420/44 DB Owners Club

[Alex F]

Thinking about adding louvered vents to the bottom of the door on the guest stateroom. When the door is closed and the ac is on that room is still warm because there is no return for air in that room. Has anyone else done this? Nervous about cutting into that door as i don't down if it will compromise the integrity. It does feel as if its solid all the way through so thinking it would hold up. Thoughts?

Edit: Something similar to this
View attachment 126638

Hey Dean,

I'm no HVAC expert, but I doubt that making a hole in the door will make the room colder. The way I solve this problem is by partially blocking vent in the master, so the air stays on a little longer delivering more cold to VIP stateroom.

 

[Carpediem44DB]

The only way the room will cool is to circulate the air. I think that placing a vent is a good idea as long as the forward stateroom door is left open so the air from the second cabin can get to the return under the bed. If that door needs to be left closed then you should place vents in both doors. I would be nervous cutting into them as well as they are really nice doors but I do think that they are solid.

 

[Alex F]

The only way the room will cool is to circulate the air. I think that placing a vent is a good idea as long as the forward stateroom door is left open so the air from the second cabin can get to the return under the bed. If that door needs to be left closed then you should place vents in both doors. I would be nervous cutting into them as well as they are really nice doors but I do think that they are solid.

I think you just pointed several things here:
1. Just cutting a hole in VIP room's door isn't going to generate circulation.
2. If the master has to have the door open to allow circulation, then we're eliminating privacy.
3. Cutting both doors might improve the circulation, but I'm almost positive that it won't be enough. The VIP vent is the last vent in the line, so there's lots of air flow loss as well as the coolness of the supplied air. On the return side, I'm having hard time wrapping the idea around my head that there will be enough force pulling the return air through tiny holes of two door into small openings under the bed in the master. IMHO, it's too risky with high chance of not getting expected ROI.

 

[Carpediem44DB]

Perhaps the better way to approach this would be to install a return duct in the second cabin back to the HVAC unit under the forward V Berth. I recall tracing the ducting from the unit to the second cabin vent. I don't know if there is enough room in the chases to run a return, but worth a look anyway. The other thing one might try is closing off the in the salon at the dinette thus forcing more airflow to the stateroom vent. One thing that I have noticed on these sport yachts, there is very little serious engineering that goes into the HVAC system installation. The cooling units seem robust and efficient enough but the duct venting and routing leave alot to be desired.
CD

 

[ZZ13]

I’m with Alex. Previous generation of your boat and my guest stateroom stays cool enough with the door closed. My experience says it’s all about room location relative to the cooling unit. Maybe your unit has lost some refrigerant and isn’t as cold as it could be.

I had an addition added to the master bedroom in my house. Single level house with two bedrooms on one end and master in the other end. Open living area in the middle. Only return is in the open living area. After addition talked to hvac expert about adding a return to that room and he said there will be no problem. Gap under door is good enough. But he’d add one later if I wanted it. Ten years later that room still is the coldest in the house. Because the HVAC unit is right above that room. The room gets the coldest air and highest flow.

 

[Irie308]

My thinking is that the air needs to be circulated. The air in the room needs to be removed and conditioned or else new cold air will not over come the unconditioned air. The room belongs to my 14 year old daughter primarily so 80-90% of the time its closed. The forward state room stays open the majority of the time so that's not an issue and when its closed the salon AC is most likely on. If the door to that state room is cracked about an inch the circulation is fine and the room stays cool. I'm sure if you added up the square inch area of what is allowing the circulation at that point it may be 2 or 3 times the area that a vent would allow but I'm thinking it would still be a noticeable improvement. Keep in mind that the return from the salon and the forward state room would be pulling and circulating the air as we tend to run then together. Correct me if I'm wrong but the return vent for the salon unit is probably about 1 square foot if that and it keeps the salon cool. Ideally running a return vent would be the way to go but that seems very difficult. Granted I'm no HVAC tech any stretch, but that's my thought process. I'm also thinking of testing this theory on a warm day by removing the door and putting in a make sift door (plywood or cardboard with the exact vent) to see if their is a temp difference.

