In the winter, I get a lot of e-mails from homeowners who are worried about their home's heating system. Their furnace runs constantly — to the point that they're afraid to open their gas bills — but some parts of their house still feel cold. They've added insulation in the attic, installed storm windows, caulked and weather-stripped, but nothing helps.
It could be that the forced-air gas heating has become unbalanced, which leads to uneven and inefficient heating.
When the house was first built, the original layout of its ducts and the capacity of its furnace were carefully spec'd out by doing a heat-loss calculation, thus creating an evenly heated home. But things may have been done to the home over time that altered the hot-air distribution from the furnace, throwing the system out of balance.
Forced air gas heating systems are simple to understand: Air is heated over a flame and then distributed by a fan through ductwork to heat the various rooms of the house.
Mike Holmes finishes the installation of new ducting after renovation. Newer furnaces require smaller ductwork. (Holmes group)
So what goes wrong?
If you go back less than 50 years, houses were built with virtually no insulation — the only thing keeping out the cold was a sheet of foil-backed drywall nailed to strapping on the brick or siding. But in those days, energy was cheap, and huge furnaces pumping out tons of heat into oversized ductwork seemed like a good idea. As energy got more expensive, people began insulating better to keep the heat in and the cold out — but their furnaces and ducts weren't changed.
Maybe the house undergoes some renovations, like a small addition. Let's say during the renovation, the contractor puts insulation in the new outside walls — which is good. But, when he puts on the addition, the contractor runs a duct off an existing one to heat the new space — which isn't good. The new duct runs though an unheated crawl space, but he doesn't bother to insulate it — also not good. And he doesn't recalculate the air distribution. Not many contractors think of it; that's the job of a heating, ventilation and air-conditioning (HVAC) specialist. So, part of the house gets a little cooler while the new insulation makes the other area a little warmer.
Maybe in the renovation, some interior walls are moved. Ductwork that was supplying a 10- by 10-foot room is now supposed to feed a 10- by 14-foot room — so the space gets a bit cooler. Furniture gets moved around, and the return air vent is partially covered, which chokes the furnace.
The house always feels a bit cool, but the furnace is running full time, so the homeowners decide they need to improve the insulation to cut down rising heating bills. The homeowner then blows insulation into the attic, which helps, but now the second floor feels too hot and the main floor is still cool.
So the homeowner — thinking the problem is the furnace — buys a new high-efficiency model. That's great, but the original furnace was sized for those big ducts, and the new furnace, because it is so efficient, should have smaller ductwork. Nobody thinks to change the ductwork.
Maybe new, more energy-efficient windows and central air conditioning get installed. The windows tighten the house and the air gets a bit stale. The air-conditioning coil reduces the amount of air the furnace can suck in and reduces its capacity.
Finally, the basement is finished, and it's heated by extending the ductwork yet again. Some of the damper adjustments — which are installed where branch ducts connect to larger ones and on branches that lead to individual registers — are covered, some are half-closed, and the ductwork is further compromised.
New carpets are installed, but to put down the underlay, the duct boots — the part of the duct that flares out and connects to the register in floor — are moved. Now they don't quite reach the registers and half the warm air blows under the carpet instead of into the room.
Each of these changes affected the how heat was distributed, but no one thought about it. It's no surprise that a house like this has hot, stuffy spots and rooms so cold no one wants to use them.
So what can you do? Check to see if the return air is blocked, if the boots are properly installed, if there is insulation on the ductwork where it's needed, and the dampers are open and reachable. Make sure every joint in your ductwork is wrapped with foil tape, not the stuff sold as "duct tape." Make sure the furnace fan is clean and oiled, and the filter changed, if necessary, and the belts replaced.
Call a contractor who specializes in HVAC who can rebalance the system properly. He'll do a heat-loss calculation, which will cost between $400 and $1,000. You'll get a set of drawings showing you how much air is coming out of each duct (including the return air system) — and the size and efficiency of your furnace. You'll also get some recommendations on what changes might need to be made to even out the heat in your home. You might have to run a new length of duct somewhere, or damper a few ducts, or move a register. But you'll have balanced your heating, created a comfortable home, and possibly saved some money on your heating bills.
Mike Holmes is the host of Holmes on Homes on HGTV. E-mail Mike at mikeholmes@holmes-onhomes.com or go to www.holmesonhomes.com
