HVAC Sizing

When getting a new HVAC installed, how do you know you are getting the correct size for your home?
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Run a heat load on the house. There isn't a 'rule of thumb' that works.
There are a bunch of programs available on the internet.
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Indeed. lets look at how long its taken bill gates to write a program that isnt full of bugs and doesnt crash.
Ok now suppose we have a rock solid, building-code-approved load calculation program. 10 different people, inputting data independently, will arrive at 10 different 'answers'. Which one is most correct???
OK now we have the exact btu gain/loss numbers, and now we must select pieces of equipment that most closely matches the heat gain/loss numbers, and still stay within the customers budget.....
Guess what?? NOBODY makes a 29,000 btu gas furnace with a 57,295 btu, 5 ton blower, which is exactly what the load calc says is needed..........so now what? Oversize the heating to obtain the desired cooling airflow??
A tiny fact that most consumers are never made aware of is that a heating or cooling load calc is accurate at only one point in time, and that is when indoor and outdoor ambient temps are at DESIGN conditions. Any other time its either oversized or undersized.
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Take the highest, and lowest and trash them... the rest should be pretty close.... go with the averages.

For the most part this is true.... there are also a lot of financing options avalable.

This is going to to be dependant on the region, and the design perameters.

There are multi-stage furnaces, and air conditioners available.
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Noon-Air wrote:

How does HVAC size effect its energy efficiency? The region is Washington DC
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Different topographies determine different sizing.

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snipped-for-privacy@gonefishin.net wrote:

Oversizing will cause the system to short cycle therefore the humidity will not be reduced enough, unless you cool to a very low temperature and it will then feel cold and clammy. Washington DC, Wash. Natl. AP, Winter Design 99% at 14-F; 97.7% at 17-F. Summer Design, at Wash. Natl. AP is 91-F Dry Bulb, 74-F Wet Bulb, or around 44% relative humidity. With that humidity level, a 13 or 14-SEER with a Scroll compressor and a TXV refrigerant control should work okay with a fairly high airflow.

Right-on - gofish. In your cited case; I would go with a separate air handler for the long season for cooling. Heating would probably be a short season, therefore you might be able to go to electrical baseboard heat or some other option.

Do everything possible to bring that heatload down as low as possible, then size the equipment accordingly. That one time investment will save initial costs and utility costs over the life of the equipment. - udarrell - Darrell
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Air Conditioning\'s Affordable Path to the "Human Comfort Zone Goal"
http://www.udarrell.com/air-conditioning-total-heat-enthalpy-latent-heat.html
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On 11 Jul 2006 04:27:11 -0700, walter snipped-for-privacy@my-deja.com wrote:

Add up the door knobs in your home (Ex. 21 knobs) Divide that number by 7 (21/7=3) 3 = 3 tons of cooling. "Thumbs Rule" Bubba
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