block load versus room by room

[heetseeker]

I read somewhere that said that equipment selection is based on a block load which I assume is a square foot method plus insulation plus window size, design temp etc. They said a room by room manual J is for duct design. Is this true? That would mean that most people when replacing their system would need a block load.

[Gunnery Sergeant Hartman]

A block load is not a square ft. method.

It is just the room by room, but without the rooms.

Basically just one big room.

The only correst way is the room by room.

[Irishmist]

As you indicated, the room by room is a good way to cross check the block load. Whenever I layout a new system, I always do a room by room so that I know what the air distribution should be. For example, if I have a 3 ton system and the cfm for the total system is 1200 cfm, then I would do the room by room to indicate how much cfm I need to each area of the home. Good question, and good answers.

[swat]

Room to room is the only way to go. A whole house is good for a ball park figure but which room gets how much ac or heat is guess work if you just do a block. It is like saying your house needs electricity and we want to run X number of appliances and other items but we arent going to tell you which room it will go in. Just guess at it. Well you know they arent going to have certain things in certain rooms so you have to guess which circuits are going to which areas so you dont under or over size the breakers to that room.

Good luck

[heetseeker]

Thanks for the replies. Sorry for being dense but it seems that there is agreement that room to room is the best so you can determine the cfm required by each room. Is a room to room Manual J needed for sizing equipment if no ductwork is planned?

[swat]

Basically the man j will determine the load. From there it is the contractor that recommends the equipment based on the load capacities of the availible lines of equipment. Then it is up to you and the contractor to select what you think is best or what would work for you and your home.