I have an almost 30 year old gas furnace. While it works, I assume it is nearing the end of its life and will need to be replaced before long. I'm looking at a variable speed heat pump for several reasons. It will need to be mounted on my roof and want to minimize interior noise, I'm in San Francisco and we're built very close together and I don't want to get a noise complaint after it is installed, and a heat pump seems to me to make sense given the mild climate where lows rarely get much below 40 degrees and the highs only get up into the 90s once or twice a year (summer temperatures are in the high 60s).
I've learned that two critical factors in a successful installation are appropriate sizing and adequate duct work to provide airflow to the rooms. To address the sizing, I have had a formal load analysis from an energy consulting firm (33,819 BTU cooling and 21,260 heating). The load analysis suggests a 3 ton system. The remaining question is the adequacy of the duct work that was designed around a gas-fired furnace. Will the existing duct work support the air flow required for a heat pump to heat and cool my space given that it was designed around a gas furnace? The gas furnace currently does an adequate job of heating the space.
Do I get static pressure measurement with my existing gas furnace system to assess the adequacy of the duct work? Some of the contractors I've contacted quoted a 4 ton variable speed unit without raising the capacity of the duct work. One is very hesitant to put in even a 3 ton system (which is what the load analysis calls for) because of concerns with the air flow. The supply ducts are all in interior walls so I'm not really interested in having that redone.
Any guidance?
I've learned that two critical factors in a successful installation are appropriate sizing and adequate duct work to provide airflow to the rooms. To address the sizing, I have had a formal load analysis from an energy consulting firm (33,819 BTU cooling and 21,260 heating). The load analysis suggests a 3 ton system. The remaining question is the adequacy of the duct work that was designed around a gas-fired furnace. Will the existing duct work support the air flow required for a heat pump to heat and cool my space given that it was designed around a gas furnace? The gas furnace currently does an adequate job of heating the space.
Do I get static pressure measurement with my existing gas furnace system to assess the adequacy of the duct work? Some of the contractors I've contacted quoted a 4 ton variable speed unit without raising the capacity of the duct work. One is very hesitant to put in even a 3 ton system (which is what the load analysis calls for) because of concerns with the air flow. The supply ducts are all in interior walls so I'm not really interested in having that redone.
Any guidance?
source https://hvac-talk.com/vbb/showthread.php?2222920-Replacing-gas-forced-air-with-a-heat-pump&goto=newpost
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