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Advice please >installing central AC Hi vel, should system include reversing valve for heat pump???

Installing 2 zone central AC on old house with steam heat- Unico air handlers and Lennox xc14 outdoor units. 2 ton downstairs, 4 ton on third floor. Current quote is for AC only. Current steam heat works well -has massively oversized 50 year old boiler. Contractor says AC system alone will probably be a bit more reliable than using a heat pump. Quote started with 14acx compressors until I pointed out the longer warranty and quieter unit. Contractor seems like a good guy.

Would it make sense to go to xp14 units and get some heating use on 50 degree days?? I know we don't talk; price, but as a percentage I would not think the xp14 would be much more than an xc14. Is a heat pump system much more complex than an AC only system? Please help


  • JUGHNEJUGHNE Member Posts: 7,458
    In my experience I have seen heat pumps suffer more as the OAT drops. The defrost cycle puts some strain on the entire system IMO.
    If you have no back up heaters in the ducting system then the system would have to blow cold air, just like an AC, while it is in defrost mode. You could have T-stat controls that would lock out the heat pump at say 40-45 OAT to avoid the need for defrost.

    4 tons for the upper floors sounds pretty big??
    Considering the boiler is oversized for heating based on the building envelope, could the upper AC be the same situation??
  • KoanKoan Member Posts: 436
    I know - I thought that as well but that seems to be what the Manual J suggests. The AC install is new so they are not related. I think the contractor is competent. Sounds like maybe he was on the mark with the HP vs AC. ok - here is another question if you do not mind - does going up to an XC16 compressor (2 stage) from an XC14 make any sense with a Unico system - or is there no possible gain in efficiency? Thanks!!
  • JUGHNEJUGHNE Member Posts: 7,458
    Someone here would know. Not familiar with that equipment......beyond my pay grade.
  • AMservicesAMservices Member Posts: 543
    Your going to zone a high velocity unit?
    Are you using unico's E.C. (variable speed) air handler?
    What's the square feet of the space your conditioning?
    With high volcity you need 6-7 2" outlets per ton. I would have between 24-28 supply outlets. They do have a 2-1/2" supply duct to help reduce the number.
    There needs to be a minimum of 10 ft flexible ductwork between the supply Outlet and the trunk line. That goes for the return duct too or you will have noise problems. Even if the supply is 1 foot away, you need to coil the flex or it will sound like a jet taking off in your house.
    If you don't go with a 2 stage compressor and the system is always running at a 4 ton capacity, you will need 24 supplies per zone or you run the risk of freezing when only one zone is calling.
    Zoning high volcity is tricky and the equipment is expensive.
    The ductwork will make or break the installation.
    You should call unico and talk with there tech support. Let them know what you want to do and find out what they recommend.
    Is your contractor experienced with unico?
  • KoanKoan Member Posts: 436
    Hi. And thank you for your replies. We had a contractor do this install and so far it seems to have gone very well. We used a 4 ton unit for the top two floors and a 2 ton unit for the first floor. Single stage Lennox compressors and Unico inside. It was expensive, but I think it was worth it as the contractor was excellent and clearly had experience with Unico and would verify everything with them if needed. Now we are looking at insulating before we button up all the cut outs needed to run ducting. Do you have any suggestions? This is an old 1928 end of group 3 floor townhouse with some blown in cellulose that has settled. We could get in many of the areas now to lay batts or spray foam. The foam makes me nervous though I assume it is superior.
  • AMservicesAMservices Member Posts: 543
    That's great your contractor is experienced with unico.
    Spray foam is the best. I've worked in attics before and after foam went in and I'll say the difference is night and day.
    Maybe with the money you saved not going with the heat pump, you can make your steam more efficient, turning it into a vapor vacuum system
  • KoanKoan Member Posts: 436
    What should I look for in an insulation contractor?
  • KoanKoan Member Posts: 436
    Sorry for bugging you... I assume all the old loose cellulose should be removed first???
  • AMservicesAMservices Member Posts: 543
    Don't remove anything unless the insulator says it needs to be.
    I'd be looking for a company that's been around for awhile, has good review and is insured.
  • KoanKoan Member Posts: 436
    thank you for the advice, makes good sense.

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