2022 Alpine 3790FK low furnace air flow to kitchen and bedroom/bathroom

[Cldicaprio]

Here we are again with yet another issue in our new Alpine. Turned the furnace on for the first time this morning and while there was plenty of hot air coming out of the floor vent in the living room, there was virtually none coming out of the vent in the front kitchen, and barely any out of the bedroom and bathroom vents in the back. Also, there was warm air blowing OUT of the cold air return?! That can’t be right? If we need to look at all the venting underneath do we do that by removing basement wall panels? or is there a bigger problem here with warm air blowing out of the cold air return?

[bsmith0404]

Not sure how you’re getting warm air out of the cold air returns since the two ducts are completely separate. Unless you have it set to heat pump or auto instead of furnace. First thing is to verify your heat settings. The heat pump is in the AC unit and will give you heat from the ceiling ducts, furnace is in the floor. Not sure how the ducting is set up on the 3790, but I’m assuming they use the round dryer type hoses from the furnace into the ducts for the different levels. Could be those aren’t connected properly.

[chuckster57]

If you can remove the grill and the furnace is behind it you might find some ducting has come loose from the furnace. The lines are typically twisted on with an alignment tab, and I have often times seen them not secured right, letting them fall off. May look like this:

https://images.search.yahoo.com/imag...ne&fr2=piv-web

Just insert the long tabs, line up the indexing tab with the slot on the furnace and twist.

[rhagfo]

RV ducting leaks like sieve. Get a roll of metal duct tape and do some sealing. Also floor registers with dampers help even the air flow.

[Cldicaprio]

found the problem- SMH. thank you all for the replies!

[chuckster57]

I would use some aluminum tape after tightening the clamp.

[Cldicaprio]

Originally Posted by chuckster57

I would use some aluminum tape after tightening the clamp.

We did thank you. Unfortunately only fixed part of the problem. ugh. kitchen getting good flow and heat now along with the living room. But still barely a breeze in the bedroom and bathroom. Must be disconnected on down the line too.

[Cldicaprio]

Originally Posted by chuckster57

If you can remove the grill and the furnace is behind it you might find some ducting has come loose from the furnace. The lines are typically twisted on with an alignment tab, and I have often times seen them not secured right, letting them fall off. May look like this:

https://images.search.yahoo.com/imag...ne&fr2=piv-web

Just insert the long tabs, line up the indexing tab with the slot on the furnace and twist.

that’s exactly what happened. we reconnected and clamped it, used some aluminum tape as well. But still barely any air flow to the back in the bedroom and bathroom. Assuming it’s disconnected on down the line somewhere else too- will have to continue the hunt …ridiculous on a brand new rig!!!

[Cldicaprio]

Originally Posted by bsmith0404

Not sure how you’re getting warm air out of the cold air returns since the two ducts are completely separate. Unless you have it set to heat pump or auto instead of furnace. First thing is to verify your heat settings. The heat pump is in the AC unit and will give you heat from the ceiling ducts, furnace is in the floor. Not sure how the ducting is set up on the 3790, but I’m assuming they use the round dryer type hoses from the furnace into the ducts for the different levels. Could be those aren’t connected properly.

venting wasn’t connected so the heat was blowing in that compartment and coming out the cold air return. reconnected it and have good air flow in living room and front kitchen now, but still barely a breeze coming out of the back bedroom and bathroom. Assume it’s disconnected somewhere down the line in another place too. so the hunt continues. I know you hear about it all the time, but This kind of crap should not happen on a brand new rig!! Some days i wish we’d have kept our 2004 Cardinal. Thing was built like a brick sh&@! house with zero issues. And the minor ones that creeped up were simple fixes.

[NH_Bulldog]

Is that all you have for ducts connected to the furnace? My comparatively small camper has three 4” ducts connected to the furnace plenum, plus one 2” duct for the underbelly space.

Anyway, I would pull the heat registers and check the connections. It is possible that the duct is compromised somewhere along the way, but the corrugated “dryer” duct also naturally restricts air volume the longer the distance the air has to travel. My furnace is at the midpoint of the trailer so we have equal flow at all 3 registers

[Cldicaprio]

Originally Posted by NH_Bulldog

Is that all you have for ducts connected to the furnace? My comparatively small camper has three 4” ducts connected to the furnace plenum, plus one 2” duct for the underbelly space.

Anyway, I would pull the heat registers and check the connections. It is possible that the duct is compromised somewhere along the way, but the corrugated “dryer” duct also naturally restricts air volume the longer the distance the air has to travel. My furnace is at the midpoint of the trailer so we have equal flow at all 3 registers

If you look at the picture i posted you can see that there’s one 4” duct, one 2” for the underbelly, and one that isn’t punched out— now i’m wondering if that’s where the back venting is supposed to be connected and it’s never even been connected?? wouldn’t surprise me a bit. wish i knew someone else who had 3790fk who could look at theirs for me!

[chuckster57]

An inspection mirror would allow you to see the other side without much trouble.

[Cldicaprio]

Originally Posted by chuckster57

An inspection mirror would allow you to see the other side without much trouble.

good idea!

