Room air conditioner + ducting: a good idea?

OK - this may be a silly idea - feel free to laugh at me...
I have a 2nd story bed/bath suite that is currently heated with an electric furnace in the attic. Both the bath and bedroom are served by this unit.
I want to replace the electric furnace with something that is more efficient and can provide some cooling. An regular heat pump won't work because they don't make them small enough (1.5 ton would be extreme overkill for 350 sq ft). A mini-split system would be very expensive professionally installed.
There isn't a good place to install a room heat pump in an external wall.
What I would like to do is to install a room heat pump in an attic wall and rig up something to hook the output into the existing ducting. I will then set up an external thermostat to controll the AC power - this means I wil have to set it to heat in the summer and cool in the winter, but that is not a big deal. I will also have to rig up the return from the existing return. This seems like it would be an inexpensive and effective solution.
Does this seem like it would work?
Thanks! -Alex
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the manual calculation you did on the room told you that 1.5 tons is to big? Heat rises and I have seen allot of upper units undersized because the calculation was not done.
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What is 'allot' ?
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First you talk about efficiency, then you go on to cobble up some mess that may, or may not work at all! the two generally do not go hand in hand! Sorry, but I am from the school that if you want it done, do it right. Cut corners, try to re-engineer something and it never works as well as planned.
I don't recommend it, but you can buy most any equipment over the 'net and do at least part of the install your self. You may be able to find a local AC tech that may do the final connections and pump down for the line sets. The problem here is often manufacturers will not warranty their equipment that is installed by a homeowner. Greg
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Thanks for the observations Greg - that is insightfull. If I were looking to buy a house with a setup like I described I would probably think it was pretty lame, which is probably a pretty good indicator.
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Not pretty, but they DO make window heatpump units. Try Lowe's, Home Depot, or even WalMart.....

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I've been considering options for a bonus room over a garage (the only upstairs portion of the house) that I don't want to put on the central system.
I've done some research on "portable AC and Heat Pumps" that are not window units but stand alone units that generally require only a vent duct to get rid of the heat. They can be placed anywhere in a room that is adjacent to an area that can accept the vent pipe. They are more expensive than a window airconditioner/heat pump but still affordable at $500-1000 depending on the BTU rating. They use the produced water as additional cooling for the unit. Have seen units up to 13,500 BTU that can alledgedly cool/heat up to 450 ft.
I've not used one, only done the research. Maybe someone who has can give a review.
Do a google search for portable air conditioning and several manufacturers will come up.
Frank On 1 Oct 2005 14:49:16 -0700, snipped-for-privacy@logic-tools.com wrote:

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My father's upstairs in Myrtle Beach, SC is 300 SQ. FT.. Load calculation is just over 1/2 ton. We installed 9 SEER 1.0 ton Heil Heat Pump, 10 years ago. Trane makes a 1 ton 10 SEER now. I would use that. Yes, for 350 Sq Ft in your area, 1.5 ton seems awfully big, but it depends on insulation and glass as much as weather. A mini split would be a good idea if you leave the bathroom door open when not using it. Look at how many hotel rooms have a PTAC under the window in the main room and nothing in the bathroom that do just fine that way. Mini splits go down to 3/4 ton. Carrier makes one that is less expensive than imported Japanese jobs.
Stretch
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