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zootjeff 06-29-2009 02:44 AM

Duct work re-design for Heat Pump addition
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I'm putting in a heat pump and re-doing all the main stack duct-work. The base can that I had was rusting out and I need to add more supply to the upstairs.

Here is my old design:

Here it is after tear down on the first evening:

Here was the base can:

Here is without the base can ( I'm tempted to pour concrete in here and seal it off. I'd also like to put a vapor barrier between the new can and the concrete, there are lots of rust stains..

Here is the feeder base plenum, notice that one collar has fallen off and years ago I beefed it up with metal tape..

Here it is after cleaning it up a bit:

And here it is with the 2x6 header showing, more on this later:

Here is my proposed new design:


So now the details:

I'm putting in a 2.5 ton heat pump. I need to get the new base can because the old one was rusted out, you didn't see it in the pictures, but the dirt had opened up a big hole in it. I have a Trane XV90 Dual Stage variable speed fan 80,000 btu furnace. It rarely gets to the second stage when it runs so it is a little oversized for the 1800 sq/ft house.

The old base can had a 26.5 by 26.5 opening at the top. Out the bottom there was/is a 22 x 12 inch feeder duct to the supplies that go under my house. There are 3 12 inch round ducts coming off that.

Now my questions: my 22" by 12" going into the crawl space is 264 sq/in. Then it feeds 3 - 12" ducts at 113 sq/in each.

I'm trying to deside if I should replace the feeder can too. Obviously the collar is coming off and that annoys me, and the 22x12 doesn't connect well to my 17.5 wide new can. So I'm thinking of knocking out the 2x6 header in the last picture and going to a 17.5 by 13 feeder, and getting a new feeder can with better new collars going to the 12" ducts. I also plan to put dampers on all of them. Is it ok to knock out that 2x6? The foundation can support its self I would think..

The down flow furnace supply opening starts out 17.5 x 20 or 350 sq/in then it would go to my reduced 227 sq/in, Then to the three 113 sq/in ducts or 339 sq/in.

I'm also adding a supply for the upstairs. They had stolen a feed off a 12" line that was supplying 3 10'x10' bedrooms and sent it to the 400 square feet upstairs. I want to come off the side of the base can with something pretty beefie to the upstairs.. I'm thinking of 20x7 duct that goes up and eventually gets to a register in the room right above.

I am changing the way the return air comes in too, 10x18 for downstairs, 10x20 for upstairs so 380sq/in total on return air.. I'm going to put in a floor return because I want to use the space where the old return was to route the new supply to the upstairs room.

Does anyone have comments? I'd appreciate any comments or concerns you might have for me.



sktn77a 06-29-2009 03:39 PM

Well, the 2x6 header doesn't appear to be supporting the concrete above it (no end supports for the header) so it looks like just a nailer for the supply trunk. You seem to have thought this out quite carefully, but hopefully someone who knows what they are talking about (BeenThere?) can offer some advice.

zootjeff 07-04-2009 03:21 AM

Status update - ordered some material
59 Attachment(s)
I went ahead and ordered some material:

Here is what I'm out so far:

Here is what I'm building as of now:

Here is my drawing from which to order the plenums that I'm replacing:

So far only my coil set has arrived.

I've got all next week off. Monday and Tuesday the main shipments come.
Some time next week the Plenums will come..
Next step is to fill the pit with concrete so the plenum will have a flat surface. They had stuck a piece of wood right on the dirt to level the old stack. It had rotted out a bit, only a matter of time before the whole thing started sinking..

Then I'll place the pad, run the electrical, run the line set, start building the dampers and take-offs..


zootjeff 07-10-2009 12:26 AM

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I decided to concrete over the dirt pit where my previous plenum was.

I built some forms in the shape of the old can.

I built a screeting jig to skim along the top to make the slab level:

Here it is after the first pour:

Here is the slab after the forms removed:

And another view, I didn't overflow behind the forms to dress up the walls yet. I filled the form stake holes with sand as to provide a means to drain standing water if it doesn't make it out the hole into the crawlspace:

Then I put the forms back with on side removed for easy removal, put concrete back behind them and built up the forms on the tall voided side. After that setup for 3 hours, removed the forms from the second pour, then the next day went back to patch all the holes with grout:

One very sealed off concrete plenum stacking area:

You can also see the 2x6 headder popped out just fine. I cut it in half with a skill saw with fence set, then it popped right out..

zootjeff 07-10-2009 12:45 AM

59 Attachment(s)
My Condenser, TXV, Cased coil, and pad arrived via FexEx LiftGate:

Base Can and Coil seem to fit together:

Trunk and Dampers:

Top Transition fits nicely. The fabricator asked why I had the flanges at the bottom sides of the transition bent in rather then out. My last transition had them bent out too. I think that is standard so they can screw it down to the furnace. I like what I did here because it bought me 20 square inches of less restricted airflow at the base of the transition. I know, picky and anal and minor, but I'm glad I did it..

Yesterday I spent the day doing plumbing. I need to move the water heater over a little, so while I was at it I put in a cold water cutoff, re-located the backcheck valve for the sprinklers and put in PEX wirsbo 3/4 water lines. This way during the winter I can turn off all the outside sill-cocks with one valve without having to go into the crawl space:

AndrewF 07-10-2009 09:12 AM

Very nice install and write up. It looks like you thought this one through pretty good.

It is definitely a lot of work to DIY, but as long as one thinks it through, has an understanding of what needs to happen and implements it well, it will pay off in the end.

I did my own upgrade this past winter as well. Required new trunks, return drop down, box, etc. It was a 5 Ton system and took many hours of work to get it done.

Home Air Direct 07-10-2009 09:21 AM

Very nice pics and good job so far.

If there is ever a divorce, I bet I know who will fight for the furnace :jester:

zootjeff 07-12-2009 05:51 PM

Where to put the Suction and Liquid?
59 Attachment(s)
I'm going to close off the drywall next. I want to drill the hole for the 7/8 and 3/8 lineset. I could just use the hole a little further over where the plumbing is routing, but I'm not wild about the idea of weaving through the water heater stand. Does anyone see a problem doing it this way? That way it comes out and hugs the ductwork then 90s up at an angle and then 90s into the coil. What would you do if it were your house?

zootjeff 07-21-2009 04:19 AM

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Work on the drywall continues:

My DIY control method for the dampers that will be under the house. Basically I have a control line that will connect up to the dampers and be controllable for all 12" ducts off the main trunk. I'll mount them all on the side of the furnace for easy access. Much lower cost then the 80 bucks a pop for the electric, or the other methods of control.

Here is the twist lock control lever:

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