Fixing a hot room

My office is the hottest room in the house and it gets unbearable in the summer. This room has a vaulted ceiling where hot air gets trapped in a kind of "heat dome" (see attached photo). The air return is just outside the door on the ceiling in the hall.

Last summer I put heat-reflective coating on the 2 windows in this room and installed an attic fan that comes on when the attic hits 90 F. These changes lead to little improvement with the room hitting over 80 F in the summer. I have force air gas heating with central AC and 1 vent in the room (see photo).

A friend suggested installed a bathroom fan at the highest part of the ceiling (between the smoke alarm and light in the photo) to suck the hot air into the attic or to a new roof vent.

What would be the best way to solve this problem? Options I see are:

1) install a vent fan as described above. If so, then should I vent into the attic or install a new roof vent?
2) install a vent at the highest point in the ceiling and connect it to the return line. Easier to do than #1.
3) Install a portable AC unit in the room. Not ideal due to the noise and might not get the hot air out of the heat dome.
4) Upgrade the furnace blower to push more air.
5) Install an additional vent to get more air into the room.


Ceiling of the hot room

 

Was the room included as conditioned space in the original system design?

Installing a vent fan to expel conditioned air (as hot as it might be) will just put an additional load on the system to condition makeup air.

Increasing air flow in the room by adding a return register might help especially if it is mounted high.

Add a power vent at the supply outlet to blow cool air further into the room.

You also need to take latent heat into account. Once the room heats up it will take a while for the latent heat in walls, furniture, etc. to be dissipated when the system comes on. You will feel it as radiant heat even though the room temperature is cooler.

Where is the thermostat located. It may be satisfied in a cooler room and the system shuts down before the office gets cool.

I have similar vaulted ceiling in a main bedroom in a converted attic. I do not have central air so I installed a mini-split unit. Using a wi-fi connected control that replaces the remote, I have programmed schedules to cool (and pre-cool to limit latent heat buildup) based on time-of-day and room temperature.

 

Have you tried just a window fan to exhaust air? I would try this first, just to see if a large exhaust will lower the temp enough to make a difference. Then based on those findings, determine if a small window A/C might be the most economical method. You could run it before using the room, then vacate the room for a rest when it becomes too uncomfortable and run it again. Also you might want to measure the relative humidity. Too high and it makes you feel uncomfortable.

 

>Was the room included as conditioned space in the original system design?
Yes, although I would say that design was not good.

>Where is the thermostat located. It may be satisfied in a cooler room and the system shuts down before the office gets cool.
Thermostat is on the ground floor, but I have sensors in the upstairs. My system is only 1 stage so the thermo tries to keep the average temp of the house cool in the summer. However if I run the AC enough to cool the office, it freezes out the ground floor which makes my wife unhappy :-(

>Have you tried just a window fan to exhaust air?
Yes, better than that, I tried a portable AC unit which blows out the window. It's loud and can't keep up with the heat on hot days. The portable AC will lower the temp from 83 to 81.

>Also you might want to measure the relative humidity. Too high and it makes you feel uncomfortable.
I live in the pacific northwest and our summer heat is dry. We don't have the hot humid summers they have out east. I grew up in that and do not miss it!

 

I'm thinking the easiest solution might be tp add a vent booster fan like this:
booster fan

Has anyone tried something like this?

 

How about closing off or nearly closing off the dampers on the first floor to direct more cool air to the upper floor?

 

You have the typical 2-story residence with a low cost heating/cooling system.

Heat rises but cool air is heavy and hard to push up stairs especially when the thermostat is on the first floor and it's much cooler down there so it tends to shut down before the 2nd floor is cool.

You don't have a lot of options. Make sure your blower is on high speed, close off as many 1st floor vents as possible to force air upstairs. If that isn't sufficient a small mini split it a cost effective option. Installing vents/fans is not really going to help!.

 

It will help to close the vents (registers) but more important is closing off dampers in the duct work in the basement.
​​​​​​​I think that is what Marq is referring to.

 

I tried a portable AC unit which blows out the window. It's loud and can't keep up with the heat on hot days. The portable AC will lower the temp from 83 to 81.

