Furnace and indoor coil must be matched to outdoor unit. For so many zones, esp when upstairs mbed is a zone by itself, a 5-ton system causes many problems. 1. The m-bed only needs 1 ton of ac. (1 ton is the amount of heat it takes to melt one ton of ice in 24 hours. For AC, this is how much heat you must pump OUT of the room.) If you zone this, you will force 5 tons of ac air into a 1-ton space. Pressure-wise, bad for furnace, bad for duct. Energy-wise, a waste of 4 tons of ac and blower capacity. 2. When a t-stat in a hot zone calls for AC, and no others call, you have short, frequent cycles loaded with fast pressurized air. Dehumidification is reduced. Condensed water on indoor coil has little time to drain, and then is re-evaporated and sent back to the air, leading to mold problems. Best to have large zones or to have two or three small individual systems (furnaces and ac units) which are more easily balanced. With your 5-ton system, suggest placing one t-stat (one zone) on each floor, regardless of tall foyer, and control temperature disparities with manual dampers. The rest of the story: This can only work with certain houses, depending on the way the ductwork has been installed. If the ductwork is not right for such simple zoning modification, the ductwork may have to be reworked. This can be a huge undertaking. Often in such cases the contractor will walk away. Then your best bet is to try to install some manual dampers to restrict air flow to certain areas so that it will be increased to others.

I would suggest telling the builder to remove the cost of HVAC from the contract, that you will take charge of that aspect of the project and coordinate with him its installation. As for the ‘HVAC guy’ that told you, “1-well per ton, at 250ft/ton”, this would likely give you a VERY efficient geothermal system. It ‘sounds’ like more loop than what’s usually required but I don’t know your geology. This could be correct; it certainly sounds conservative which is OK in my book. Best efficiency with ‘Liquid-to-Air’ geothermal heat pumps (liquid in the ground loops) occurs when boreholes are drilled one-ton per borehole, separated by at least 15-feet, connected in parallel, headers installed WITHIN the mechanical room, WITH the ability to VISUALLY measure the flow in EACH borehole! This will give you the capability to easily and quickly monitor, troubleshoot and balance the entire ground heat exchanger loop network. Money saved at this level by not doing this properly and taking shortcuts might become a VERY expensive curse later on should problems arise. You will get this money back when you cash out, sell your home and have an inspection done - if they know what they’re looking at! A mechanical room should be built in the basement or the lowest level, preferably at the center of the house; an ERV is essential. The mechanical room must also contain an ‘AS Built Book’ that documents the complete design, specs, startup procedures and detailed startup measurements, as well as all the details and detailed location of the buried ground loops. You should also have a paper copy and digital copy of this document kept elsewhere in your home as well as at least one paper and one digital copy off site for safekeeping. Included detailed pics of EVERYTHING! This like having an electro-cardiogram of your heart done when you are well so that you have ‘baseline’ data to compare to as a reference when/if things go wrong and to also prove that they were ‘right’ at time of installation. It also affords you the ability to hire any knowledgeable tech to come on-site and quickly understand what’s going on. This is important if your installer goes out of business or if you have a falling out. It’s also vital for recouping the maximum value of your system at time of resale. Stay away from attics for mechanical systems! Find the right company to do the foam insulation; giving it the appropriate amount of time to cure and outgas and you should be fine. Check references and accreditations, this applies to the geothermal contractor and duct designer/installer as well. One-way to further ensure the right size geothermal unit(s) would be to install variable speed unit(s), both fan coil and compressor. That way there’s some ‘play’ in the system and increased efficiency as well. The geo units will self adjust to whatever duct system they’re hooked up to, within reason and throttle down if there is too much capacity while still giving you proper dehumidification. Too small a system and you’re out of luck without expensive, extensive mods. Look into zoning - properly designed, installed and controlled! The thing to ‘watch out for’ with ‘fully variable’ systems are flow centers or pumps, if you will, that are also variable speed, that they do NOT throttle down to a level where ‘turbulent flow’ in the ground loops changes to ‘laminar flow’. Without delivering a seminar on ‘flow’ in this forum, suffice it to say that you will need to have a discussion with your installer on ‘Reynolds Numbers’ and let them educated you and give you the seminar. If they seem clueless or flippant on this subject then you’re dealing with the wrong people that have not been properly trained. Copy & Paste: http://www.waterfurnace.com/literature/7series/BR2700AN.pdf IMPO SR Here is a link that might be useful: International Ground Source Heat Pump Association at Oklahoma State University

There are a lot of issues here and a properly done zoned system is not necessarily cheaper - there are a lot of variables. If you use a better staged system (which you would really have to do to make it acceptable), the efficiency would probably be higher. Think of it this way, $4000 per unit or $7000 for an efficient, staged larger unit. Maintenance is 50%. Advantage single unit. If you have NG, and the single unit is in the basement, it will likely be a 90%. If the second unit is in the attic, it will likely be a 80%. Advantage single unit. Conventional practice in the SE is 1 unit in basement/crawl and upstairs unit in attic. If you do a single unit, it would be in the basement. Advantage single unit (since the attic has far greater temp swings). The advantage here is on efficiency and life of the unit. Even the refrigerant runs are shorter to the basement - more efficient. Single unit outside - better use of outdoor space. Advantage single unit. I definitely don't think the answer is always 2 units are better than one. If you can be in the spec homes and try out their zoned system and it is acceptable to you (or unnoticeable), then why not? But you really want to find days that need HVAC a lot and there aren't that many in our future. But you could go and play with the stats and force it to run hard. You definitely should have stats on both floors.

They've also said that a system is working well even when its 20 degrees behind (set at 72, but 85 inside and 95 outside). I know you may need greater detail, but does anybody have any recommendations short of what my HVAC co recommends (replacement)? The house is a 2 story house, you're setting the upstairs unit high 85 inside then wanting it to drop to 72? So are you doing this with the down stairs unit as well? Remember heat rises, so that upstairs unit is under a much heavier load than the newer downstairs unit. (cooling falls, heat rises) The spaces are zoned... but there is a tandem going on because both these zones make up the structure. So if the upstairs is a 85 in the heat of the day 3-6pm in some cases 3-7pm / maybe 3-8pm under dire circumstances. It's going to take time depending on more than just a few variables. It could easily take 4-5 hours to pull down to desired temp... even more so if the downstairs unit is turned up or off. I service the Katy, Texas area.