Replies

1. 
   Art_B | May 07, 2001 04:09pm | #1

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   Your HP contractor is giving you good advise.
   The heat pump is not much more expensive than the AC alone. Down to about 40 to 45 F it is less expensive to run the HP vs. gas or propane (at 7.5cents kwhr and 74 cnets therm gas).
   Have heated with wood for 25 years, wife finally said she didn't like to split 14 cords/year anymore, put in HP last year, should have done it 15 years ago.
   However, 3 units? My house is 4700 ft sq, and a single 4 T unit keeps house warm down to about 25 F (very seldom below freezing in PNW)but as above, your radiant should be set to come on at 40F outside, etc (every case is different)
   (I'll forward a spreadsheet I used that you can revise to your e-mail separately)

1. 
   BrianGale | May 07, 2001 04:57pm | #2

   *Arleen-Check out http://www.unicosystem.com. Air handler and cooling coil (modular system) go in the attic or crawl space, and 2" diameter insulated tubes can be run through walls and attics to deliver the cooled air. Air return with filter mounts in the ceiling, AC compressor goes outside. System can also be fitted with hydronic heating coil, so you can warm the air in the house on those chilly days without waiting to heating up all your slabs.I have not installed one- (so I can't comment first hand on performance or noise)."This Old House" has used them on several shows they have done. It is referred to as a Hi-Velocity system. I have watched it installed on the Unico video and it looks fast, efficient, and straightforward.Good luck-Brian

1. 
   Arleen_Niblett | May 07, 2001 09:27pm | #3

   *Thank you Art, for responding. Do you know how efficient heat pumps are when using them for air conditioning when the temp spikes up to 105 degrees? That is when we will need it the most, and I am concerned that it might not be able to cool the house as efficiently as an air conditioner. I am less concerned about using the heat pump for heating, because our hydronic radiant floor heating system should take care of that need, with our backup fireplaces for quick warmth. (We have radiant floor heat where we live now, and I would NEVER use any other type of heating on a permanent basis....it's wonderful!) However, it would be nice to know we have a back up if the fuel (diesel) we use in the boiler ever becomes scarce, but I don't want to sacrifice cooling efficiency to get this back-up heating. The reason we will have 3 units is because of the way the house is zoned, and the restrictions of running ducts exactly where we want them. The idea is to have smaller units operating for just those zones that we are occupying.

1. 
   Arleen_Niblett | May 07, 2001 09:29pm | #4

   *Thank you Brian. I would be interested in hearing from someone who has installed the Unico system. I am familiar with it, but our contractor is not.

1. 
   Art_B | May 07, 2001 11:27pm | #5

   *Arleen:Your HVAC contractor should be able to give you the curves for the type unit you are looking at. Most manufacturers publish data for outdoor temp of 75 to 115F in 5 F steps for 71, 67 or 63F register air for 80F indoor air return, your contractor should have those data sheets for the units you are comparing.

2. 
   Crusty_ | May 09, 2001 07:19am | #6

   *I've never heard of a heat pump not being more efficient than an air conditioner. The only knock on heat pumps is the temperature of the warm air falls as the outside temp approachs freezing so you have to have "backup" heat to stay comfortably warm. Efficiency of heat pumps is given as SEER rating, the higher the better. An SEER of 10 is pretty common now. A 12 is available, but possibly not worth the incremental cost.

2. 
   Arleen_Niblett | May 09, 2001 07:19am | #7

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   Hello all: We are building 5000 sq ft, 3 story house. Summer temps can soar with moderate to high humidity. Winter temps dip into the high 20's, but usually warmer, with some snow. Elevation around 2500 ft. Lowen windows, good insulation, tight construction. State of the art radiant floor heating, all levels, Wiesmann(sp?) boiler. Bottom floor, concrete slab. Top two floors, lightweight concrete over subfloor. Our contractor has done a good job of designing and zoning this system. We're also installing Xtrodinaire woodburing fireplace in great room, and two propane fuel gas fireplaces in library and master bedroom. We NEED air conditioning for a couple of months at least in the summer, so we're putting in a duct system also (sigh). We also plan to install HRV and some type of air cleaner, so would need a fan system for that. My question (finally!): this contractor (a diff one then the radiant guy) has suggested that we should put in a heat pump instead of an air conditioner. Actually, with our large house it ends up to be be three units. I am beginning to question our sanity! Comments, suggestions greatly appreciated. Pros and cons of heat pump vs air conditioner in this situation? Alternatives to conventional ducting? Thanks.......