Please explain this further. Was it an in the widow A/C or a portable roll around with ducts or vents that go through a window? What was the cooling capacity? How many hours did you run it?

I know you dislike the noise, just want to know if it was a legitimate A/C unit. If so, and it did no more than 2 degree reduction you have a bigger problem than just increasing airflow on the existing system.

If it was not a true A/C then I would add a return to the room, add at least another supply vent, and rebalance the system with baffles or dampers at the source. Best option is a mini split if price is acceptable.

 

>Please explain this further. Was it an in the widow A/C or a portable roll around with ducts or vents that go through a window?
Portable roll around that vents out the window.

>What was the cooling capacity?
14000 BTU
> How many hours did you run it?
3-4 hours.

I'm not sure the unit was working properly. The fan comes on and I hear the compressor come on but the air doesn't get that cold and eventually I end up with frost on the coils.

 

>Make sure your blower is on high speed
I've confirmed the blower is on the highest speed.

 

That is somewhat indicative that the unit was not working correctly.

Honestly, a portable AC unit is probably the easiest/cheapest solution. A mini split is more permanent and Id guess that heat is probably not needed as much.

Might consider a new AC unit!

 

I often use an uninsulated 3rd floor attic 'library' as an alternate office- What I've found is-

1) In spring and fall, you want to have the house thermostat set to 'circulate / fan on' if you can to move air around.

2) It sounds like this room faces south- If that is the case, then open the top window ½way, and find a north facing window on the first floor or basement and open the bottom part of that window ½way. Simply allowing a "chimney effect' where the hot air rises and sucks in cool air through a basement window can make a HUGE difference in comfort.

3) If you have an attic, then I'll guess you have an attic access? Is it a pull-down staircase or a simple vent? If you have an attic vent, then allowing the hot air to rise from 1st to 2nd to attic and then exit out the attic will help- BUT you need to allow for replacement air-cubic-feet, BUT that can be done by ½opening a window on a cool northern side of the house.

4) You might add an oscillating ceiling fan and have one pointed at the top of the window, let the other sweep the room. It will eventually mix the air and cool down the room

 

In an ideal world, the system was designed and sized properly to your house. Thats not just the tonnage of the unit itself, but also the size/placements/# of ducts running to each room. Unfortunately, systems often arent sized correctly.

Not sure if you've found a good solution yet but here is what I've done in my system and would check in your situation.

1) Check the air flow out of the office register. Is it Low? Check if there is a damper where it attaches to a supply plenum; make sure its fully open. Is it high/strong? Then the problem is likely a sizing (ie not enough supply ducts or big enough supply duct) or a thermostat placement issue (but you have sensors to offset that).

2) Check the duct supplying the room. How does it attach to the plenum? Sometimes installers put asinine bends and turns in the duct. See if you can straighten it out at all to improve flow. Check the plenum near the office's take-off... are their other supply take-offs on the endplate of the plenum? This can result in poor flow to other take-offs.

2) Check the balance of the dampers at the supply plenum for all your rooms. You can maybe redirect a little less air downstairs and more upstairs. You don't want to close off too many vents though; that stresses the blower and can lead to the coil freezing.

3) Run the fan all the time to keep air circulating and temps more even.

4) Consider a booster fan (as you mentioned). They work but often aren't a great solution. Ideally, the ducts/air handler will be resized to properly supply the zone.


I have a 1920's house that has had several extensions added and, as a result, a Frankenstein hvac system. Room supplies were installed before I bought the house and done based on what they could get to the rooms and fit into the walls and not what rooms necessarily needed. The biggest help is running fan 24/7, for both heat and ac. It keeps temperatures pretty even and fixes the cold or hot spots. I also have long, skinny room that is farthest from the air handler and has one 10" supply at one end. Its 10ft vaulted ceiling with skylights, so it gets pretty hot. Installing a booster fan really helps increase the flow to this room. This is the fan I used. I wired it so it can turn on when the airhandler fan is activated. These fans aren't always ideal as they will throw off the balance and the design of the system, but, if the system is already messed up and not working well, there isn't much harm they can do.