countryboy

I assume your home will have very good new home construction and insulation qualities.

have you received the load calculation in writing on the software letterhead and reviewed it carefully room by room? Is home sgl story or two story? will the home have zoning controls?

what is total BTU heat gain and heat loss and at what design temps for both cooling and heating?

what are the cooling BTUs and heating BTUs for both the 4 ton and 5 ton ClimateMaster GHP systems?

I am no GHP expert but I don't understand the logic or the statements of the dealer recommending the five ton system. I have to admit I am even surprised at the need for a four ton system.

show me the numbers first.

post back.

IMO

Re: countryboy

Further to tigerdunes comments, which I agree with, I would want to know where youÂre located, heating & cooling design temperatures for geothermal  and ALL the details of a proposed ground heat exchanger and desuperheater design & hookup.

That extra ton of capacity may be important particularly if youÂre located in a heating dominated location and installing a desuperheater, as some of the heat that would otherwise go into the house will be going into the domestic hot water. This could be a factor on some of the coldest winter days.

Variable speed (ECM) blower with a 2-speed compressor in a 5-ton unit may give you the added comfort and peace of mind youÂre looking for if max efficiency is your goal. If 4-ton is enough for cooling and you donÂt mind that you may use the backup a little more often, you can go with the smaller 4-ton unit.

Proper heat gain/loss calcs, duct sizing for CFM, and design of GHX are crucial for optimum comfort, performance and efficiency.

SR

Just to add my $.02 - if it is a heating dominated climate - the upcharge seems reasonable and can prevent backup from running to recoup the money. The airflow argument is spurious.

But to make an informed decision, the facts of your HDD and CDD and manual J numbers are needed.

based on username, this looks like an Oklahoma locale....

Sorry to leave you guys hanging.... I have been pouring the footing and forming for my floor the last couple of days. I will post my heat load information shortly.

Thanks,

See the following link. Hopefully this gives you what you were asking for. As a side note, I called the local Climatemaster distributor (as requested by Climatemaster), and they agreed that I would see better comfort levels with the 5 ton unit and suggested I go that route. They also stated that the cost increase for the 5 ton unit was very attractive, and that the contractor was not trying to "upsell" me on anything since the price was so low.

Anyway, let me know what you guys think. Thanks again for the advice.

Here is a link that might be useful: Heat Load Calc

I'm not a pro, but a couple of things popped out at me. The floor heat load seems high, while there is zero floor cooling load. That doesn't seem right. What type of foundation do you have?

The ventilation load seems high, too.

I don't understand the airflow of less than 1200 CFM. It is generally accepted that you need 400 CFM per ton of capacity. A four ton system should be moving 1,600 CFM of air. It should at least be sized for that much.

FWIW, we have a new (tight) 2200 SF ranch over a walkout basement with a two speed four ton system with a VS blower. It is more than adequate, and our temps aren't all that different than OKC.

I suggest buying HVAC-Calc and running your own load analysis. It's worth the relatively low price.

Here is a link that might be useful: HVAC-Calc

Forget what I wrote about the airflow above. I was thinking about one thing while writing about another. It doesn't apply to the Manual J results.

I'll go have more coffee now.

I didn't totally understand the airflow shown on the output either. Surely 1200cfm is too little.

As for the floor cooling, all I can guess is that the floor temps around here are pretty mild, probably around 60-65 degrees year round, so no real cooling is necessary and in fact the concrete floors probably help cool the house some. Heating, however, is a different story. Concrete floors in the winter are very cold even here in Oklahoma. I will have some radiant floor heating in the master bath, but I don't think it is enough to affect the heating requirements of the unit.

Everyone I talk to is telling me that the heating requirements are what dictate the size of the unit, not the cooling requirements. I like the idea of not running the backup, and on geothermal units I've been told that these backup heat strips are truly emergency only. Geo units do in this area do not need the backup units for daily operation down to around 5 degrees (which is very uncommon here) and they are only needed if the unit goes out. That is an advantage of going to the larger unit.

The main question was about the airflow requirements of a 2700 square foot house. Is there not a general rule of thumb for CFM per square foot?

Thanks,

400 CFM per ton of AC, not per sf of house. A 5 ton unit would need really large ducts to move 2000 CFM. Bad ductwork is a real problem in the HVAC industry. I would check your bidders out very carefully, and ask for detailed ductwork information.

It sounds like you are on a slab. Is there insulation under the slab, at least at the perimeter?