HVAC options for small garage size studio

Hi. Very confused about ventilation for my small garage size studio. It's the only thing holding me up from finishing it.....! The studio is divided into a control room and live room. I'm going to install a mini split in the control room but fresh air is still a problem. (studio is a 2 leaf system with core filled blocks as outer leaf and air gap then 16mm gyprock as inner leaf) Gotta say the studio building has been very easy so far compared to the HVAC thing. I've had a few guys come out to give me quotes and they just don't get what I'm trying to achieve. It's getting very frustrating as I'm not sure what to tell them. I have read the Rod Gervais book and have looked at various posts on this forum. Sorry but it's still not computing in this head of mine so I'm finding it hard to tell these guys exactly what I want. Shouldn't this be simple as the rooms are so small? Am I over-thinking this? The ventilation ducting will be in the roof space of the original shed (outer leaf). Here are the three option I have come up with. (pictures below if that's easier) OPTION 1: actively vent air into control room via baffle box. Passively vent air out via baffle box. actively vent air into live room. Passivley vent air out via baffle box. (probably the best option??? but means I need 4 holes in my studio - also seems a bit excessive for such a small studio?) OPTION 2: actively vent air into control room via baffle box. Passively vent air into live room via baffle box. Passively vent air out of live room via baffle box. (if this is OK it means the live room will get a bit of air con mixed in with it's intake) OPTION 3: Actively vent air into control room and live room via baffle box into Y splitter. Passively vent air out via y split into baffle box (the most simple, only need 2 holes in the studio..... but can you use Y splitters?) . Is what I'm doing making sense at all? Going from outside the building straight into a baffle box? Putting the fan at the start of the run? Is 150mm (6") duct alright or should it be bigger? How long should the ducting be? Any other suggestions will be GREATLY aprreciated as I feel I'm at a loss. Here are some (very bad-sorry) pictures of the options. (they are back to front starting at option 3) Black asterix = fan Yellow rectangle = baffle box Pink line = ducting and direction grey square = vent (mini split will be on the wall with the door) Thank you!!! Cheers, Adam.

Very confused about ventilation for my small garage size studio.

It's a very confusing part of studio building! HVAC is a lot more complex than it appears at first glance, and I'm more and more convinced that it is the single most overlooked part of home studios.

The studio is divided into a control room and live room. I'm going to install a mini split in the control room

What about the live room? That needs cooling and dehumidifying too!

Gotta say the studio building has been very easy so far compared to the HVAC thing.

:) Yup. It is complicated, for sure.

I've had a few guys come out to give me quotes and they just don't get what I'm trying to achieve. It's getting very frustrating as I'm not sure what to tell them.

The problem is that average HVAC contractors simply never have to deal with acoustically isolated rooms in their normal business, so they do not know how to do it, and don't understand the issues. Normally, sound is just not even on their radar for most installations, and they were never taught anything about it in their training, so it's not surprising that they don't get it. Frustrating, but not surprising.

Shouldn't this be simple as the rooms are so small? Am I over-thinking this?

No, you are NOT over-thinking it! Not at all. The fact that you are so confused suggest that you are thinking about it the right way. And not, just because a room is small does not make HVAC any easier. In fact, from one point of view, it makes it harder and even more critical. Proportionally, small rooms need more fresh air than large rooms, since there is less total oxygen in a small space, and CO2 builds up faster, so you need to deal with it much more than in a larger room, if you hope to stay alive for very long... :)

OPTION 1: actively vent air into control room via baffle box. Passively vent air out via baffle box. actively vent air into live room. Passivley vent air out via baffle box. (probably the best option??? but means I need 4 holes in my studio - also seems a bit excessive for such a small studio?)

That is, indeed, the correct way of doing it. And is not excessive: small or large, the basic plan is still the same.

OPTION 2: actively vent air into control room via baffle box. Passively vent air into live room via baffle box. Passively vent air out of live room via baffle box. (if this is OK it means the live room will get a bit of air con mixed in with it's intake)

It's always a bad idea to vent from one room into another. The problem here is basically that the live room gets stale air, that is low in oxygen and high in CO2 (as well as odors and other unpleasant stuff), and is also humid and warm. Not a good plan.... You don't live in the USA, so you are not subject to USA laws, but there are very strict controls on that sort of issue in the USA. I imagine that Australia has similar laws. So regardless of whether or not it is a practical option, it is possibly an illegal one...

OPTION 3: Actively vent air into control room and live room via baffle box into Y splitter. Passively vent air out via y split into baffle box (the most simple, only need 2 holes in the studio..... but can you use Y splitters?) .

It is possible to build one oversize silencer box as a single intake, and split that to the individual rooms, but you cannot do that for the exhaust: mixing two stale air exhaust streams is really hard to do, as you have to balance the pressures and speeds perfectly so that one stream does not overwhelm the other, and feed some air backwards, the wrong way.... So for input you can split, as long as the silencer is twice the size, but not for the return.

Is what I'm doing making sense at all? Going from outside the building straight into a baffle box?

