Opinions on garage ventilation/makeup air system

[ned3000]

I'm partway through setting up a ventilation system for my 700 sq. ft. garage. I have a good exhaust setup (2400 cfm fan) but now I need to deal with providing makeup air for that.

I thought I'd post my plan here to see if anyone else who's dealt with this has opinions or insights.

I'm thinking about adding a duct from outside w/ an inline fan (something like the FKD 12 XL here.) I was also considering adding a heater to that line, as I think it would cold fast with that system running (the garage is heated and insulated). This is the heater I'm looking at MUAH 12/10.

Other than that, I'd have an electrically controlled damper and some minimal high flowing filter. Since this setup would be in a closet in the house I was also thinking about adding a controlled inlet to mix a small amount of house air to get a bit more flow.

So, am I on track here or are there flaws with this plan that I'm not seeing?

 

[chinboys]

The make up air should be coming from an energy recovery unit. And it ought to be supplying make up air greater than or equal to what is being exhausted. Think clean room. And it helps if you have minimum air infiltration hence conduct a blower door test to fix the leaks.

 

[ned3000]

I was planning to accept that there will be some degree of negative pressure in the garage. It's attached to the house, so my thinking is better for any leakage to go house -> garage rather than the opposite. I looked at those energy recovery units, but I'm looking to move a good amount of air so that anything noxious is gone relatively quickly and those seem much more slow-acting.

 

[Airforce_NavyDAD]

It depends on what you're exhausting if an ERV would work or not. If it's dirty air/ fumes I wouldn't go with any Recovery. Like you said an Outside air duct tied into a Return of an Air Handler with a damper would suffice. An interlock that turns the fan on when you're exhaust is running and opens the OA. Tempering the Make-up air would be a different story.

 

[fitter30]

Just did a quick air change for a building 30x23x10
20 air changes an hour 2300 cfm
www.omnicalculator.com/construction/cfm
What are u going to do about heating and cooling the space? With just heating it will take a make up air unit.
Filter size for 2400 cfm using merv filter is 960 sq in. Using smaller filters will require more filter changes using 100% outside air.

 

[ned3000]

For makeup air, I'm planning on using this fan, and this heater.

No cooling. I'm only going to run the system as needed to remove contaminants, so I was planning on just dealing with the heat in the summer.

For the filter I was thinking of just using an aluminum "pre-filter" without a pleated one (like this). Less restrictive and (unless I'm missing something) I don't really need much filtering.

 

[American Locomotive]

What exactly is your ventilation system exhausting? It's far more efficient to have your make up air be supplied directly into a fume hood, as you don't need to spend nearly as much energy trying to condition it.

You're going to need A LOT of heater to keep the makeup air tempered.

• Assume 25° temp differential (Garage Temp 65°, Outdoor Temp 40°F)
• 1900 CFM make-up air fan
• 25° Temp Rise @ 1900 CFM = 51,000 BTU/hr, or 15kW.

Your supplier's biggest 10kW duct heater won't keep up. And even then, 10kW is a tremendous amount of power to plow. It would need to be on a 60A circuit. It would cost almost 6 cents/minute to run that heater in Massachusetts.

 

[ned3000]

@American Locomotive I was a bit concerned with the makeup air heating. As you said, it seems like a lot of power and not quite strong enough. Could you be a little more specific about what you're talking about with the fume hood? I'm kind of clueless about this stuff.

 

[American Locomotive]

Like is this exhaust fan for a paint booth or a welding area or something?

 

[ned3000]

Yeah, the issue is mostly welding and painting. Probably some other chemical processes moving forward.

 

[larry4406]

Following along....

I still need to install an active makeup air system for our kitchen as the house is too tight and the hood is too large. Currently we open a window when the hood is on.

I have been reading about this pressure controlled system. Can't seem to find any posts on the internet about actual installations which is concerning.

HVACQuick - AirScape Residential Make-up Air Unit

 

[American Locomotive]

Yeah, the issue is mostly welding and painting. Probably some other chemical processes moving forward.

When you look up commercial kitchen exhaust hoods or even higher end residential range hoods, they often divide the hood in to two parts. One part *****, the other part blows. The idea is that you create this kind of looping air flow that ***** everything out, without needing to pump tons of unconditioned air into the room itself.

 

[danski0224]

The hood analogy only works if the space being exhausted can be served with an exhaust hood.

 

[danski0224]

When you look up commercial kitchen exhaust hoods

There's usually a make-up air unit on the roof for heating. Sometimes there's a condensing unit bolted to the roof of the make up unit.

Given that they pull in 100% outside air (OA), the btu rating (heating) is in the hundreds of thousands.

Someone I know was fixing a common area 100% OA heater for a multi story building with 1600kW of elements. He said the breaker had a 24" handle on it.

 

[fitter30]

10kw= 34,100 btu's
BTU Output = Temperature Rise (∆ T) x CFM x 1.08

 

[ned3000]

The only systems that I could find that do any kind of heat exchange (other than huge $$$ commercial units) were in the 50-400 CFM range, so if I want > 1000 CFM I think I'm stuck with heating outside air.

It seems like the 10kW heater that I linked (this one) would work OK if I kept the CFM down around 1000, depending on how cold it is outside. Then when it's warmer I can let it rip at the higher speed.

