H/VAC

[MCassady]

Hey everyone,

 

I'm looking for some guidance for the placement of an H/VAC system. The home has a walk-out basement on the back half of the house, but floor registers throughout the house aren't an option because the front half of the house will be built on a slab. In the current design, I have the system placed in the basement with a duct chase the leads to the attic. Are there any obvious flaws with this idea that I'm overlooking? I'd like to avoid "hot spots" on the far side of the house. Will distance between those rooms and the unit be an issue? If anybody has some input, I'd really appreciate it. Thanks. 

[Alaskan_Son]

I really think you're asking in the wrong place.  Completely depends on your climate, the home's construction, the lengths of the various runs, the sizing of the ducts, heating/cooling units specs, etc., etc.  This is a question for your mechanical contractor or mechanical engineer IMO.

[MCassady]

4 minutes ago, Alaskan_Son said:

I really think you're asking in the wrong place.  Completely depends on your climate, the home's construction, the lengths of the various runs, the sizing of the ducts, heating/cooling units specs, etc., etc.  This is a question for your mechanical contractor or mechanical engineer IMO.

Thank you.

[rlackore]

What is the compelling reason to build the front half on a slab? If you don't want a full basement in that area, a conditioned crawlspace would allow you to access the entire floor area.

[Chopsaw]

15 minutes ago, MCassady said:

but floor registers throughout the house aren't an option because the front half of the house will be built on a slab.

 

You might want to check with a local installer about this but it may not be impossible to run ducting under the slab as I have seen it done even though it is not always ideal.

 

Or what Robert just said.

[rlackore]

4 minutes ago, Chopsaw said:

 

You might want to check with a local installer about this but it may not be impossible to run ducting under the slab as I have seen it done even though it is not always ideal.

 

I agree that ducts under the slab are not ideal, but they are a possibility if all else fails. I've used attic mechanical rooms with success, sometimes in combination with a hot roof so the entire attic is conditioned.

[BrownTiger]

Normally you want ductwork:

1 center of the house

2 never install trunc / major supply underneath of wall with eves.

3 ideally supply's and returns should be in a condition space. 

4. You should have a central return

5. Unless you are planning to undercut every door you should plan for returns.

6. Readup on jump duct vs dedicated returns.

0. Consult an expert

[joey_martin]

How about carving out a corner of the pantry to place the AHU. That would be a little more centrally located.

[MCassady]

19 hours ago, rlackore said:

What is the compelling reason to build the front half on a slab? If you don't want a full basement in that area, a conditioned crawlspace would allow you to access the entire floor area.

This design started as a slab on grade, but the owners decided they want a half walk-out and suggested them stem wall through the middle of the house. I'm going to see what they think about the crawlspace idea. Thank you.

[MCassady]

19 hours ago, Chopsaw said:

 

You might want to check with a local installer about this but it may not be impossible to run ducting under the slab as I have seen it done even though it is not always ideal.

 

Or what Robert just said.

Thank you for the suggestion. I'm going to ask a local installer about it. 

[MCassady]

18 hours ago, rlackore said:

 

I agree that ducts under the slab are not ideal, but they are a possibility if all else fails. I've used attic mechanical rooms with success, sometimes in combination with a hot roof so the entire attic is conditioned.

Thank you for the suggestion. I'll talk to the owners about that option.

[MCassady]

18 hours ago, BrownTiger said:

Normally you want ductwork:

1 center of the house

2 never install trunc / major supply underneath of wall with eves.

3 ideally supply's and returns should be in a condition space. 

4. You should have a central return

5. Unless you are planning to undercut every door you should plan for returns.

6. Readup on jump duct vs dedicated returns.

0. Consult an expert

This is very helpful. Thank you. Quick question. Why should someone avoid putting a major supply underneath a wall with eaves?

[MCassady]

35 minutes ago, joey_martin said:

How about carving out a corner of the pantry to place the AHU. That would be a little more centrally located.

That's where I had it located originally, but the owners wanted it moved for more pantry space. 

[Gawdzira]

My mechanical installers would generally want a system for each floor. It is really hard to balance between floor.

 

[lbuttery]

If the house is in the Southern US with high humidity be wary of crawl spaces

 

I just bought a winter home in NC built in 1974

with crawl space under the entire house - huge mold issues

and it is very common in the South

 

I am in the process of spending $10K to remediate the mold, remove the insulation, add insulation batts on the walls

then add a de-humidifier and sump pump and close all vents and encapsulate with a liner (equivalent to a swimming pool liner)

 

the vendor in NC is doing a similar process to what this TN vendor is doing

they have many videos explaining the issues and solutions

https://crawlspaceninja.com/

 

Lew

[ACADuser]

Working in Florida as I do I would show a large recess into the trusses in the garage ceiling.
The AHU would go there. All ducts would go through the attic.
If the customer is going to remain in the house for say 15-20 years I would suggest a conditioned attic.
The insulation will cost more but AC saving, in the long run, will pay off. ( I don't have the actual numbers)
Also the AC tonnage drops.
It's very rare to see floor registers in Florida. Usually, a Northern builder trying to build in Florida.
If you need a register in the basement then a chase from the attic is easy to hide.

It's also rare to see a basement in Florida. The water table in most places is too high.

 

[MCassady]

On 1/20/2019 at 10:57 AM, ACADuser said:

Working in Florida as I do I would show a large recess into the trusses in the garage ceiling.
The AHU would go there. All ducts would go through the attic.
If the customer is going to remain in the house for say 15-20 years I would suggest a conditioned attic.
The insulation will cost more but AC saving, in the long run, will pay off. ( I don't have the actual numbers)
Also the AC tonnage drops.
It's very rare to see floor registers in Florida. Usually, a Northern builder trying to build in Florida.
If you need a register in the basement then a chase from the attic is easy to hide.

It's also rare to see a basement in Florida. The water table in most places is too high.

 

Thank you. I'm from Northwest Florida and the lot slopes quite a bit, so this is one of the few times it makes sense to build a basement in Florida. Thank you for your suggestions.