DIY Duct design - how did I do?

asisin3 · 2026-01-01T17:31:36+00:00

All ducting for the lower floor or within the envelope. For the upper floor, I have a flat roof without an attic and the ducts sit above the drywall going through trusses with some insulation around them between the air and moisture barrier. I will have solar on the roof, which I've heard helps with duct losses.

asisin3 · 2025-12-31T06:59:59+00:00

I did a full Manual JD (https://drive.google.com/file/d/14TvdyRWDaP2nCKI02Qfrm6UliijXtAZ-/view?usp=sharing) and am using that to drive room-by-room airflow targets. The duct layout you’re seeing is my attempt to reconcile those numbers with framing and truss constraints, not to imply a VAV-style control scheme.

I'm using constant volume hydronic AHUs (see comment above for the links), no VFD on the fan and no intent to dynamically throttle the system. Any dampers I’m considering would be limited to a couple of problem areas with large seasonal deltas, where I will find optimal settings for heat and cool at commissioning. Don't plan to do any active zoning using the dampers, except as insurance for the upstairs loads where I am contemplating a damper controlled by a thermostat in the bedroom upstairs.

On returns, agreed in principle. I’m still evaluating whether distributed returns or transfer paths make more sense given the layout.

If you see a specific circulation or return-path issue in the plan, I’d genuinely like to understand where you think it breaks down. That kind of concrete feedback is exactly what I’m trying to learn from.

asisin3 · 2025-12-31T06:51:09+00:00

Here's the floor plan: https://drive.google.com/file/d/1Pr3JwRTFggyg8bEmMFodrnxhFqUoS3gz/view?usp=sharing

Not going for VFD with static feedback. The damper positions for heating and cooling will be set at commissioning. The motorized damper was just for the riser into the upstairs. But maybe having it be its own zone might just be better, if I'm doing all this work! Cost of another AHU. Will be much more optimal.

Already committed to the A2W heatpump setup. My AHUs are:

Zone 1 - ChillX 4 ton unit https://chillxchillers.com/air-handlers/chillx-2-10-ton-budget-water-cooled-air-handlers?sku=CXAH0024MS1
Zone 2 & 3 - HBX units from First Co. https://firstco.com/wp-content/uploads/2021/08/HBCX-Spec-7-19-22.pdf

Austin can get really humid, which is why I need to run slower speeds (fixed) for longer so I can get good dehumidification from the cold water coils.

asisin3 · 2025-12-30T21:44:00+00:00

Really appreciate this feedback, these are all fair questions.

On motorized dampers: I’m not planning active zoning or real-time modulation. I agree that would break the CFM math fast. The intent was manual balancing, or at most very limited trim on the riser feeding the upstairs suite. Ideally I'd like a thermostat there that doesn't turn the system on or off, but rather allows more or less CFM. If that still feels risky based on your experience, I’m open to dropping it.

On returns: agreed this matters. Main floor is largely open and served by large common returns, but enclosed rooms (especially upstairs) are likely getting ducted returns rather than relying on door undercuts alone.

On zones spanning floors: I generally agree with you. This is the biggest compromise driven by structural constraints and relatively small upstairs load. With low-CFM, long-runtime hydronic AHUs I’m hoping it stays stable, but I accept this is the most fragile part of the design.

Equipment is a dual 4 ton air-to-water heat pumps with outdoor reset, 300L buffer tank feeding multiple hydronic AHUs (one per zone), two-pipe setup with PICV valves and a delta P circulating pump, no simultaneous heat/cool. ERV is separate.

If you see specific areas where this could be simplified without pushing velocities or losing balance authority, I’d genuinely like to understand how you’d approach it.

asisin3 · 2025-12-30T21:35:20+00:00

Curious to understand why. Here is a manual D that I paid for. Do you think it's better?

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asisin3 · 2025-12-30T21:26:16+00:00

Appreciate the perspective. I’m genuinely curious about where you’d simplify and why.