 

[Carpediem44DB]

I would think it could be tested by simply cracking the door open 1/2 inch.
The air definitely needs to be circulating to continue to cool. Just like in a house, leave the doors closed to rooms you don’t want to cool and unless they have their own returns, the rooms won’t cool.

 

[NorCalRobert]

My thinking is that the air needs to be circulated. The air in the room needs to be removed and conditioned or else new cold air will not over come the unconditioned air. The room belongs to my 14 year old daughter primarily so 80-90% of the time its closed. The forward state room stays open the majority of the time so that's not an issue and when its closed the salon AC is most likely on. If the door to that state room is cracked about an inch the circulation is fine and the room stays cool. I'm sure if you added up the square inch area of what is allowing the circulation at that point it may be 2 or 3 times the area that a vent would allow but I'm thinking it would still be a noticeable improvement. Keep in mind that the return from the salon and the forward state room would be pulling and circulating the air as we tend to run then together. Correct me if I'm wrong but the return vent for the salon unit is probably about 1 square foot if that and it keeps the salon cool. Ideally running a return vent would be the way to go but that seems very difficult. Granted I'm no HVAC tech any stretch, but that's my thought process. I'm also thinking of testing this theory on a warm day by removing the door and putting in a make sift door (plywood or cardboard with the exact vent) to see if their is a temp difference.

This is my area of expertise and I had the same problem. If your 2nd bedroom door is under cut (inch or 2 gap at bottom of door) so that fresh air entering can push out the stale air that will be all you need for you to have the door closed. The next thing you will need to do is look at your dinette area and you will see a supply register in the deck area between the port side window and the dinette seating, this vent also supply’s air to cabin from the bedroom a/c unit. I removed the vent and installed a air damper to restrict airflow out this vent which will then push more air into bedroom number 2.
I am currently searching for an adjustable air register in the size of the vent by the dinette so I can control the airflow easier than trying to get to a damper that is hidden.
If you want to increase your airflow and comfort throughout (this is a bit more labor intense) you can install hard pipe adjustable KD 90s anywhere the flex duct makes a turn. This will reduce the static resistance of the airflow caused by poor duct design and the increase in airflow will mix the air better throughout which results in greater comfort throughout.
Just because it’s called flex duct and it can flex does not mean it is best to flex it. The most common air duct size is 6 inch and 6 inch also has the highest static resistance to airflow when you either bend/flex it 90 degrees or you allow the inner duct to sag/ripple instead of pulling snug eliminating the ripple inside the ductwork, you want to make it a smooth airflow.
I know it sounds trivial and you may not think it makes much difference but I can assure you the Shitty duct design on our boats has 4 to 6 times the static resistance of a average residential air duct system and for comparison purposes 99% of all residential air duct systems have poor to shitty airflow in comparison to what they could have if the duct design was done correctly.

 

[Carpediem44DB]

I knew you would pipe in Robert. One of the projects on the 506 is to better engineer my HVAC ducting. I'll be bending your ear for some tips whenever you swing by Benicia this summer.
CD

 

[Mark.60]

I had the medicine cabinet and panel behind the master TV out. Looking for broken wire to CO detector. The flex duct to the VIP room is long and has way to many bends in it.Not to mention some of the bends are kinked. I was thinking of a small quiet blower. Like a small bilge blower to force air through the duct.

 

[NorCalRobert]

I had the medicine cabinet and panel behind the master TV out. Looking for broken wire to CO detector. The flex duct to the VIP room is long and has way to many bends in it.Not to mention some of the bends are kinked. I was thinking of a small quiet blower. Like a small bilge blower to force air through the duct.

