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Old 10-06-2016, 10:33 AM
 
153 posts, read 161,993 times
Reputation: 76

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I know I am going to get some flack here for this one, and people are going to say get a professional to test it, check your CFM, heat loss, return vents, blah blah.

We have a 500 square foot bonus room that was previously a garage, thus no heating or cooling was routed to it. Fast forward a couple decades and that garage is now the bonus room, with no floor above it (ie attic space). Sheet rock is down in this room so now is the time to route the HVAC.

The main supply duct (roughly 18"x8" square) is routed on the first story ceiling (of a 2 story house) via a drop down and dead ends at one of the walls to this bonus room. Which makes it very convenient to just tap into for this bonus room remodel. There is only 1 return vent in the whole house and it is NOT POSSIBLE to extend it to anywhere else in the house without doing some SERIOUS remodeling.

Question is do I need more then 1 register? I had a professional come out and say "they" would put two in on each side of the room, but this would require a drop down box in the bonus room to get it up and into the ceiling, since it is a drop down in the previous room. The wife does not want the drop down and it would cost around $1200 for this option.

Now what I would like to do is just throw a large 14"x8" register (or the largest size I can fit) on the end of the duct run that dead ends to this bonus room wall and be done with it. This option would be less than $100 and quick and easy. The large register would equal two normally sized ones that would be on either side of the room, and you have the main duct run to deliver the supply, vs running smaller 4" lines.

Now, in the winter months if we keep the door closed to this room it becomes an "ice box". If we keep the door open it is just cold, but livable.

Need to make an executive decision here. If someone thinks this is a BIG no-no please weigh in. I can always go to the $1200 option later, but would at least like to try my option first. I know it's not ideal, but if it gets the job done that is all I care about.

Thank you.
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Old 10-06-2016, 10:52 AM
 
Location: Johns Creek, GA
12,498 posts, read 48,489,653 times
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It sounds to like you've already made your mind up- do it cheap and be done.

The reason it's an icebox probably has something to do with no drywall ceiling(?) and I'll assume no insulation(?); and as a general rule the walls of a garage are not insulated either. So, pumping cool or warm air into the space is like opening the front and back while the HVAC is running.

Your current system was sized for the "conditioned space" of the home- keep it that way. Spend a little extra and get a heat pump window unit that will heat/cool that space. And it doesn't have to go in a window- you could set it up to be thru-the-wall.
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Old 10-06-2016, 10:53 AM
 
2,645 posts, read 1,524,738 times
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I'd give it a shot and then call in someone else later. But is the reno permitted? If so they may dictate what's required for it to pass the inspection.
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Old 10-06-2016, 11:03 AM
 
153 posts, read 161,993 times
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Yes the renovated garage was done decades ago, and has been fully finished for that length of time as well. This is a remodel to the room, in which WE tore down the drywall. So there is already insulation, etc etc in the room.

And when I say it was an ice box, that was with all the drywall and ceiling up in it's original state, not with all the drywall down. Our remodel consisted of tearing down the drywall for several reasons that I could right a couple pages on here.

However, we did get a new air handler and heatpump sized for the whole house, including this room, last year. So a standalone unit shouldn't be needed if we can route the HVAC in the room now.

If anyone else has opinions, please post.
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Old 10-06-2016, 11:15 AM
 
4,956 posts, read 2,239,216 times
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How about a split system for this one large room only? No need to get involved with the rest of the house's duct work, plus you can control it separately. Just needs a hole through the wall big enough for the two refrigerant lines.

If you add to the existing duct work you will need to put the outlet at the far end of the room from the door where you expect the return air to be sucked from. Otherwise you'll air condition the 4 feet in front of the door and not the whole room.
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Old 10-06-2016, 12:28 PM
 
153 posts, read 161,993 times
Reputation: 76
We got a quote for a split system, $2500 for a heat pump setup. Unless I am way off for this, it too much, and it is MUCH MUCH more convenient to control temps with one system. If we could get a heat pump standalone system in place for under $500-750 range I would consider it.

That you for the input. Anyone else who has insight please post! This is good so far, thank you.
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Old 10-06-2016, 04:48 PM
 
605 posts, read 671,357 times
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Your best chance to pull off 1 supply would be to position it as far away from the return path (doorway) as possible. Conventionally, supplies are near glass or point towards the glass as that's usually the most efficient heat loss occurs. You just want the warm air to sweep across the room.

As for the blah, blah, blah, your biggest problem is that you'll be robbing peter to pay paul as an 8 x 18 is good for about 600 cfm, and if it's a lined duct, only about 400 cfm. Your new room needs about 400 cfm but what about the rooms where that air from that trunk used to go? What's left for them from your 400-600 cfm trunk "budget"? I hope there's more to the story that you're not mentioning.

Forget about the $1200 option...that's for suckers. Save and double that for a proper solution...a minisplit.
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Old 10-06-2016, 06:17 PM
 
153 posts, read 161,993 times
Reputation: 76
Thanks for the reply btuhack.

As for air budget. That 8x18 duct is supplying half the house, which would equal roughly 1,300 sf. There is another 8x18 duct that runs the other direction and feeds the other 1,300 square feet of the house.

This bonus room that I am mentioning is at the end of the house. So all the other registers from the main trunk feed off prior to the bonus room. Also, the bonus room is right near the door, which is not on the other side of the room.
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Old 10-07-2016, 08:35 AM
 
4,956 posts, read 2,239,216 times
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Quote:
Originally Posted by COD1628 View Post
...MUCH MUCH more convenient to control temps with one system...
I'm not an HVAC expert, but I would suggest that you may get much better control of temperature in your large room with a separate system locally controlled than trying to control it with a single whole-house system driven from a thermostat remotely located. I would be worried that the room in question being at the end of the duct and with possibly doubtful air return, may always be the hottest in the summer and the coldest in the winter.

The bigger the space you're trying to control with a single control, the greater the variation over the space, and the wider the temperature swings in the areas far from the thermostat.
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Old 10-07-2016, 09:49 AM
 
6,040 posts, read 4,404,099 times
Reputation: 16753
I hope that while the room is torn up for remodel you insulate the heck out of it, including above the ceiling?
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