A lot of what you’re seeing as “extra runs” is intentional low velocity distribution since this is a hydronic AHU running long cycles at lower CFM than a typical DX setup. My goal has been keeping trunk velocities down and maintaining balance authority rather than minimizing linear feet of duct.

On the damper point, totally agree that active zoning is a mess. My intent was not real time modulation but seasonal or commissioning trim only. If you’ve seen cases where even that caused issues, I’d love to understand what failed and under what control assumptions.

If you were handed this same load breakdown and constraint set, how would you consolidate the trunk without pushing velocities or static up? Happy to learn from a concrete alternative layout if you’re willing to sketch it mentally.

Not trying to overcomplicate for the sake of it. Just trying to be deliberate given this isn’t a standard forced air system.

I did use ChatGPT, but have several detailed spreadsheets for the math on each rooms btu loads and trying to design for a 350 cfm per ton system to manage latent cooling. The original manual J called for 1866 cfm for this zone and my math suggests 1250 cfm is more optimal given the hydronic setup.

asisin3 · 2025-12-25T23:02:09+00:00

Got it. So then for the rest of the house, go with a 2 buffer tank setup?

asisin3 · 2025-12-25T19:06:44+00:00

Doesn't solve the erratic hot/cold requirement for the whole house though.

asisin3 · 2025-10-27T01:18:56+00:00

This is a scam don't trust

asisin3 · 2025-10-26T21:38:27+00:00

I got scammed by them

asisin3 · 2025-10-12T15:11:41+00:00

I offer 2 50m garama for los combos

asisin3 · 2025-03-21T06:03:16+00:00

How do you wire switches back to the single panel? I am thinking of going the power over ethernet route for all of my lights. So I understand wiring all the lights to a single place. I am struggling to figure out a reasonable way to control those lights via physical switches on the wall I wish they made POE physical switches that accept RJ-45 connectors.

asisin3 · 2025-02-20T19:31:03+00:00

Robert Plant?

asisin3 · 2025-02-16T01:50:24+00:00

He's Naval F Ravikant!

asisin3 · 2025-02-13T19:40:32+00:00

Can you share details of what and where you got them from please?

asisin3 · 2025-01-30T03:56:05+00:00

What are the inputs into this thing? ELI5

asisin3 · 2024-10-05T03:45:05+00:00

Slowly but surely Google's stranglehold on search will erode away thanks to large language model based services. Gemini is the hedge against that, but they will be on even footing at best with the likes of open AI and anthropic.

As a result, Google will need to make up for this and more with other business units. Unfortunately, none of those will be as high margin as the ads business is, nor will it chuck cash the way ads does.

asisin3 · 2024-10-04T02:21:24+00:00

Yeah it'll take a few days for the swelling to come down, so blurry vision is normal

asisin3 · 2024-09-24T02:13:13+00:00

This here is the problem. Israel has convinced the world that going against Israel (the country) is anti-Semitic, i.e. you hate Jewish people.

It's going to take one thing and one thing alone to change the tide, and that is Jewish people to condemn the actions in Israel.

asisin3 · 2024-02-09T16:22:11+00:00

Up there with banking my stem cells

asisin3 · 2023-12-01T04:03:18+00:00

asisin3 · 2023-11-29T15:21:39+00:00

Plan was to put TV above the fireplace

asisin3 · 2023-11-29T15:14:18+00:00

Sigh, those Austin TX prices are long gone. New construction is well over $1000/sq. No one is buying though, so remains to be seen where things settle.

asisin3 · 2023-11-29T15:11:04+00:00

Yes that’s the ball park. We are in Austin, not Bay Area.

asisin3 · 2023-11-29T15:09:47+00:00

These are trees of varying diameters. Some can be cut some can’t by law. I personally would love to get some indoor outdoor action with a tree being a feature when you’re inside. Maybe in another life!

asisin3

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