AboutJ Cook Expertise With 25+ years experience, I am familiar with residential, commercial, and industrial HVAC equipment including but not limited to boilers, chillers, reciprocating and screw compressors. I am trained in all manners of control wiring.
Experience I currently have three HVAC licenses and Refrigeration license by the State of North Carolina. I have been in this field for over twenty years. I have been a service technician for a contractor and also worked at a state college in the repair and maintenance of steam lines and equipment. I am currently the Building Maintenance Superintendent for a municipality.
Question QUESTION: I live in Minnesota and last year bought a 30 year old, 1800 sq. foot 2-story townhouse. New windows and doors were put in about 4 years ago. The furnace and AC appear to be the original ones. Due to design issues, I can only replace it with an 80% efficient furnace. I will get a two stage, but am not sure if the variable speed blower is worth the extra money, as I normally don’t run the fan all the time. I’ve had several dealers out to give me estimates, all representing different brands. One NATE certified tech measured the current TESP of the furnace at 90, and recommended some ductwork to be done during the installation that would bring it down to 80, which was the best he felt he could get with the existing ductwork. Another NATE certified tech said he would do a TESP after installation, but felt sure he could get the reading close to 50. Please enlighten me on the TESP, and what it could realistically come down to with a variable speed blower. Also, everyone recommended a 2 ton AC except one, who said 1.5 ton would be plenty. What would you recommend for tons? The AC is only needed for about 3 months/year.
ANSWER: Paula I am sorry to say, but I would be skeptical of every one of these contractors. With the installation of new doors and windows, the load calculation for this structure has changed. The only way to determine the proper unit size it to do a detailed load calculation. This is a program that any good contractor will have and they plug in the statistics such as insulation, windows, doors, shade, direction the home faces, etc. It is a very detailed calculation and will tell you exactly the size unit required. I am also concerned about it being a two story. Without proper controls, the two levels will never be at the same comfort level as heat rises. I have a two story 100+ year old home and use two units, one for each level. Keep searching and request a load calculation be done. As for a variable speed motor, if it fails they can be $1000 + to replace vs a standard motor which would only be about $100, so I never recommend a variable speed unless a very high efficiency unit is being installed, which I also do not recommend as in my opinion you will never recoup the cost over the life of the unit, especially when repairs are required after warranty. Thanks J
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QUESTION: Thanks for your comments. Do you have any recommendations about the static pressure claims?
Answer Personally I think most of this is blowing smoke. It would require an engineer to test this system to make educated recommendations regarding changes to the duct system as far as static pressure. Duct recommendations can be calculated for the correct CFM's for each supply, but it is really getting very technical when trying to modify static pressures.