Yes. But depending on how much isolation you want between rooms, and also how much you want from inside the building to outside, that might not be enough. It is the start, but not the complete system. How much isolation do you need? What are your goals there? (In terms of decibels).

Putting the fan at the start of the run?

The fan can go anywhere: at the inlet, in-line with the ducts, or on the outlet. Since the rooms are basically air-tight chambers, it doesn't matter too much if you blow fresh air into the intake duct and let it "run out" the outlet due to the over-pressure, or if you suck it out the outlet duct and allow fresh air to be drawn in through the inlet due to the under-pressure. You could also go for "overkill" if you want, and put fans in both ends, but they you have the problem of balancing them, so they are not fighting each other.

Is 150mm (6") duct alright or should it be bigger?

That depends on the speed and volume of air that you need to move through each room. Rod shows how to do the calculations for that in his book, so if you work through that section you should be able to come up with the two key numbers: How many cubic feet per minute of air do you need to move through each room, and how fast will that flow through a 6" duct? If the answer to the second question is above about 300 fpm, then you need a larger duct, or you need to split into two 6" ducts, or you need to widen out the last few feet of duct to fit a larger register. The goal is to have air arriving at the registers in the room at a speed of less than 300 fpm, and with sufficient volume to meet the needs of the room, basic on room size and occupancy.

How long should the ducting be?

As long as possible, and as shot as possible! :D Sorry, that's not very helpful, but that's actually the way it is. It needs to be as long as possible so that you can put as much distance as possible between the "noisy" end and the "quiet" end, as sound diminishes over distance. But static pressure increases with distance (especially with small duct, like 6"), and that affects how the fan works, so it needs to be as short as possible in order to not present a static pressure load that is too high for the fans to handle. Static pressure (or "back pressure") is just the resistance to the flow of air that is presented by the entire system, including the ducts, silencers, registers, and the rooms themselves (although it is probably negligible for the actual room). You can figure it out from tables and charts. The fan you get should also have a table that tells you how much air it will actually move when it "sees" a certain load. So a fan might be rated at 250 CFM, for example, but that is normally the "free air" rating, which is measured with the fan just sitting out in the middle of nowhere, not attached to any duct, but when you put it on a duct system that has a static pressure of half an inch, it will only be able to move 170 CFM, and for 0.8 inches it might only move 120 CFM. Those are just examples!!! All fans are different in this aspect, so check the manufacturer's data sheets carefully to make sure that the one you choose can produce the correct flow rate for the actual static pressure in YOUR system. Like I said: it is complex, but not impossible to understand.

(mini split will be on the wall with the door)

Try to bring the supply register as close as you can to the intake of the mini-split unit, so that most of the incoming air is cooled and dehumidified as soon as it hits the room. I'm going to PM you some other stuff that I cannot post publicly, for various reasons, that might help you understand this a bit better. - Stuart -

OK. Thank you so much. I love this forum. So before I discuss duct size and how much air I need etc I need to know in VERY simple terms if this sounds right (as I need to explain it to a HVAC guy - and myself). As I have a control room and a live room I’ll do the exact same in both rooms. (although the control room will have a mini split where I’ll position the inlet of the supply air near the mini split outlet). What to tell a HVAC guy: SUPPLY: “Hi HVAC man, hope you are having a good day.... I need a wall mounted fan on the outside of my wall that then goes into a ‘silencer box’ which I’ll supply. It is then ducted via flexible duct to an air register. The flexible duct will have a few bends and be quite long (as long as the fan is powerful enough). Before the duct gets to the register it will increase in size via an adapter (to slow the velocity).” RETURN: “The return register will be positioned on the other side of the room to the supply register. It will be passive. It will have the same size duct all along and before it leaves the room it will go through a ‘silencer box’.” In it’s most simple form is this right? Have I missed something ‘simple’? Thanks! Adam. I've attached a picture as above. Again.... Black asterix = fan Yellow rectangle = baffle box Pink line = ducting and direction grey square = register Red box = mini split All ducting in outer leaf roof cavity.

What to tell a HVAC guy:

sounds about right! But there's still the question of why you have a mini-split in only one room: How are you going to cool and dehumidify the other room? - Stuart -

Thanks Stuart. The goal is to have a mini split in both rooms but to get the studio finished sooner rather than later I can only afford to get one now, one later. (open the door in between takes for a while I guess). One last question.... Besides the mini split installation do people install their own ventilation systems or is it sensible to get Mr HVAC man? (installation doesn't seem too hard now I'm getting my head around it). Thanks so much once again! Adam.

One last question.... Besides the mini split installation do people install their own ventilation systems or is it sensible to get Mr HVAC man? (installation doesn't seem too hard now I'm getting my head around it).

The mini-split itself needs special installation, as it has to be charged correctly with the refrigerant gas, and checked for leaks, etc., so you do need to hire an expert to do that for you. But the ducts, silencers and fans you can probably do yourself, without too much hassle. If you look around the forum, you'll find plenty of threads where people have done it themselves, very successfully. If you can build the rest of the studio by yourself, then you can certainly do the ventilation system! :) - Stuart -