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Help with Heat and AC choice for Northern CA

I could really use some help from your wise ones!

We are adding 1000sqft and are sizing an HVAC. This 1000sqft space is a kitchen/family room with vaulted ceilings, a small bedroom and bath. Think of it as a 1-bedroom apartment. The window to wall ratio is very high with the East and South wall almost all windows. There is shading and the architect took into consideration the sun path when placing the windows and designing the overhangs so we can maximize solar gain in winter. This new space connects to the rest of the house in a very open way to the dining/living room (about 550 sqft). The old part of the house is on a 13 year old furnace with alumaflex ducts run mostly through the attic but under the crawl space (rodents) for the master bed/bath (the furnace was installed when we added the MBR).

Standard 2x4 framing (yes, we probably should have gone with 2x6 but we are adding to an existing 2x4 house). The new remodel will have a combination of cellulose and foam insulation at R-19 (ceiling) and R-13 (walls and floors). We live in a moderate climate in Northern CA where the need for AC is just a few weeks a year. Temps in the coldest part of winter go down to mid-30's at night and low 50's during the day. We don't have AC in the current house. We do have one person in the house who has some moderate-severe allergies (living in the house while the addition is being built is causing problems because of the dust).

Originally, our spec called for hydronic radiant heat, but sadly, for various reasons (primarily budget) it fell off the list. Instead we are opting for gas forced air and want to take advantage of air filtration that the system can offer. So now the question is what is the best way to do it.

We think we should add the 550sqft of living space that adjoins the addition to the new furnace and keep the old furnace just to heat the bedrooms (we keep those rooms cold at night and they are rarely used during the day anyway) so will have a new furnace serving about 1550sqft. The HVAC contractor recommended a TRANE XV95 80K 3ton, 2 stage variable speed system with one of their higher end air filter systems.

While in our climate the system will mostly run in the 1st stage, there are times when we would use the system at the 2nd stage for air cleaning - essentially running the unit to clean the air during high allergy season.

For AC, he recommends a Cold Point system

<a href="http://www.coldpointcorp.com/pdf/CNC">http://www.coldpointcorp.com/pdf/CNC</a> SPEC ARI Rev 2 - 2008.pdf

So here are my questions:

1) is that the right size system or is it overkill? Our Title 24 report was for the new addition only and indicated a heat requirement for the hydronic systemof about 40K. Although I haven't run the new calculations, it seems the adding the 550sqft would bring that number up to about 60K. Of course the HVAC person is sizing up as the cost differential is only about $150.

2) Does anyone have experience with the TRANE air filtration systems? Specifically their Clean Effects?

3) We've never had AC so I don't really know the differences, but this system seems outdated. Plus it appears it uses an R22 which is being phased out. The reason he is suggesting this system is because we have very strict city codes for noise and can only have a unit that is less than 64dB. Does one even exist that could meet this requirement? We have lived without the AC for 20 years and don't really need it, but as we age the allergies seem to worsen so we thought we'd take advantage of the switch from radiant to gas forced air by getting AC. Should we scrap traditional AC?

Any advice is greatly appreciated.

Thanks in advance!


  • Empire_2
    Empire_2 Member Posts: 2,343
    I have read your post...well informed.

    Since you have a lot of information to offer, I will address the Q;'s that stand out.  True your air can be filtered to acceptable levels for allergies and it's nice to see someone wanting to diversify their equipment so if one for the main house goes down there is another part of the house to seek refuge.  As far as the heat gain and heat loss, a manual "J" or right "J" needs to be performed to arrive at exact numbers.  As you know this is not a guessing game.  We want the home owner to be happy, #1 and #2 we need to conform to any state, county and local codes.

    While everyone has an opinion, Hydronic applications will only heat or cool the envelope (without additional equipment) while air systems give the options for filtration which you seek, optional zoning, and ability to add humidification which owners of expensive wood floors and priceless Grand Pianos demand.  As far as filtration is concerned, you can acquire a HEPA style filtration as used in most hospital applications and have all the benefit of a residential model in your home.  As usual price is applicable and not to be discussed here.  You are well on your way to the perfect system that will satisfy the needs for your family. 

    Mike T.
  • Jack
    Jack Member Posts: 1,046
    What I've done

    Here at my home in the foothills is to pull the ducted system which leaked like a sieve, and add mini-split heat pumps. I also have gas fired Rinnai wall Furnaces. Both systems eliminate duct or distribution systems. High efficiency, net to the space. It's been a good combination heating and ac.

    My usual disclaimer. I represented Fujitsu and Rinnai for many years, so bias noted. But they work really well.
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