Converting a home with one AC unit to a dual zone????

[BBatesokc]

Recent talk about dryers and such in another thread got me to thinking about a project I'm considering undertaking at some point and wondered if anyone here had any experience with this and could provide insights, recommendations, cautions, etc.....

The home we moved into is a two-story, built in 1965. Its on a single heat/air zone (is that the right term?). We will rarely ever go upstairs (two huge bedrooms) unless we have overnight guests. I hate the thought of heating and cooling that space (guessing it to be about 700 square feet) when we won't use it - and when we do, there will still be a noticeable temperature difference.

How realistic is it to separate the two floors into two different zones? I assume all the duct work will have to be removed and redone. Also, the bottom floor is a cement foundation with floor vents. The house has two returns on the bottom floor.

Is there any other option than ripping all the duct work out and buying an additional heat and air unit and then re-ducting all of it? Will I ever re-coup my cost?

Right now we just have the vents upstairs turned off (or as 'off' as they can be turned at the vents themselves). But, I've been told that is very inefficient as the hot and cold air hits those 'dead ends.'

I read online somewhere where some people have had a damper put in the the duct work itself to prevent the air from even being pushed into the upper floors of their house until they need it. Is this an option?

Or, what about those low profile European style AC units that are very slim and have a single box (usually up near the ceiling). We just returned from Belize and the house we stayed in had those in each room and they worked almost too well. But I hear they are crazy expensive.

Thoughts?

[DoctorTaco]

I am looking at buying a two story house that has upstairs/downstairs dual zoned heat and air. The owners accomplished this by having two exact duplicate systems. One furnace/blower in the basement/crawl space which feeds the first floor through floor vents. One exact replica furnace/blower in the attic feeding the second floor through ceiling vents. Outside there are two seperate AC Condenser units, one for upstairs, one for down.

Seems like a damned epensive way to set it up, but it seems to work well and probably saves a ton of energy versus heating the entire house when you don't need it done.

[BBatesokc]

I am looking at buying a two story house that has upstairs/downstairs dual zoned heat and air. The owners accomplished this by having two exact duplicate systems. One furnace/blower in the basement/crawl space which feeds the first floor through floor vents. One exact replica furnace/blower in the attic feeding the second floor through ceiling vents. Outside there are two seperate AC Condenser units, one for upstairs, one for down.

Seems like a damned epensive way to set it up, but it seems to work well and probably saves a ton of energy versus heating the entire house when you don't need it done.

I haven't priced it, but yeah, I'm assuming its an expensive endeavor. Probably best done during initial construction. My parents are moving back from Austin and are closing on a brand new home in Edmond and it has a 600 square foot 'bonus room' as the only room upstairs and its on its own heat and air. I thought it was a bit of overkill, but nice nonetheless.

[okc_bel_air]

You can look at installing eletric dampers in the existing ducts. Then a seperate thermosat upstairs can open and close the dampers depending on the temperature upstairs. We are doing this with a bonus room in our house now. We had a sufficient size furnance and ran new ducts to the new room and installed dampers. Still not cheap, but alot cheaper than installing a complete system.

[stick47]

You could get a multi zone spit mini system with heat pump for the upstairs. I have one in my shop. It's a single zone 12K BTUs.
No vents to run & super quiet.
Ductless Mini Split Air Conditioner AC Heat Pump 18000 BTU Dual Zone A C Heater | eBay

[LakeEffect]

We just put in a brand new system with four zones and ONE furnace/ac unit. Each zone has a master damper and then smaller dampers at the end of the duct run. Now, we had walls torn out, attic and basement access, so it was pretty easy for our guy to do, but I'd imagine he could do similar for you without too much work.

[Wambo36]

Are you able to close off the upstairs when it's not being used? I mean, is there a door either at the top or bottom of the stairs?

[BBatesokc]

Are you able to close off the upstairs when it's not being used? I mean, is there a door either at the top or bottom of the stairs?

No door at either end of the staircase, but each of the two bedrooms at the top of the stairs do have a door. We keep those closed and close the individual ceiling vents in each of those rooms. However, those vents never truly close 100% (and even occasionally 'whistle') and I've been told that simply closing the vent in specific rooms is not a very good solution and can be very inefficient by backing up the air flow within the ducts (don't know if that's true, but it sounded reasonable).

[Bill Robertson]

Since the downstairs is in-floor duct and the upstairs isn't there must be a plenum somewhere, my guess would be right at the furnace, with one main duct coming off of it to the upstairs. It should be pretty easily accessible and a damper could be installed in the main going to the upstairs at that point.

[BBatesokc]

Since the downstairs is in-floor duct and the upstairs isn't there must be a plenum somewhere, my guess would be right at the furnace, with one main duct coming off of it to the upstairs. It should be pretty easily accessible and a damper could be installed in the main going to the upstairs at that point.

That's sorta what I assumed. I really need to go look at the duct work. Its a walk-in attic, so its easily accessible. Looks to have been designed so it could easily be converted into a finished room (lots of room and high ceilings - nothing like my old attic).

[T-rex]

mitsubishi <sp> used to have a system called Mr slim or slimline
it had a small outside unit that controlled up to 2 separate inside units, you could probably get 2 units installed in place of one conventional a/c-heat pump unit to divide the house into 4 separate zones

[Rover]

mitsubishi <sp> used to have a system called Mr slim or slimline
it had a small outside unit that controlled up to 2 separate inside units, you could probably get 2 units installed in place of one conventional a/c-heat pump unit to divide the house into 4 separate zones

These type units are called multi-splits and are available from Mitsubishi, Daiken and a number of others.

[Servicetech571]

If your house has the typical slab ductwork with a downflow unit located in the garage, good luck. Most have a 20' duct coming off the downflow unit to the attic of the 2nd story and by time the air gets up there there's no pressure left. Close it off and have the downflow unit serve the downstairs. Add a 2nd system for upstairs, a minisplit is probably the most cost effective solution if you are primarily cooling one room. If there are multiple rooms install a small central system. For an upstairs area that's rarely used a 1.5 ton AC with 5KW of electric heat could be a cost effective system. Electric heat does cost about 3x the cost to run as gas heat, but installation costs will be $1,500 less than a gas furnace. Remeber you would have to run a gas line and install flue for a gas furance, not to mention the cost of the furnace. The question becomes how much electricity can you buy for $1,500 to run the heat strips in the winter. If the heat upstairs is rarely used, it could be quite a few years to make up the cost difference. You could also split the differnce and pay an extra $750 to have a heat pump installed upstairs instead of just heat strips, cost to run a heat pump is about 50% more than gas.