Find out how to keep your HVAC system balanced. Get tips on how to adjust it to stay comfortable in different seasons and learn how many returns your duct system should have.
LESLIE: Well, in most homes, there are some rooms that heat or cool better than others and in a couple of cases, you might even have a room or two that just never get comfortable.
TOM: Well, if that’s ever happened to you, your HVAC system may be out of balance. Here to help us set things straight is a guy who’s always in balance: Richard Trethewey  from TV’s This Old House .
RICHARD: Hey, guys. Nice to be here.
TOM: Well, HVAC, of course, stands for heating, ventilating and air conditioning but it’s the ventilation part that many systems seem to get wrong. They either don’t put enough air where it’s needed or they just can’t quite carry the temperature to the spaces it has to go.
RICHARD: Well, it’s the nature of sort of the process of putting in a hot-air furnace. You know, a furnace is a blower unit that pushes air out through ductwork. And now you’ve got to hope that the first installer that did the job calculated exactly how much air should go to this room, that room or the next room. And so, that doesn’t always happen so right from the beginning, you can often have rooms that didn’t have enough.
Well then you’ve got to take into account what happens to a building. The sun comes in on this side and there’s no sun on the other side and now this side gets hotter or colder depending on winter or summer. And so then you’ve got this whole imbalance thing and so people do all kinds of things; they try to close down registers or at the least case, you try to put in this thing called manual dampers. These are sort of little discs that stick into the ductwork and that’s a hit-or-miss proposition, as well.
TOM: Yeah. And we see those on the duct systems  and most times, people don’t know what they are and they certainly don’t know how they work. And very often, even if they know what they do, the handles are the opposite direction of what you think they are.
LESLIE: What you want, right.
RICHARD: That’s right. Right, right.
TOM: So you never know if it’s quite open or closed.
TOM: So, if you do have a room that’s too cold or too hot, where is the best place to start sort of nailing down the problem to make yourself more comfortable?
RICHARD: Well, it’s the – I’ve also got to remind you that the adjustments you would make for heating season might be different for cooling season. So if you’re going to change these dampers, you may have to go back and change them in the other season.
The thing that’s underrepresented in North American heating and air conditioning is zoning for hot-air systems. And we have multiple air conditioning zones in our automobiles and yet we normally have one thermostat in our house for heating and cooling with a hot-air furnace. And so, zoning is something that’s very viable nowadays; you can sort of – there’s a bunch of choices. And the whole process of even getting them wired right is a lot simpler.
I just saw one the other day that you put the damper in and then there’s just a telephone-jack cord that plugs them together. So even the wiring of that is simpler and that cord can also run inside the ductwork, so you could make different branches perfectly zoned and it’s – I even saw that it has a wireless thermostat, so it’s really cool or hot.
LESLIE: Well it certainly seems like the technology is going in the direction where the owner of the home really doesn’t have to be responsible for the adjusting of all of these. But when does it become an issue of the original installation and when do you bring in a pro to sort of rework the system to sort of get that balance in check?
RICHARD: Well, the problem, Leslie, is many of those systems were done on low bid for the original builder. And then the whole building gets covered up and if the duct is the wrong size duct, you really are in trouble, I mean. So the – at the least case, you can try to do manual dampers; at the best case, you do zone dampers.
And then there are cases that the duct is so small that you really have no other choice but to run additional ductwork or to open up walls and ceilings. But that’s a last, last resort.
TOM: Now, is it always the supply duct – that it’s short – or could it be you don’t have enough return air going back?
RICHARD: Yeah, you’re right, Tom. I mean it’s both. With a conventional system, you need clear balance; the same amount of air that’s going into the room through the supply duct should also be able to come back to the furnace to be reheated through the return duct. And if you don’t, all of a sudden that room that’s under returned, so to speak, won’t get enough conditioning and that’ll be a little bit warmer or colder than the rest of the rooms.
LESLIE: And is it generally one return per zone? Is that how it works or just does it vary on the size of the system, the locations of the dampers?
RICHARD: Well, a conventional system should have one return per room.
LESLIE: Oh wow.
RICHARD: Per room. And then a – these mini-duct systems that we often show on the show, they have one center-return. Just as long as you put the right number of supply outlets into the room, you’ll have plenty of heating or cooling.
TOM: And I think you hit on it right there because in the last couple of decades, the HVAC systems that we see builders put in this country have one return per house or at most, one per floor.
RICHARD: That’s right. That’s right.
TOM: And there’s an imbalance right there, from the get-go.
RICHARD: That’s right. That’s right.
TOM: And you talk about, well, you’ve got to undercut the door and this and that.
TOM: But there’s just no way to replace the opportunity for air to go in and out in the same room, because I think folks think that if they could pump – you sort of pump your room full of the temperature. Well, not really. You have to recirculate that air to raise the temperature up and down.
RICHARD: It has to come back, right.
TOM: If you just don’t move enough air, you’re not going to do the job.
RICHARD: Otherwise, you’re just trying to fill a shoe box. You have to get the air back out of it.
RICHARD: We saw an interesting thing that we did on Ask This Old House: this zoning system that you can make every register its own zone without having to open any walls, ducts or ceilings; these inflatable, pneumatic dampers – sort of like beach balls – that inflated and deflated inside the ductwork that went right up at the registers. And we showed it and it really has been interesting response.
TOM: Oh, very cool. So almost like a balloon that fits inside the duct.
RICHARD: That’s right. Right. Because the challenge is you don’t want to have to go open up ductwork or open up walls to get at the ducts and this was a way that – so you can surgically sort of zone the building without having to open up walls, ducts and ceilings.
TOM: We’re talking to Richard Trethewey, the heating expert from TV’s This Old House.
Richard, before we let you go, you see very often sold these boosting fans that are plugged in at the register level; sort of the over-the-counter solution for homeowners that just don’t know what to do. Do they work?
RICHARD: They work. It’s such a last, last, last resort, you know; to add some additional electrical device to put some heat into it. Yeah, it’s going to send more air through that duct or to that zone but I’d love to see you find a better way than just put another electrical device.
TOM: Always best to get a pro in there that knows what they’re doing and get it fixed once, so you don’t have to deal with it again.
Richard, thank you so much for stopping by The Money Pit. Great advice.
For more tips just like that, visit ThisOldHouse.com and check out the heating section, which I bet is a place you’ll find lots more of our friend, Richard Trethewey.
LESLIE: That’s right. If you’re looking for some more great home improvement information from Richard and the entire This Old House team, watch This Old House and Ask This Old House on your local PBS station.
TOM: And Ask This Old House is brought to you by GE. GE, imagination at work.