Sloped ceiling - remove hot air with exhaust fan

Question

I have what I think is an unusual setup of a sloped ceiling that may offer an easy fix to my problem, but wanted to get some opinions from you guys.

Our master bedroom, on the 2nd floor (top floor), has a sloped ceiling (roof above it) and also a wall that is 2 stories high. So it's a square room except 1 wall is 2x the normal height, and therefore the ceiling is sloped. The master bedroom faces west, has a large window on the short wall, and gets pounded with sun all afternoon. It gets up to about 80-82º. It's nearly impossible to get it cooled back down with the existing single duct. The upper part of the tall wall has an unconditioned attic on the other side of (behind) it.

The 2 other bedrooms on the 2nd floor have normal flat ceilings, with the attic above it. Those 2 other bedrooms are facing east. They stay nice and cool in the summer.

About 5 years ago, we had new insulation put in the house: loose fill in the attic, and dense pack in the master sloped ceiling. They did not install air ducts (baffles?), so I think the insulation is just really packed in. Works well for keeping it warm in winter. But now it's hot in summer.

I've tried adding an in-vent fan that constantly pushed air in the room. That helped a tiny bit. I installed a blackout shaded, which keep the light out well, but has not helped the heat build up.

I'm having some HVAC people come to give their opinions on what can be done, but I wanted to get your thoughts.

One idea: add another duct from the basement blower unit up to the master. This will be costly I'm sure. Will this help solve the issue?

Second idea (maybe a bad idea, I don't know, please tell me): The upper part of the tall wall in the master has the attic on the other side of it. So, would it make sense to install a simple bathroom exhaust fan high on that wall, that sucks the hot air from the top of the room and dumps it into the attic (or out to the side of the house)? With the attic setup, looks like it would be easy to install and hook it into a light switch in the master bedroom.

That unusual setup of the high wall that has the attic on the other side of it - seems like a good opportunity for a simple, inexpensive fix to the problem (exhaust fan). What do you guys think?

Any other thoughts about options that would be most effective in getting rid of that trapped hot air?

Thank you!!

Answer 1

I usually advocate for a small mini split air conditioner in your case. For less money you could go with a portable unit in the master bed. The problem with adding a new duct is it will imbalance the system if the rest of the house is good. Also when you go to heat in the winter you will get twice the heat up there. As far as a fan up high, I think you will need a whole lot more air flow than a bath fan can move. Also you will then be dumping all your cooled air outside. Shouldn’t work well but I have seen things like this that shouldn’t be a good idea on paper work out due to other factors.

Answer 2

Exhaust into Attic I would be willing to give this a try. Search for "Through-the-Wall Exhaust Fan" to see examples designed to vent directly through a wall. For a given CFM these will be both more effective and quieter than a conventional ceiling-mounted bathroom exhaust fan.

This sounds like a good solution for the summer. At least it can't hurt. You may still need to put in a split-AC unit as advocated elsewhere. If there is a bathroom that opens onto this room one concern would be humidity getting pumped into the attic if you are not using your bathroom exhaust fan. (So use it). In the winter I would be concerned about warm air leaking into the attic and cold attic air leaking into the bedroom. I would look for fan with louvers to minimize this.

Address the heat source Rather than pump out the heat consider ways to avoid it to begin with. Depending on you location and the geometry outside your window a combination of awning and/or a tall tree or a hedge might shade the window from the worst of the afternoon sun.

Instead of black-out shades on the inside of the window install shutters on the outside. There are the traditional (in the U.S.) kind on hinges to right and left of the window. Then there are the kind that are popular in Europe that roll down. In either case, because the shutters are outside the window the heat they block never gets into the room.

Finally, you could replace the window with one that has an aggressive heat-reflective coating. What's right for your situation depends on your geographic location (angle of the sun and need for summer vs winter performance). Local window installers will be able to recommend options. Note that the more aggressive coatings let in less visible light (which you may or may not want). Also, they tend to have a noticeable tint or mirror-like reflection. This may make the window look odd or stand out from outside. The more modest (E2) coatings are hard to pick out from uncoated windows.