Has anyone tried a smart vent? There aren't many on the market, and the ones that are get terrible reviews. It seems the main company in the space is Keen (not the band), and the reviews are not good, with complaints of poor reception from the hub and reports of the vents simply dropping from the ceiling! I also can't tell if their company is failing or just prepping for a re-launch... It's also possible that their vents damaged folks' HVAC units.

Then there's Ecovent, which sounds like a super cool company that would essentially give me an individual zone for every room...at a cost of around $5K.

The temp in my son's room is extremely hard to control. It doesn't help that it only has one vent for a room that's larger than another on the floor with 3 vents. Last year the room was always colder than ours and we'd have to sweat it out to keep him comfortable. This year it's always hotter than ours! With the vent all the way open in his room, it'll be ~78 at night while ours is ~72. If I close it half way, it fluctuates around ~72 while ours is ~74.

So clearly I need a way to adjust this vent on the fly and I don't know how to do it!

I really like the idea of the Ecobee and the room sensors, but I don't know how much it'll help. Sure, it'll average out the temps of whatever rooms I tell it to, but given the example above, if the master is 72 and my son's room is 78, and the temp is set for 72, assuming a matched drop in temp the master won't get heated again until it's 69. That's too cold - especially when we have our 2 month old in there.

How do I get this under control?

Air flow through your house - think about where the return air inlets (registers) are located. How is return air flow affected by bedroom and other doors being open or closed?

Supply air (heated or cooled) is only part of the air handling system. Every cubic foot of air that comes into a room from a heating vent must displace another cubic foot of air that effectively ‘leaves’ the room. Think about how air flows into and out of each room, during daytime and at night.

For the hallways and common/open areas, cooler air will generally ‘fall’ down a staircase while warm air tends to float upwards.

Continuous fan forced air flow through the building tends to mix the air and create more even air temperatures. One method is to set the furnace fan to run continuously on a low speed, forcing the house air to move around and stir, mixing the warmer air with cooler air from elsewhere.

It is not unusual to discover that the ‘cold air’ return vents and ducts are poorly located, too small, have incorrect air flow ratios, or do not properly service some rooms when doors are closed.

I would look first at balancing the air flows such that air temperatures in various rooms are close to matched. When the furnace is actively heating, there may be areas that get warmer, faster. Keeping the circulation fan running should bring the rooms back into temp balance.

I have a whole house air exchanger, which exhausts a steady but modest air flow out of the building while simultaneously drawing in outside fresh air. The heat exchanger transfers most of the warmth from the exiting air into the incoming air flow.

It is common to connect this sort of heat exchanger into the furnace return air ducting, but it can also be ducted directly to specific rooms. In my current and previous houses, the unit draws house air directly from a wall or floor duct in a common area room. Outside air is heat transfered and then flows into the cold air return, mixing with general return air flow from the rest of the house.

Some ventilators can be run on a cycle, such as 20 minutes of each hour. I rigged my furnace circulation fan to run on low whenever the ventilator was running, stirring the house air frequently without running the furnace fan 24/7.

The furnace circulation fan keeps the air inside the house moving, not only reducing temperature differences between areas but also distributing the incoming fresh air. A properly installed air/heat exchanger greatly reduces the difference in smell between outside air and inside air. When I walk into my house, the air does not smell like ‘inside’, it has the same overall freshness as outside. Cooking odors fade within hours. A good kitchen fan exhaust the bulk of cooktop emissions, but if you walk in the front door in the evening and can tell what was cooked for dinner a few hours earlier, a ventilator can make a difference.

Unfortunately I'm aware of all of that from watching countless hours of This Old House and learning many lessons from Rich Trethewey about forced air systems. I have no doubt that our home's system could be better designed, as there are plenty of things about our home that could have been designed better to my untrained eye. Unfortunately - as with so many things - a true solution would be costly. So until we replace our furnace (probably within the next few years, TBH), I'll look for cures for the symptoms.

We've kept the circulating fan running 24/7 for a few years now and that definitely helps. But we do keep our bedroom doors closed at night so our son can get better sleep while he's still young. In the master bedroom we're fortunate to have a return vent on the primary stack. The rest of the top floor has a return in the hallway farthest away from our son's door. As I mentioned earlier, his room also has at least one too-few vents in it. The room is about 12'x12' with a single vent in the corner, which is also the farthest run in the entire house so it probably doesn't have much oomph to it either.

Consider adding a through wall vent to allow return air flow out of your son’s room into the hallway.

One method I have used is to cut two vent openings in the dividing wall between hall and bedroom. One vent is low on the wall, the other is high on the opposite side of the hollow wall. The air can now flow through the room side vent, through the hollow wall cavity, and out into the hallway.

If sound management is a concern and the offset vents allow too much sound transmission, I add a layer of sound absorbing material (fiberglass ductboard or fiberglass duct liner) to the inside surface of the wall cavity. My source for this is sold for trade/commercial duct sound absorption. It is a dense matteted fiberglass material, designed to be installed inside metal air ducts, such as you might find on a large commercial building.

This product is commonly sold for filling hollow wall cavities and dampening sound. the problem is you need to leave a large channel open within the hollow wall for air flow. Fill it too full with sound material and air flow will greatly decrease.

Another source is sound absorbing material sold for automobiles. Some have rubber backing and foam layer, with self adhesive backing. Worst case is you cut open the wall cavity to install the sound treatment, then put drywall up, tape and repaint.

In one place I installed a vent allowing room air flow into a closet, then another vent allowing the air flow out the back of the closet into the hallway. Closets tend to be good at absorbing sound, especially if full of clothes.

A method that is common in home building, which I dislike, is undercutting room doors to allow more gap for air flow. Not only does this force the exiting air to be from the lowest part of the room (coolest air in son’s room), it looks terrible and allows a lot of sound to pass under the door.

With some caveats, it is possible to add localized fan boosters to improve duct air flow. I can recommend Fan-Tech products.

Actually getting the duct booster fan properly installed is often a problem. The ceiling below may need to be cut open, or roll back the carpet and access from above the duct. AC power has to come from somewhere.

Fan noise with a booster can be an issue. I have sometimes installed an oversized inline fan with a speed control to slow down the fan. And/or added a sound absorbing sleeve after the fan. Both add bulk to the duct.

If the room uses a five inch diameter air duct, I might choose a six inch booster fan (low noise model, perhaps with speed control), feeding a sound dampening sleeve with 6 or 8” outside diameter. The inside air path would be five inches or larger, then an adapter tapering back to continue five inch duct to room register. Or just run the six inch ducting the rest of the way from fan to room heat vent/register.

If you are lucky the duct feeding your son’s room may be exposed/accessible in the basement. The booster fan can be added down there, will boost air flow about the same.

Depending on which direction the floor joists run, it may be possible to add a second air source into that bedroom. Extending the existing air feed or tapping into ductwork from a neighboring space. All depends on how the air is moving in the room and how you want to manage/alter the air flows.

I can understand being reluctant to tear into a recently built house, and the disruption that occurs while the work is being done.