How do I determine if I need a 3 ton or 4 ton air conditioner?

april_loveMarch 9, 2012

About 6 months ago I came to this forum and received some excellent information about HVAC systems.

I have two quotes and both vendors suggested the same furnace; The Infinity 96 Two-Stage Gas Furnace Model: 59TN6.

However, one vendor suggested a 4 ton Infinity 21 SEER air conditioner and the other vendor suggested a 3 ton 16 SEER air conditioner.

How do I make the determination on if I need a 3 ton or 4 ton system? I'm in Michigan and the air conditioner is primarily used during the summer months. My air conditioning bill typically peaks in July only.

The vendor that recommended the 3 ton system did take measurements of the house. I'm not sure if the other vendor did. Also, I currently have a 4 ton air conditioning unit which is probably the original. The home was built in 1967.

Please help. Thanks.

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CJ Mechanical of North jersey llc.

A manual J load calculation is the only real way. This requires measureing windows and type, insulation,infiltration,ectt. Ask them to perform a FULL manual J and to provide a copy for you. explain to them that in this day and age you want the most efficient system and need to know what the heat gains are in the house. Rule of thumb or simply replace what you have is not advised with out the manual J

    Bookmark   March 9, 2012 at 7:06PM
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fsq4cw

Have you discussed the merits of a heat pump?
SR

    Bookmark   March 9, 2012 at 8:29PM
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april_love

All of the vendors I spoke with stated that a heat pump wasn't a good option here in Michigan.

    Bookmark   March 9, 2012 at 10:39PM
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fsq4cw

Did they explain why? What's your electrical rate per kWh? What's the gas rate?

SR

    Bookmark   March 10, 2012 at 12:30AM
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mike_home

Hi April,

In your past posts you stated the house has 2400 sq. ft. It is difficult for anyone on this forum to state what is the correct size for your air conditioner. The load calculation is the only way to do this properly. I would have much more faith in the contractor who took detailed measurements. It is likely the cooling load somewhere between 3 and 4 tons. One contractor may be rounding up, and the other down. The 2-stage Infinity AC would be a good choice. On the low stage it would be operating around 2.8 tons. You would be comfortable and do a great job of removing humidity.

How many days a year does the temperature go above 90 degrees in the summer? I personally think a 21 SEER system is overkill for your part of the country. It is unlikely you will ever see a pay back of the additional cost over the 16 SEER unit.

    Bookmark   March 10, 2012 at 9:18AM
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brickeyee

"Did they explain why?"

Physics limits the efficiency of heat pumps in very cold areas.

Frost formation on the outside coil starts hitting efficiency badly, ad there is simply not a lot of heat to easily extract at lower temperatures.

    Bookmark   March 10, 2012 at 3:04PM
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fsq4cw

Re: brickeyee

While what you say is true, I live in Montreal where MANY have heat pumps and use them down to at least 10F. So depending on the electrical rate, it may still be a useful option.

SR

    Bookmark   March 10, 2012 at 4:11PM
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brickeyee

"So depending on the electrical rate, it may still be a useful option. "

And the winter humidity level.

And how long you expect the system to last.

    Bookmark   March 13, 2012 at 3:25PM
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