Advice on HVAC system

[skippy76]

I'm after some advice based on a future project I have. I have a friend who works in HVAC who will do my install, so, yes I will be consulting an expert. But as the inquizative person that I am I would like to have done all the research before moving forward.

My current situation

I currenlty have a second floor condo that is part of a two family property. The condo is about 1,100 sq feet (2 beds, 1 bath, 1 kitchen, 1 dining room, 1 family room). The current heating system is steam with the boiler located in the Basement. The boiler runs on Natural Gas.

We own the attic space and are going to be building an additional floor which will add an extra 850 sq feet. During this addition I plan on putting in a new HVAC system and remove the steam heating.

Requireements

I had a few thoughts as to what I would like but have been trying to compare the options without being able to determin which is best.

My requirements are:


heat to be provided by Natural Gas
Provide cooling and heating to both the existing 2nd floor and the new 3rd floor
Blower unit cannot be in the basement, it must be located within the new addition.
Second floor and new (third) floor must be contralable with different thermostats.


My thoughts


Two seperate blower units, each with their own furnace. Also, each would have their own condensor.
Single blower with hydro air. This would mean that the blower unit would be in the new adision but the boiler could be added to the basement.


So what other options do I have? Would it be beneficial to have two blower units, 1 per floor or is that overkill and not needed?

Am I better off leveraging a furnace along side the blower unit or is a boiler with hydro air more efficient? (space for either of them is not an issue).

Are there other options that I can consider?

Thanks for any advice,

Andrew

[beenthere]

2 gas furnaces with A/C.

Or 1 gas furnace with A/C, and zone it.

[skippy76]

Thanks for the response.

I'm assuming that if I go with two seperate furnaces I would need two seperate condensors.

Also, what are the key differences / benefits over having 2 seperate furnaces vs. zoning it?

[beenthere]

Redundancy. If one goes down at 2 in the morning, you still have heat or cooling.
When its 10 degrees outside, and every company is swamped and can't get to you for several hours, or a couple days, this is a big plus.

You don't run a 3 ton system to do a 1.5 ton load.

Can be cheaper to operate.

[skippy76]

Excellent, ok, sounds good to me. So I would go with two seperate systems, 1 for the existing floor and one for the new addision. If I wanted to be able to control individual rooms, would I setup each system to be multizoned? I presume this uses dampers. How effective is the zoning as I imagine that you only have one thermostat for the whole system E.g. is zoning of the ducts really worth it?

[dash]

Redundancy is the advantage,but at a cost.

Will likely cost the same as a zoned system,but not if you plan to add zoning to each system.

Two systems to maintain,and replace sometime,is more costly.

Most of all look at the space required for two systems.

[skippy76]

With regards to zoned systems, I'm kind of big into home automation. I currently have an INSTEON thermostat so I can control the temperature programatically through my home PC, as well as remotly. Are there any zone controllers that can be controlled via PC or does each zone just have it's own thermostat?

[larobj63]

Excellent, ok, sounds good to me. So I would go with two seperate systems, 1 for the existing floor and one for the new addision. If I wanted to be able to control individual rooms, would I setup each system to be multizoned? I presume this uses dampers. How effective is the zoning as I imagine that you only have one thermostat for the whole system E.g. is zoning of the ducts really worth it?

You're getting beyond the scope of what 99.9% of residential furnaces/air handlers do. Single zone will work very well if good airflow is maintained by a quality duct installation and the initial balancing is appropriate.

This is not to say you can't have zoning, it just ups the cost exponentially, and for little benifit, in my opinion - especially considering how small these units are.

I agree, two different gas furnaces, with associated DX cooling (two seperate condensing units mated with two evaps on the furnaces).

[skippy76]

Ok, thanks to you all for your excellent advice. So I think I'm going to go with two seperatre systems but without leveraging zones. I will probably continue to use my Insteon thermostats as I will still have the remote control of my house temperature / humidity.