That Old Furnace

1. That Old Furnace You just bought a house and can't wait to move in. Your home was inspected and no major concerns were observed. As with most home inspections a list of repairs was presented with the home inspection report. Many of these repairs represent a continuation of the ongoing maintenance involved with home ownership. This will determine just how big your "honey jar" or "to do" list will be. It's good to know just how much maintenance you are "inheriting" with your new home. In the heating section of your home inspection report you were informed that the furnace responded satisfactory to controls but it would be wise to replace this 30 year old furnace with a more efficient model Airco. So if it works, why replace it? While Lennox Industries first introduced the high efficiency furnaces in 1982 and were touted as being 98% efficient, typical furnaces of that era had efficiencies of 65% or less, many of which were just short of being "tanks" but capable of lasting 40 years or more. The quick math shows that you can save 33%, when I replaced my furnace I realized a savings of closer to 50% on gas consumption. This was accomplished by the fact that I replaced my "tank" which was an old Airco that had a Btuh rating of 108000 Btuh with a Coleman high efficient furnace with a Btuh rating of only 60000 Btuh. The original 108000 Btuh furnace was way over sized and makes for very inefficient operation. Properly sized furnaces operate much more efficiently. That's the first good reason. More reasons to follow... Today's furnaces can also offer two stages of heating capacities again increasing the efficiency operation by using less than full furnace capacity on warmer days when less energy is required to heat the home. For example 40000 Btuh on low fire for warmer days and 60000 on high fire for colder days. Variable frequency drive motors is another option in furnaces that offer electrical operating efficiency. These motors "ramp" up to speed and are extremely quiet. Speeds can be separately adjusted for heating, air conditioning and continuous fan operation. Furnace replacement also offers the opportunity to improve air filtration with readily accessible filters mounted exterior to the furnace. I recommend a minimum MERV 7 filtration rating and prefer a 4 inch wide filter. Typical sizes are 4x20x25 or 4x16x25. Your furnace return air duct should also be connected to the exterior of the home with an insulated duct to provide a source of fresh air when the furnace fan is operating. This greatly improves the indoor air quality of the home as it is mixed, heated and distributed throughout the home via your duct system. NOW, since high efficiency furnaces cannot be vented with the existing B-Vent chimney, this chimney should be downsized to accommodate the Btuh rating of the gas water heater. This is easily done with a flexible aluminum chimney liner dropped down inside the existing B-Vent. The reason this is done is to

2. assure proper venting of the water heater. This very often over looked with furnace replacements. Oversized chimneys will cause condensation of the flue gases and are more prone to down drafting. High efficiency furnaces are typically vented to the exterior with plastic pipes, one pipe for the exhaust products of combustion and one pipe to supply air to the gas burners. With a two pipe system you are using outdoor air and not using expensive heated indoor air to supply to the gas burners. High efficiency furnaces will also require access to a waste water line as they produce condensate from the products of combustion. This condensate should not be disposed of into cast iron or copper waste lines as it will corrode these metals. If your waste water lines are not plastic then this condensate will have to be neutralized prior to disposing to prevent corrosion of the metal waste water lines. These are the basic consideration when replacing that old furnace. A more comprehensive evaluation can be offered by your local heating contractors.