Roof Vents Open or Closed When Running A/C?

gotsmart wrote:

PackerBacker wrote:
Well the hot air should expell through the ac unit but I also leave the vents open just for additional fresh air. My vent have fans in them so leaving them open simply allows me to turn a fan on when needed for places like the bathroom and kitchen area.

If it's very hot and humid, I will sometimes close the vents.

I know that at home, we keep everything shut when the ac is on but we don't have vents there.

Some folks may be confused by the fact that the dashboard air conditioners in many vehicles also pull in fresh air from the outside. It can act as an air exchanger in addition to cooling. Thus cracking a window open allows it to push out hot cabin air and cool the interior faster.

The roof AC in an RV is a closed system (at least the ones that I know of). Just like a window AC in a home, it does not draw in outside air. Opening a roof vent fan doesn't help much unless a window is opened to pull in outside air. This will bring in fresh air, but the trade-off is increased workload on the roof AC.

A roof AC is already drawing in hot air at the ceiling and is pumping out the cold air - which sinks to the floor. Oscillating floor fans would serve to better distribute the cold air throughout the RV than roof vent fans.

Possibly the better roof vent fan solution to use with AC are fans with "dome closed" operation like these Shurflo fans. They can recirculate the interior air by running the fan with the vent cover closed. Granted it is a vertical column of air, but at least it doesn't have to draw in outside air.

I agree, I just like having the vents open and I run the fans as needed.

Up north here in the Airondacks it usually cools off enough at night that the ac's don't kick in (I leave them on 'auto'). I find that the open vents just provide us with some fresh air without opening a window. :C

... Eric

PapPappy wrote:

WoodGlue wrote:
What about having a Fantastic Fan on (exhaust setting) for part of the time?

WoodGlue

Well, where do you think that "exhaust" air comes from? You are still drawing air (and humidity) into the RV through other cracks/openings in the RV, to exhaust them.

Better to use the vents in the evening, when you don't use the A/C, but keep in mind that the whole purpose of A/C is to reduce humidity, which in turn helps to remove the heat from the air. Every time you open the door or a window, you are letting that warm humid air back into the RV, causing the A/C to work a little harder....much the way that you effect the fridge, every time you open the door to look inside.....the more the system is contained, the better it's going to work:)

Thanks for the info!

WoodGlue

Mine are usually open for a while (5 or 10 minutes), then closed, unless I forget! Same principle as car, leaving a windows open at top for a few minutes helps to exhaust the hot air quicker initially, but then closed to help AC dehumidify.

Closed. No need to cool the great outdoors.

mr. ed wrote:
I very rarely run A/C since I spend most of my time in the dry southwest. Now that I'm located in Arkansas where temps and humidity are high I find that I'm running my A/C almost daily . My common sense tells me to leave the roof vents open at least a little to allow hot air to escape since the cooler air will remain at lower levels. However, in experimentation it seems to work a little better with them closed. What about you? Vents closed or open?

PackerBacker wrote:
Well the hot air should expell through the ac unit but I also leave the vents open just for additional fresh air. My vent have fans in them so leaving them open simply allows me to turn a fan on when needed for places like the bathroom and kitchen area.

If it's very hot and humid, I will sometimes close the vents.

I know that at home, we keep everything shut when the ac is on but we don't have vents there.

Some folks may be confused by the fact that the dashboard air conditioners in many vehicles also pull in fresh air from the outside. It can act as an air exchanger in addition to cooling. Thus cracking a window open allows it to push out hot cabin air and cool the interior faster.

The roof AC in an RV is a closed system (at least the ones that I know of). Just like a window AC in a home, it does not draw in outside air. Opening a roof vent fan doesn't help much unless a window is opened to pull in outside air. This will bring in fresh air, but the trade-off is increased workload on the roof AC.

A roof AC is already drawing in hot air at the ceiling and is pumping out the cold air - which sinks to the floor. Oscillating floor fans would serve to better distribute the cold air throughout the RV than roof vent fans.

Possibly the better roof vent fan solution to use with AC are fans with "dome closed" operation like these Shurflo fans. They can recirculate the interior air by running the fan with the vent cover closed. Granted it is a vertical column of air, but at least it doesn't have to draw in outside air.

We are in the middle of a hot, humid spell and our air has been running for about a week now (we are in MI). We are parked on the mgr site (direction not our choice) and the sun comes up at the rear and moves overhead and then down in the front. We are in the sun all day. We have noted that there is a lot of heat that comes thru the vent covers (closed) from the sun. We have now put our insulated pillows used in winter in the vent openings and it has help to keep the inside cooler. So no, we would not have the vents open to let all that hot in from the sun overhead.

WoodGlue wrote:
What about having a Fantastic Fan on (exhaust setting) for part of the time?

WoodGlue

Well, where do you think that "exhaust" air comes from? You are still drawing air (and humidity) into the RV through other cracks/openings in the RV, to exhaust them.

Better to use the vents in the evening, when you don't use the A/C, but keep in mind that the whole purpose of A/C is to reduce humidity, which in turn helps to remove the heat from the air. Every time you open the door or a window, you are letting that warm humid air back into the RV, causing the A/C to work a little harder....much the way that you effect the fridge, every time you open the door to look inside.....the more the system is contained, the better it's going to work:)

I will initially leave the vents open and maybe even open up some windows to let the breeze drive out some of the hot air and then close them.

What about having a Fantastic Fan on (exhaust setting) for part of the time?

WoodGlue

Well, that explains why I felt it works better with the vents closed. I so rarely use A/C that I just had to ask the question. Out west I find a fan is sufficient to keep me comfortable. I'm happy that electric is included in my present monthly site. Let her rip! :)