I have a one zone 2-pipe hot water heating only system. All baseboards are BaseRay cast iron from Burnham. The main line is 1” pipes and the branches are ½” pipes. I planned adding zones 2 yrs ago when I converted from oil to gas. So the Burnham alpine 105 gas boiler is big enough for planned additions.

Our 1950s’ house is a one floor Ranch style house with a full basement which has the same size and layout as the first floor. The size of the first floor is 1600sft. The basement is underground and only has less than 1’ above the ground.
There is a living room, family room, two bedrooms, a bath and kitchen on the first floor. The family room is an addition and is heated with electric heaters now.

Now I am planning to do two things:

1. Remove the electric heaters and add cast iron baseboards in the family room to use hot water heating;
2. Split the bedrooms out from the existing zone to create a separate zone and add a basement bedroom into the new zone.

A further plan is add the third zone to heat the basement after it is finished few months later.

Here is the layout of the existing system: http://www.flickr.com/photos/oldyoungguy88/6775074282/in/set-72157629065428756
And here is the my new plan or design: http://www.flickr.com/photos/oldyoungguy88/6921189821/in/set-72157629065428756/

I have done the heat loss with HeatLoss Explorer 2 and the results are the followings:
Zone 1:
(FamilyRoom) 15060 + (LivingRoom) 14030 = 29090 BTU/HR

Zone 2:
(Bedroom1) 5409 + (bedroom2) 5409 + (bedroom3) 2657 = 13475 BTU/HR

So I have figured out the family room needs about 30 ft CI baseboards. I have bought enough WeilMcLain CI baseboards for family room and basement.

I am trying to figure out the circulator size but have two questions to ask first:

1. The existing CI baseboard (BaseRay) has ¾” openings but the branch line is ½” size. I think that is why the existing baseboards are much longer than required length based on my heat loss number. The new WeilMcLain CI baseboards are the same as BaseRay with ¾” openings. Should I use ¾” branch line or use ½” branch line? If I use 3/4”, I am worrying about two different branch pipe sizes in one zone may cause uneven heating. I am fine to add little more baseboards to use ½” branch line. What you will do for this?
2. Do you think my above heat loss numbers make sense from your professional experience?

I will ask my circulator calculation questions later.

Thanks,

You don't have a two pipe system. You lost that when the end was connected. This should not have been done. The circulator must have a start and finish if you have two pipe. I am surprised you are not having problems heating with the layout you have.
Your new layout should work fine.
The extra baseboard was installed due to the fact the installing contractor probably did not do a heat loss. I would suggest the same amount of oversizing as the existing radiation for more even heating and utilizing lower water temps which will make the boiler more efficient. The lower water temp the higher the efficiency the higher the efficiency the lower the efficiency. You boiler will operate between 99% down to about 86% dependent on water temperature. The smaller the zones the lower the efficiency. Also, if you have a 105k boiler your boiler is only about 200% oversized....Sorry. The advantage is you can turn down the high side to save fuel as it will be a smaller boiler. The down side is you cannot lower the lower side so the boiler will be too large for smaller zones.
The pipe size to the radiation is sized on amount of heat required by the baseboard/room.
Use these numbers
1/2" pipe will carry 17,000 btu's
3/4" pipe will carry 40,000 btu's
1" pipe will carry 70,000 btu's. If the existing system is 1" pipe I would have to wonder why the boiler was not an ALP080.
Both the zones above each are less than the minimum turn down on the boiler where the ALP080 would have been 16k.
The more over sized the boiler the larger you want the zones to be or you may end up installing a buffer tank to avoid short cycling.

thank you sir.

It is not easy to find a real professional like you.

What's the buffer tank and how do I know my boiler is short cycling?

Short cycling is the boiler running too short of a cycle to keep the boiler efficient. A very minimum run time should be 10 minutes. A good run time is 20 minutes or more.
The Alpine has a screen that shows # cycles and hours of operation.
To determine average runtime use the following formula.
ART = (Hours of operation x 60)/Boiler cycles

For buffer tank info see the link below.
http://www.comfort-calc.net/Buffer_Tanks.html