In recent years the manufacturers of forced air furnaces have made dramatic gains in combustion efficiency. Today’s premium models are as high as 98 percent efficient. Can manufacturers make them any more efficient? And even they can, is there any point? The short answer to the first question is ‘maybe’ and, as to the second, it’s doubtful. However, these are not simple questions.

“I really believe the AFUE has maxed out,” remarked Tony Carrillo, national sales manager for the Coleman brand, a division of Johnson Controls, Oakville, Ont. “There’s very little room left to improve gas savings.”

“I think we’re pushing the envelope now,” remarked David Morden, president of Morden National (ECR International/Olsen), Wallaceburg, Ont. “Where you have a combustion product, you’ll never have 100 percent efficiency.”

Well, not likely, anyway. “One of our engineers said 100 percent AFUE is theoretically possible, but it’s probably something no one will ever attempt because it’s just cost prohibitive,” remarked Ian McTeer, field service representative for Trane Canada, Scarborough, Ont.

In fact, for manufacturers today, having the highest combustion efficiency is probably more a matter of bragging rights. Any further gains will be measured in fractions of a percentage point and become increasingly more difficult and expensive to make.
That’s not to say efficiency can’t be improved. While furnaces may not go much beyond 98 percent, it’s likely the minimum will move up, said McTeer. “The way the industry is moving, the 95 percent AFUE will probably be the minimum target.”

As well, while furnaces can reach their peak efficiency at maximum output, there is still room to improve some furnaces at lower stages of modulation. And there are still gains to be made on the electrical side. The Natural Resources Canada (NRCan) Office of Energy Efficiency (OEE) estimates the blower motor accounts for about 10 percent of a typical forced air furnace’s energy use and is one of the largest consumers of electricity in the home.

Manufacturers have made significant gains on this front by going to direct current electronically commutated motors (ECM), which also allow better control and thus more comfort. The days of the traditional permanent-split capacitor (PSC) motors is likely limited.

“The goal in the industry seems to be to have modulating furnaces with DC motors in them. Perhaps that’s all we will have in the future,” remarked McTeer.

Regulations

In 2010 Canada raised its minimum efficiency to 90 percent AFUE, eliminating the mid-efficient furnace option, which is still available in the U.S. One of the biggest headaches for manufacturers is that individual provinces are getting into energy efficiency and making rules that are different from the national standard. Manitoba, for example, has set the minimum at 92 percent for retrofits and 94 percent for new construction. One thing manufacturers don’t want is a patchwork of different standards across the country.

“When you have a more harmonized approach to codes and standards, a manufacturer can more readily justify the research and development because you know it’s going to be a national product,” remarked Dave McPherson, general manager for Rheem Canada Ltd, Brampton, Ont.

The move to 90 percent minimum efficiency has created a marketing problem for manufacturers, he added.

“The difficulty is that manufacturers used to be able to differentiate their product with a ‘good, better, best’ scenario with different AFUE ratings. But when they get so high – everything’s high efficiency – the differentiation becomes more difficult.”
As a result, manufacturers must focus on other factors such as blower motor technology or energy efficiency at different stages of modulation. However, these are finer technical points that can cause the eyes of the typical homeowner to glaze over.

Training is a priority for the industry. This cutaway training rig marries a 23-SEER Frigidaire heat pump with a 97 percent AFUE modulating gas furnace. (Photo by Brian Guttormson)

Retrofit installations

Having high efficiency equipment is one thing, getting to perform at that efficiency level in a home is another.

AFUE ratings are established in a controlled lab environment. In retrofit installations, existing ductwork can be undersized and furnace location can be less than ideal.

“We are just putting a very efficient machine into what may be an archaic air distribution system that may or may not do the job,” said McTeer. Many Canadian homes were built with “cookie cutter 8x18 duct.” It is designed to move 1,000 cubic feet of air at a 1,000 cfm, which may not be adequate. As a result, operation can be noisier and the furnace won’t operate at peak efficiency.

That being said, if the homeowner is replacing an existing 75 percent AFUE furnace with a modern 90 percent plus model, they are going to see a noticeable difference on their fuel bills and also, in most cases, in their comfort level.

As well, improved the insulation and windows may allow the contractor to replace the existing furnace with a smaller one. Ductwork that was undersized at 100,000 Btu/h may prove just right for a 70,000 Btu/h furnace, for example. Furnaces down to 40,000 Btu/h are readily available today.

“For  contractors, the best that they can do is to make sure the unit that they’ve installed is going to work in that duct system. Even if the furnace may not cover the entire heat loss of the home, as long as it will work satisfactorily in the distribution system you have a better chance of it heating the house properly. An oversized unit and a bad duct system is just going to cycle on the limit and it won’t heat the house,” said McTeer.

Commissioning in July

One of the biggest issues for manufacturers is training technicians. While the manufacturing and testing processes have reached a point where factory defects are rare, the new high efficiency furnaces are considerably more critical to set up.

 “(With high efficiency furnaces) there’s a lot more being asked of the contractor,” said McTeer. “It’s not something you can just slap into place, set it and forget it. Some of the new electronic controls can help the installer with the setup, but they really do require the proper airflow, the proper gas pressure. You can skimp on those parts of the setup.”

McTeer admits that sometimes it’s not easy to run the furnace for a full 15 minutes before doing the checks. “Who’s going to turn on a gas furnace in July, let it run for 15 minutes and do all these measurements?” In theory, the technician should come back to commission the furnace properly in the fall, but contractors seldom make enough profit on the job to afford a special commissioning call.

Efficiencies may have peaked, but that doesn’t mean furnace development will stop. Heating appliances will likely get smaller, manufacturers will look at different materials for construction, will focus on getting every stage to a high level of efficiency and will look for savings on the electrical side.

All these add up to better efficiency and comfort for the homeowner. And, at some point, high efficiency furnace technologies and their electronic controls will become commonplace for the contractor and they will reach the top of the learning curve. But it’s likely to be a struggle for a while yet.