I'm in Bay Area and just bought a new townhouse. The home came with a furnace (of course) and is pre-wired/piped for A/C. The model house had A/C preinstalled. So far I talked to one A/C tech and he mentioned something I didn't quite get -- he said that the A/C must have the same tonnage as the furnace. Is that the case and if so, why?

Furnace: N9MSE0401410A (ICP)
condenser (outside unit): N4A330AKC200
evaporator ("coil"? inside unit): ACE30A24145L087

FWIW, google tells me the A/C is 2.5 ton, which may be kinda low for my square footage (~1500) -- but it's spread out over 3 floors with a climate control zone on each floor.

Another question: assuming the tonnage is correct (2.5) and the fact that I'll probably be getting 13SEER unit (don't usually need A/C except for ~4-6 weeks in a year, so probably not worth the investment), how much should the project cost me? I'll be talking to other contractors to compare, but wanted to get the ballpark figure.
For instance, original builder wanted >$4000 (and probably installs cheapest possible parts); the contractor I talked to wanted ~$3000, quoting ~$2000 for the unit. I get the feeling it's too high, since I see 2.5 ton variable speed 15 seer unit on ebay for about that much (not proof of anything, I know, but the industry is obviously geared to hide everything from the consumer... anyway, that's another topic)


Thanks!

 

The "tonnage" of the cooling coil (evaporator coil) must match the airflow of the furnace blower. Most of the time this is not a problem but sometimes in hot climates a larger than necessary furnace is required to get a large enough blower. I doubt that is the case in your situation.

I AM confused, however. Do you currently have an evaporator coil installed in your furnace? You also mention the condensing unit part number. Do you have both the evaporator coil AND condensing units? Are they connected by the tubing "lineset"? How about control wiring?

 

Ah, that makes sense -- so the blower is reused for both furnace and A/C.. then of course the air flow should match

I don't have an evaporator nor condenser -- but I got the model numbers from the neighbor's house (same floor plan).

 

If your neighbor's house was built around the same time as yours with a similar floor plan and constructed to similar standards of insulation, etc. then a similar sized A/C should be acceptable provided that your neighbor's system performs adequately. Be certain to get several bids (at least three but I prefer five or more) from different contractors. Also get references from the contractors and follow up on them asking the people how they feel about the work that was done and if they recommend the contractor. Remember too that installation is the most important. The highest quality equipment installed poorly is worse than the lowest quality equipment installed properly.