Basic Home HVAC Design

[MGM]

What is the rule of thumb for calculating the cooling and heating load for a home -- with and without zone heating/cooling?

What are the pros and cons of oversizing a unit -- within reason?

Thanx--

MGM

 

[UtilityLouie]

Well, I wouldn't necessarily recommend "rule of thumb" sizing anything! Every house is different and exposures, amount of glass, shade trees on the property and home layout all have a great effect on the size of the furnace and/or AC unit. I have seen cooling loads on houses run from 400 to 800 sq.ft. per ton of AC. That is a pretty big range.

I would recommend, to get you in the ball park, a very basic heat loss/gain calculation. I do not know of any on the web, but I know that the WI state code has a basic form that they require where it leads you through the calculation process. It basically requires square footages and "R" values.

Be wary of any contractor that supplies equipment without a detailed heat loss/gain contractor. Your equipment could not only be oversized, which results in unit cycling (more maintenance) and an increased energy costs (start up current vs. running current). Oversizing also results in large temperature swings in the house which can be uncomfortable. The unit he could provide could also be undersized! Undersized equipment would work 85% of the time except when it is really hot or cold outside.

We just replaced our boiler last winter and three different contractors came in, but only one did an accurate heat loss calculation. This contractor was also the low price contractor with the best equipment for the price so it is not always a price issue.

Hope this helps.

 

[blmcghee]

try this site, might help some.

http://www.heatinghelp.com/