www.hvactechgroup.com - forums

Looking for opinions from the guys with residential experience.
Changed my furnace 2 or 3 years ago. No problems with the 1997 Lennox. Just old.Put in a Luxaire 2 stage with multi-speed ECM. No issues. Also installed a new 2.5 Ton cased coil with the intention of replacing condensing unit the following spring. Never happened. Hooked the existing 2 ton R22 Keeprite condensing unit back up. Not having any issues.
Thinking now about installing a MITSAIR add on heat pump and connecting to existing coil. MITS says their outdoor unit is compatible with any coil.
What do you guys think? I'm Thinking more about comfort, that I hope will come with inverter duty compressor, than energy savings.
Good idea? Bad idea? If good, do you recommend 2.5 ton to match coil or 2 ton? Kinda always thought existing AC was borderline at best.House is poorly built cookie cutter 1997 1800 sq ft.
I work in commercial/ industrial service. Figure some of you guys know this way better me.
Thanks for input and sorry for long post for short question.

It always starts with a proper heat loss/gain calculation.  There are some decent programs that will get you close for free...it's better than nothing.  Size your heat pump to the cooling load trying not to exceed it by much more than 30%.  Variable speed equipment provides a narrow margin of error here so if your true cooling load is close to 2 tons I might stretch it to a 3 ton variable piece of equipment to maximize heating capacity.  Some equipment gives the option to dip switch down from 3 ton to 2.5 which might be preferable, especially on the latent capacity side of the equation (something I think is way overlooked when it comes to actual COMFORT).  As for hooking the MitsAir to your r22 coil, if you're in refrigeration I needn't bring up that mixing oils is not a good idea, even if you rx11 flush it, I wouldn't make that gamble.  I cannot stress the importance of airflow enough in retrofits.  Use one of the many methods to get a good estimate on what your actual airflow is and size your heat pump to that if its less than 2.5/3 tons. 

Thanks. Good reply. I can do a heat load and measure air flow easily enough. I had considered over sizing to gain heating capacity. Maybe I will based on air measurements.
Thanks again.