[travelin texans]

Originally Posted by Cldicaprio

If you look at the picture i posted you can see that there’s one 4” duct, one 2” for the underbelly, and one that isn’t punched out— now i’m wondering if that’s where the back venting is supposed to be connected and it’s never even been connected?? wouldn’t surprise me a bit. wish i knew someone else who had 3790fk who could look at theirs for me!

There's most likely more ducts on the opposite side of the plenum. I don't think there's a dedicated return duct, there's most likely a gap under a cabinet or 2, &/or the steps if a 5th wheel, near the furnace that pulls from the interior as a return.

[RickV]

I have the 2021 3790FK and while mine has OK flow from the one in front of the recliner and the one under the bar (which is a stupid place for it) I get very little from the two in the bedroom/bathroom. I brought this up while it was still under warranty and the dealer said "It is working and the low flow is normal". Last year we had reservations at Lowry Campground near Dillon, Co. in late May. This campground only has 30amp electric so I knew we'd need to be able to run the gas furnace with forecast lows in the lower 30's and I wanted to try it out before we got there. So I navigate to turn on the furnace and there's no option for gas only electric. We were heading up to Lowry Campground in about a week, so after I make a few calls I got hooked up to an ASI Tech he sent me an updated In-Command plan file to upload which added the gas furnace option.
How did you get to the Furnace? If your floor plan is the same as mine did you remove the two recliners to get to the return?

[Cldicaprio]

Originally Posted by RickV

I have the 2021 3790FK and while mine has OK flow from the one in front of the recliner and the one under the bar (which is a stupid place for it) I get very little from the two in the bedroom/bathroom. I brought this up while it was still under warranty and the dealer said "It is working and the low flow is normal". Last year we had reservations at Lowry Campground near Dillon, Co. in late May. This campground only has 30amp electric so I knew we'd need to be able to run the gas furnace with forecast lows in the lower 30's and I wanted to try it out before we got there. So I navigate to turn on the furnace and there's no option for gas only electric. We were heading up to Lowry Campground in about a week, so after I make a few calls I got hooked up to an ASI Tech he sent me an updated In-Command plan file to upload which added the gas furnace option.
How did you get to the Furnace? If your floor plan is the same as mine did you remove the two recliners to get to the return?

Totally agree that under the bar is a stupid place for the vent!!! i LOVE this floor plan but having been full
time on and off for years and again in this one- we find ourselves saying that more often than i’d like!!
The command center did have the gas option - but we had to google it because it’s not listed for the front AC, you’ll find it in the rear ac controls when you set it to heat. The front AC cannot be set to heat.
As for what the technician said about low flow being “normal”, that’s ridiculous. For what they advertise as a full time four season coach, how are you not supposed to freeze to death in the bathroom
or bedroom without any heat coming out of the vent??! We’ve had 15-20 year old 5ers built better than this.
We have not yet gotten back under the coach to look for more disconnected venting, will update when we do what we find.

[Cldicaprio]

also- the cold air return ios not really a return i guess, but is under the front the stairs which have grates for cold air return, not behind the recliner. the furnace itself
is in the compartment on the side with the command control box. We had to take out a wall
panel in the compartment to get to it.

[Cldicaprio]

Originally Posted by travelin texans

There's most likely more ducts on the opposite side of the plenum. I don't think there's a dedicated return duct, there's most likely a gap under a cabinet or 2, &/or the steps if a 5th wheel, near the furnace that pulls from the interior as a return.

You’re probably right about the cold air return, i just call it that because that’s what it’s for (grates under the steps). we will check the other side of the plenum, just haven’t gotten back under there again yet!

[bsmith0404]

I misunderstood where the heat was coming from, I thought you meant the AC return ducts in the ceiling.

As for the low air flow in the bedroom, I’m not that surprised. With the change in levels, I’m assuming there is more dryer duct somewhere in a wall that vents air from the main ducting up to the ducts in the bedroom and bathroom. That’s not an efficient way to move the air and the majority will most likely get pushed out into the living room and kitchen, path of least resistance. I would expect if you added dampened registers to limit the air flow in those areas, you would get more to the back. Also, add dampers to the ones going into the pass through storage.

[ChuckS]

You can block off those stairwell return grills year round.. all it does is allows some cabin air to be expelled via those floor vents into the basement area.

They do nothing as far as returning air to the furnace and they don’t do a thin as far as allowing cooling air to the furnace when in operation

What those floor vents do is allow cold air in the winter and hot air in the summer to blow inside

The furnace gets all the cooling air and such via the vast space under the flooring area since your furnace is mounted under the floor .. some alpines have the furnace mounted above floor behind a cabinet , etc

For furnace control the furnace is usually wired into Zone 1 roof AC control module and that is why you only see furance option on one zone

Some here will argue you must have the stairwell vents unobstructed when running the furnace ..

In nine years if use on my Alpine with the stairwell vents blocked since day one I’ve never had a furnace issue and never had it overheat..

Also your Heat pump will not do anything if the outside temp is below about 36 degrees .

A video I made showing what the stairwell furnace return vents do and don’t do

https://youtu.be/lfY5-egoLz0

Also with the FL model many Alpines owners have needed to rework the furnace ducting furthest from the furnace to include a different airflow divider and larger ducting to the area not receiving much airflow form the floor vents