By correcting the ducting and using adjustable metal KD 90s and keep the flex duct straight and snug it will reduce static and in turn increase airflow and then if need be you can go into the a/c programming and reduce blower speed if you choose

 

[techmitch]

This is my area of expertise and I had the same problem. If your 2nd bedroom door is under cut (inch or 2 gap at bottom of door) so that fresh air entering can push out the stale air that will be all you need for you to have the door closed. The next thing you will need to do is look at your dinette area and you will see a supply register in the deck area between the port side window and the dinette seating, this vent also supply’s air to cabin from the bedroom a/c unit. I removed the vent and installed a air damper to restrict airflow out this vent which will then push more air into bedroom number 2.
I am currently searching for an adjustable air register in the size of the vent by the dinette so I can control the airflow easier than trying to get to a damper that is hidden.
If you want to increase your airflow and comfort throughout (this is a bit more labor intense) you can install hard pipe adjustable KD 90s anywhere the flex duct makes a turn. This will reduce the static resistance of the airflow caused by poor duct design and the increase in airflow will mix the air better throughout which results in greater comfort throughout.
Just because it’s called flex duct and it can flex does not mean it is best to flex it. The most common air duct size is 6 inch and 6 inch also has the highest static resistance to airflow when you either bend/flex it 90 degrees or you allow the inner duct to sag/ripple instead of pulling snug eliminating the ripple inside the ductwork, you want to make it a smooth airflow.
I know it sounds trivial and you may not think it makes much difference but I can assure you the Shitty duct design on our boats has 4 to 6 times the static resistance of a average residential air duct system and for comparison purposes 99% of all residential air duct systems have poor to shitty airflow in comparison to what they could have if the duct design was done correctly.

This is maybe the best marine HVAC analogy and advice ever posted on CSR.
Static resistances and properly calculated CFM's are of the upmost importance!

 

[Bruce SEA 993]

I have a question for follks that know about wiring in solar panels. I want to at this point us a flexible and portable 4 panel 300 Watt system. I want to use them in different places in the bridge.

Can I use the cigarette lighter plug or wire directly into the 12V feed under the dash? There is a big cable that delivers power under the dash. My normal inclination would be to run wires down to the batteries. Does it matter if I use the feed that is already there?

On the380DA I ran the solar wires through the radar arch to a cabinet where I mounted the controller and then 4 feet of 12 gauge wire to the batteries. This boat is a bit more difficult to run wires and they are long runs. The gauge is going to be big. I have to do the calculation...

Thanks!

Edit: I just looked up the wire size for the allowable voltage drop on the run to the batteries from the dash. I would need 10 or even 8 gauge wire.

 

[Carpediem44DB]

By correcting the ducting and using adjustable metal KD 90s and keep the flex duct straight and snug it will reduce static and in turn increase airflow and then if need be you can go into the a/c programming and reduce blower speed if you choose

@NorCalRobert, how important is it to use the insulated ducting for such short runs in a boat hvac system since there is little to no cabin insulation anyway? For my bridge system, I used 6 inch vacuum ducting used in industrial dust vacuum systems. It is much more compact and maintains its smooth shape. It has no insulation but I have to believe that the reduced wrinkles adding better airflow will Trump the lack of insulation. Might be a solution for others seeking to improve their system?
CD

 

[techmitch]

@NorCalRobert, how important is it to use the insulated ducting for such short runs in a boat hvac system since there is little to no cabin insulation anyway? For my bridge system, I used 6 inch vacuum ducting used in industrial dust vacuum systems. It is much more compact and maintains its smooth shape. It has no insulation but I have to believe that the reduced wrinkles adding better airflow will Trump the lack of insulation. Might be a solution for others seeking to improve their system?
CD

Static pressure is one of the most important factors in HVAC design. Simply put, static pressure refers to the resistance to airflow in a heating and cooling system's components and duct work. The push of the air must be greater than the resistance to the flow or no air will circulate through the ducts.

Tough search on resistance specs. But there are tons of options out there.

