets warm throughout the cabin, in our experience.  Leaving the bathroom door slightly open (or installing a vent) helps.

[CnC]

Makes sense.  I was thinking 50%.  Thanks, Fritz.

[GAP]

On 3/1/2021 at 7:43 AM, Mainiac said:

By adding the butterfly vent, high in bathroom wall, we have had the bathroom heat a lot better. The door doesn't have to be open. The air circulates a lot easier and hence relieves pressure on the fan. Would think restricting any airflow into the furnace return air vent might raise the noise as the fan works harder. Also by restricting heated air from the cabin, it would have to bring in unheated outside air through the drain/vents. By shutting slightly the heat vent near the return it forces the heated air further through the system.

Hey Maniac,

As the area you vented is double walled, where did you get the vent?  Is it finished on the inside of the bathroom as well?

[GAP]

On 11/18/2021 at 3:52 PM, Fritz said:

I spoke with Jason Essary about this when we picked up the trailer.   He expressed concern that reducing the warm-air vent closest to the cold-air return would force more air into the second duct (the one that sends warm air to the vent under the drawers and the one in the bathroom, but that this line wouldn't carry enough air for the the furnace to operate correctly if the closest air vent were closed too much.  So I suppose it would depend on just how much you close off the closest air vent.

I agree that the system short-cycles.  However, the interior space is sufficiently small that the air mixes well enough.  It gets warm throughout the cabin, in our experience.  Leaving the bathroom door slightly open (or installing a vent) helps.

I was considering trying to cap the closest vent (to the heater intake) altogether and, in it's place, running a line under the floor to the street side and, if possible, as far forward as the rear dinette seat.  Adding a round vent there.  This would bring heat past the outside shower, and under the battery compartment, both areas that can use a little love.  Venting the bathroom wall and perhaps doing as John suggested with allowing some flow through the closet all seems like it should help minimize the most vulnerable area.  Thoughts?

[Mainiac]

38 minutes ago, GAP said:

Hey Maniac,

As the area you vented is double walled, where did you get the vent?  Is it finished on the inside of the bathroom as well?

We put a matching SS vent on the inside. You see screw heads outside, double nuts inside. 

[GAP]

On 11/18/2021 at 3:52 PM, Fritz said:

He expressed concern that reducing the warm-air vent closest to the cold-air return would force more air into the second duct (the one that sends warm air to the vent under the drawers and the one in the bathroom, but that this line wouldn't carry enough air for the the furnace to operate correctly if the closest air vent were closed too much.  So I suppose it would depend on just how much you close off the closest air vent.

 

I'm wondering if the addition of a vent through the bathroom wall would negate the potential of this problem.  It would allow air to flow more easily through to the bathroom (which had been a dead end), which would, in turn rebalance the air flowing into and out of the furnace.  As I pondered above, repositioning the hose and exhaust that is closest to the cold-air return to a round vent under the rear dinette seat.  Should help with keeping the balance as well, with the added benefit of sharing some heat with  some vulnerable spots such as the battery compartment and exterior shower.  I took a quick look and it seems like running the vent hose, under the floor to the street side, under the inverter, past the battery box and into the compartment under the seat would be fairly easy.

 

[Fritz]

1 hour ago, GAP said:

I'm wondering if the addition of a vent through the bathroom wall would negate the potential of this problem. 

The question that I have -- and I like your idea -- is whether this configuration of return air vent (with associated length, twists, and turns) would have too great of a friction loss given the size of hose that would fit, thereby making the heater work inefficiently (or perhaps shorter life because of getting too hot).  You might want to look up specs on the furnace to see what the friction-loss constraints would be for this return-air venting location and configuration.  Please let us know if you do this -- I think several of us would be interested.

[GAP]

14 hours ago, Fritz said:

The question that I have -- and I like your idea -- is whether this configuration of return air vent (with associated length, twists, and turns) would have too great of a friction loss given the size of hose that would fit, thereby making the heater work inefficiently (or perhaps shorter life because of getting too hot).  You might want to look up specs on the furnace to see what the friction-loss constraints would be for this return-air venting location and configuration.  Please let us know if you do this -- I think several of us would be interested.

I think you are talking a bit above my pay grade.  My plan was to brail my way through this project.  I'd give the furnace a good listen, perhaps deploying John's suggested sound level app.  after running the hose to the rear dinette seat and putting a vent in the bathroom, would run the furnace again testing with app and listening for similar sound output.  If no additional volume or strain, job's done.  If otherwise, my loose plan B is to tap back into the now unused, original  4" vent that is by the return air grate and incrementally open the blades to restore balance.  BTW, I assume that Oliver supplying a bladed vent under the sink means that the system can withstand minor changes in pressure.  For Plan B, I'd swap this bladed cover to the rear vent.  Will report back on progress.

[Mainiac]

When everyone Is thinking about how the furnace is getting it's intake air, keep this in  mind. There are built in drains in the outer hull. If you block off the furnace cold air return in any way I am sure some that some air will come In those holes. And in some circumstances that air could be quite 'chilly'. Don't think I have ever counted them, but they are visible from underneath hidden by SS caps. At one time the thought had crossed my mind that the whole space around the inner hull could be pressurized by conditioned air, but the emergency drains would be compromised. Then thoughts about elimination of the present AC, and maybe a heat pump came to mind. However, for the present, we are more than pleased how the system now seems more balanced with the high wall vent. It functions very well, and we can keep that door closed...

[rich.dev]

On 2/15/2021 at 6:10 PM, DavePhelps said:

I'll post back in a few weeks when I get my test all completed.

I know it's been a while, did you complete your tests, if yes what where the results?