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HVAC, what Bryan Baeumler wants you to know

After a great summer of bunkie building and outdoor work, it’s time for an inside job. Fall is a good time to take a cool-headed look at your home’s HVAC system. That old furnace might finally need replacing – or maybe you’re looking for more energy saving from a modern high-efficiency furnace. Either way, there’s plenty to consider before the job starts. I talked to HVAC expert Bill Wood, president of Appleby Systems in Oakville, Ontario for the details on what you need to know when it’s time for a new furnace.

What is the ideal furnace room size or set-up?

BW: The size of your furnace room really depends on the equipment you’re installing and any storage space you might need. A typical furnace with the filter and return air drop needs 8 to 10 sq. feet of floor space – you also need to provide 24” of unobstructed access to the front for service and filter replacement.

A water heater is approximately 24” round and also requires 24” for servicing. If you have a heat recovery ventilator, it could occupy up to 10 sq. feet of space and it also needs 24” for serviceability. Make sure the furnace room is large enough to include all of the appliances you intend to install, without cluttering things up.

What’s available in high-efficiency furnaces?

BW: Typically, there are four standard models of high efficiency furnaces, in sizes ranging from 40,000 to 120,000 BTUs per hour. Base units are single stage with a PSC fan motor and are typically used in subdivision homes. The other three models are Energy Star products with energy saving fan motors with single stage, two stage and modulating heating outputs. An energy saving motor usually uses only one sixth of the hydro needed to run a PSC motor, so the savings with the Energy Star furnace can be significant.

Single stage furnace

This furnace delivers 100% of the rated heat output on every call for heat from the thermostat. In cooler climates, the furnace needs to deliver enough heat to condition the home when temperatures are as low as -10 degrees F. Much of the heating season is close to freezing, so the furnace is cycling on and off every few minutes. This can cause temperature fluctuations throughout the house.

Two stage furnace

This furnace operates at about 65% of the rated capacity and switches to 100% in colder weather, when required. A two stage furnace is 0.5% - 1.0% more efficient than a single stage. The big advantage to the homeowner is improved comfort.

Modulating furnace

Modulating furnaces can be up to 65 stages and include variable speed fans. These top-of-the-line furnaces deliver precise temperature and comfort levels with the highest efficiency ratings.

How do I maximize the efficiency of my ductwork?

BW: Duct systems should be designed based on the volume of air to be delivered to all rooms and areas in the house, with enough heating and cooling to make them comfortable. A heat loss and heat gain analysis by a licenced HVAC engineer can determine the correct size of the furnace and air conditioner for your home. From there, he will calculate the volume of air that the equipment requires to deliver the proper volume of air to the whole house.

He will then design the duct system to provide the air to individual rooms and areas, taking into consideration the number of twists and turns required to connect ducting to the supply air register. Fewer twists and turns will deliver better efficiency and quieter operation. The straightest route is always the best.

Are there other ways to improve heating and cooling?

BW: Keeping obstructions away from the return air openings on the walls and floors is critical to proper air flow. Most branch ducts will have dampers in the pipe below the floor registers that is used to balance the duct system. In rooms that are not heating or cooling properly, you can gradually damper down the runs in the areas where it is comfortable, and force more air to the runs where it is uncomfortable. In the summer, you should shut off the supply dampers in the basement and the bypass damper on the humidifier.

Dirty furnace filters mean less airflow through the system and lead to equipment failure and discomfort. Homeowners need to pay attention to filters. It is recommended that the furnace be maintained yearly by a licensed gas fitter, but the filter may need replacing or cleaning every three months.

BW: Heat recovery ventilators aren’t mandatory in all new homes yet, but they soon will be. Modern building codes require less air leakage in the structure to ensure efficiency, but this means new houses don’t “breathe” like older homes that had leaking windows, doors and joints. When the house cannot breathe, you will get a buildup of contaminants and gases plus humidity in the air.

A heat recovery ventilator solves this problem by drawing stale air out of the house and replacing it with fresh outside air. The stale air passes through a heat exchanger on the way out, where the incoming fresh air picks up 85% of its heat. Heat recovery ventilators will greatly improve the air quality and comfort in most homes.