Here is just one https://terra-bloom.com/products/pr...i_4ovhjgJaCvu28bgUBK08QaFxbN8NxAaAlAsEALw_wcB

 

[NorCalRobert]

@NorCalRobert, how important is it to use the insulated ducting for such short runs in a boat hvac system since there is little to no cabin insulation anyway? For my bridge system, I used 6 inch vacuum ducting used in industrial dust vacuum systems. It is much more compact and maintains its smooth shape. It has no insulation but I have to believe that the reduced wrinkles adding better airflow will Trump the lack of insulation. Might be a solution for others seeking to improve their system?
CD

Airflow is the most important factor but yes you will lose some capacity / temp by passing through non insulated duct. Is the non insulated duct you used the aluminum or rubberized duct? If aluminum it will work against you if not insulated due to aluminums ability to dissipate heat

 

[techmitch]

Airflow is the most important factor but yes you will lose some capacity / temp by passing through non insulated duct. Is the non insulated duct you used the aluminum or rubberized duct? If aluminum it will work against you if not insulated due to aluminums ability to dissipate heat

No doubt! HVAC is definitely not my forte, but I am anal about theory and operation with any thing that I get involved with because, "I need to know". Question, are my thoughts correct in that a perfectly smooth i.d. is not conducive to best air flow management because some turbulence is desired and also, to many CFM's can be counter productive?

 

[Carpediem44DB]

Hey Dean,

I'm no HVAC expert, but I doubt that making a hole in the door will make the room colder. The way I solve this problem is by partially blocking vent in the master, so the air stays on a little longer delivering more cold to VIP stateroom.

I used a clear non insulated vinyl tubing. Four lengths non longer than 6 feet just for the bridge windshield vents attached to 24000 BTU AC. Thinking though of using the same in some of the cabin units down the road.

 

[NorCalRobert]

No doubt! HVAC is definitely not my forte, but I am anal about theory and operation with any thing that I get involved with because, "I need to know". Question, are my thoughts correct in that a perfectly smooth i.d. is not conducive to best air flow management because some turbulence is desired and also, to many CFM's can be counter productive?

I am not aware of a drawback to being to smooth and in HVAC the CFM is tied to the air changes per hour for the space conditioned. For residential air conditioning it is 400 cfm per 12000 BTUH and then calculating the btuh needed for the space and matching the airflow with a proper duct design although I doubt that our marine a/c systems meet this.
For many years air ducts were smooth sheet metal pipe and the airflow was great and static was low, the problem was putting these metal ducts in attics and under homes in extremes temps and they were usually insulated to an R2 or R4 level. One problem I have seen with perfectly smooth (such as pvc duct) is when they (contractors / engineers etc) reduce the diameter of the duct which increases velocity without reducing the cfm cause they are usually trying to maintain a specific static and at that point airflow becomes too forceful similar to a hairdryer on high.
Although as with everything here is the exception Check out how they do hi-velocity duct systems with little 2.5 inch ducts and feeding multiples into each conditioned room. https://www.icsny.com/blog/the-pros-and-cons-of-high-velocity-air-conditioning-systems
The white plastic in you picture appears to have too much ripple, here is a link to the alumaflex I was referring to https://store.acpro.com/7-x-10-bare-alumaflex
but the problem with alumaflex is when it’s not insulated it will transfer heat. The goal is to mix the air properly within the room being conditioned so that the temp is consistent throughout and keeping airflow noise at the lowest levels not to be noticed.
Now granted this is much more challenging on a boat.
Here is a info link https://www.energyvanguard.com/blog/what-happens-air-flow-ducts-when-size-changes/

 

[NorCalRobert]

Static pressure is one of the most important factors in HVAC design. Simply put, static pressure refers to the resistance to airflow in a heating and cooling system's components and duct work. The push of the air must be greater than the resistance to the flow or no air will circulate through the ducts.

Tough search on resistance specs. But there are tons of options out there.

Here is just one https://terra-bloom.com/products/pr...i_4ovhjgJaCvu28bgUBK08QaFxbN8NxAaAlAsEALw_wcB

I did not see the link to the duct in my first reply. Since this duct appears to be lined with Astro foil insulation I would be willing to try this in a boat application since I can’t believe we could do it any worse than what we have currently and I could easily do before and after static test