In the middle of an HVAC install, is return size right?

[visionik]

We have a Trane 16i 4 ton system that is currently being installed in our 60 year old cinderblock house in Orlando, Florida; along with new supply and return ducts.

The installer said that we should have 1 square foot of return for every ton. Plan was to install a 18x30 grill for the return, which he said up front was about 5-7% smaller than it should be. However, this comprimise was acceptable as our all cinder-block with solid pour and rebar everywhere house can be difficult to work with.

When I came home today I found that their is an 18x30 grill... however, they have about 1 foot of duct behind the grill and before the bottom of the air handler. Due to the way they installed it, that duct is 13x27 for that approximate 1 foot distance.

Won't that effectively make the size of the return 13x27, or 351 square inches for a 4 ton unit? That sounds way too small. Am I wrong?

[RoBoTeq]

The contractor has not taken into consideration the resistance of the filter. Filter grills must be larger then open grilles with filters at the opening to the blower compartment.

[t527ed]

the whole return duct is only 1' long? that baby will roar!

[billva]

4 tons?

how many cinderblocks in this home?

give a better idea of home size, location and efficiency.

[visionik]

Robo - there isn't a filter in the grill itself if that is what you meant, it goes like this:

- grill in the wall

- 1 foot or so of 13x27 duct

- insulated platform box underneath the air handler

- at the top of the insulated platform box, a 5" trane perfectFit media filter between the box and the air handler

I know that the return is going to be louder, will it literally be a roar?

This house is difficult to work in. Their was one owner before us, he designed the house himself and had it build in 1948. It's cinderblock and rebar everywhere - halways, closets, etc. Half the house has a flat roof, half a scuttle type attic. Roof is 1.5 inch thick tile.

Eye of the worst hurricane passed right over our part of downtown Orlando last year and we didn't even have to replace a tile. Unfortunately, the house resists contractors as well as it resists hurricanes.

The old hvac system used an underground return system. Basically about a 1 foot diameter metal pipe that was set down and then the foundation poured over / around it. It went to a return across the hallway from the air handler and then to another point across the house to near the kitchen.

I've been told the underground pipe was probably originally for heating.

The primary reason we're doing this new system is allergies. In addition to the 5" media filter, we have a whole-house dehumidifier going in. I was also told by several people I got quotes from that the underground return should be closed off and new returns put in as it was probably in bad shape after almost 60 years - open in places, dirty - basically all stuff that's not good for allergies.
s
The company I hired suggested that it *not* be replaced.

However once they came out and took the air handler up, they could stick their head down in their and look around. They then said no, it was pretty bad, and suggested that we should consider new returns.

The problem is, all those solid pour walls and the flat ceiling make return install very difficult.

So after discussing options with them, we ended up with the plan I outlined above... but does that 13x27 duct section significantly reduce return air flow?

Thanks again!

-J

PS: The HVAC company owner is very straight-forward and has not been pushy or salesy at all. He has stopped by twice a day to review progress. He hasn't seen the duct behind the return yet. If it's wrong I'm sure he'll agree it should be bigger, but I wanted to hear what folks here thought first.

[visionik]

Billba -

House is about 1900 square feet.

In downtown Orlando on a Lake. About half of the rear of the house is big windows onto the Lake.

Built in 1946.

Cinderblock for every wall. And I mean every wall. Closets, hallways, everything.

We have very old windows that will be replaced right after the hvac system goes in.

All in all, I'd say the effeciency is "not great", but we're slowly improving it.

Prior unit was a 4 ton trane as well.

Air handler is variable speed, and we're also installing an Aprilaire 1700 dehumidifier.


[Edited by visionik on 12-16-2005 at 08:30 PM]

[t527ed]

for a run that short 13 x 27 should be plenty of air flow.
18 x 30 grill probably does not have that much free air opening.

insulated platform box and media filter may help quiet down some. sounds like the way house is built you just gotta do what you can.

[Edited by t527ed on 12-16-2005 at 08:31 PM]

[billva]

has anyone done a load calc. with the improvements involved?

new windows will significantly reduce the load (radiant and infiltration)thereby short cycling your 4 ton a/c which will create a MORE humid enviroment, which will in turn cause your dehumidifier to work more.

why not size properly for the best of both comfort and efficiency.

[dash]

The 13X27 is fine,the 18X30 grille is too small and will likely be the source of noise.Test this by temporarily removing it after everything is running.

If that reduces the noise,see if the size can be increased or ask for a less restrictive grille,a commercial style grille with wider spacing then commonly used for residential in your area (we are 70 miles west in Crystal River)will make less noise.


Also ask that the variable speed be set for 350 cfms per ton ,for better dehumidification and less air noise.


Before they install the outdoor unit,consider a two stage compressor,so the possible oversizing due to improvements will be largely negated.


Good luck!!!

[visionik]

Billva -

Owner did a load calc, I believe using Manual J

Billva and Dash -

As I understand it, the outside unit for a Trane XL16i is a two-stage scroll compressor, and the two stage capability will help with the load change from how things are now to where we should end up.

Does that make sense?

Dash -

Thank you very much for the tips on the grill and on setting the air handler for 350 cfms per ton. I've been to Crystal River... home of one of Florida's two nuclear power plants!

-J

[Edited by visionik on 12-16-2005 at 09:35 PM]

[billva]

if you need 4 tons on the hottest day in orlando then yes, it makes sense.

if however the improved load only requires 3 tons, then you're screwed.

[RoBoTeq]

My eyes must be tired. I coulda swore I saw "filter" in front of grill....sorry.

[beenthere]

Originally posted by billva
if you need 4 tons on the hottest day in orlando then yes, it makes sense.

if however the improved load only requires 3 tons, then you're screwed.

With the addition of the dehunidifier he'll be ok if its over sized, considering its a 2 stage condensing unit.