They do make a 20kW version. I have the power available (there's a 150A panel in the garage that's right next to the where the heater will be) but it seems like overkill. I kind of don't want to deal with 4 AWG wire.

 

[Kaizen]

Personally I think you are getting way too complicated. I would not put any kind of filter on the welding or painting air going out. So that rules out any kind of erv or hrv. If you just had a hang out spot to drink beers and watch footbal the the hrv would be my choice.
A simple duct with a baffle can provide welding make up air and don't connect to the inside of the house at all. You could be out spraying and have something change inside and have all that sucked back in. Even though you have fans directing if a more powerful source is involved it can pull back through.

 

[American Locomotive]

Is this just going to be a giant exhaust fan in the ceiling? Will you have a hood? A paint booth-style setup?

 

[ned3000]

Personally I think you are getting way too complicated.

I'm surprised this comment took so long. Usually when I describe a project I'm planning that's the first response.

There's a couple of problems with passive makeup air: 1.) The size required is huge if there's a significant amount of exhaust airflow. ChatGPT says I would need 8 square ft. I could just partially open the garage door but that leads to 2.) It will get cold pretty quickly without a heater.

I'm leaning toward setting up the whole thing in the garage now (not in the closet) so there's less of a concern about airflow into the house. Also was going to add a couple of electrical failsafes so that it's not possible to run intake fan without exhaust, etc.

 

[ned3000]

Is this just going to be a giant exhaust fan in the ceiling? Will you have a hood? A paint booth-style setup?

The exhaust fan is in the wall. No hood or booth or anything at this time.

 

[dscheidt]

There's usually a make-up air unit on the roof for heating. Sometimes there's a condensing unit bolted to the roof of the make up unit.

Given that they pull in 100% outside air (OA), the btu rating (heating) is in the hundreds of thousands.

Someone I know was fixing a common area 100% OA heater for a multi story building with 1600kW of elements. He said the breaker had a 24" handle on it.

Depends on where you are, and the age of the hood. Until fairly recently, it was hard to get AHJ to allow performance testing (where the hood installer or designer demonstrates that it actually works) instead of prescriptive cfm numbers. Since the prescriptive venting requirements can be very high, there's a real incentive to reduce it, and also put much of the make up into the hood where it doesn't need to be conditioned. Payback is pretty fast where the heat or cooling season is long.

 

[American Locomotive]

There's a couple of problems with passive makeup air: 1.) The size required is huge if there's a significant amount of exhaust airflow. ChatGPT says I would need 8 square ft. I could just partially open the garage door but that leads to 2.) It will get cold pretty quickly without a heater.

I really wouldn't trust any calculation ChatGPT makes about any topic. It still hallucinates and makes things up quite frequently.

I think really you need to identify what you're trying to accomplish with this fan. What are you exhausting? Paint fumes, welding fumes, saw dust?

 

[ned3000]

ChatGPT's number may have been high, but I've looked it up before and the recommended size of passive intake is surprisingly large (even if totally unrestricted).

As far as what's being exhausted, yes, paint fumes, welding fumes (not really too worried about that except for maybe zinc coating), fine sawdust from sanding etc. Also, like I said, I'd like to be prepared to handle whatever kind of chemical processes I might end up trying (most likely metal finishing, anodizing, plating/coating, etc).

In all of those cases I'd like to be able to take off the respirator in a reasonably short amount of time (and not freeze to death).

 

[BroncoAZ]

Following.

 

[WildBill]

Another approach would be a portable HEPA filter setup with a movable duct, we used them a lot at my last job when dealing with welding and lead grinding tasks. Like this but check specs for your application- https://www.amazon.com/Extractor-Pu...rification/dp/B0DKBD47PP?tag=atomicindus08-20

 

[u3b3rg33k]

ChatGPT's number may have been high, but I've looked it up before and the recommended size of passive intake is surprisingly large (even if totally unrestricted).

As far as what's being exhausted, yes, paint fumes, welding fumes (not really too worried about that except for maybe zinc coating), fine sawdust from sanding etc. Also, like I said, I'd like to be prepared to handle whatever kind of chemical processes I might end up trying (most likely metal finishing, anodizing, plating/coating, etc).

In all of those cases I'd like to be able to take off the respirator in a reasonably short amount of time (and not freeze to death).

Adjust your airflow requirements with source control.

Get yourself a plate HX (HRV) and do your best for source control. plate HX fouling can be mitigated with good filtration (cheap pleated prefilters (or washable expanded metal) where smoke can "condense" and MERV13+ media before the core. do not rely on the tiny HRV 'household' sized filters for "dirty" airstreams (get a filter rack or CFB from hvacquick, they're cheap). when in doubt, oversize the filter as large as practical (20x20x4", 24x24x4", etc).

plate HX will easily recover 50% sensible. then you can put a cheapo hanging electric/gas/hot water coil wherever like a normal garage.

check for used light commercial units on *bay or other sites. I bought a nasty one off the *bay and had to pressure wash it and the fans but i saved 90% off new.

otherwise just crack the garage door and run a 2' exhaust fan out the upper wall/roof. it'll be cold in winter.

 

[ned3000]

The idea of heat recovery is really appealing but from what I've seen it seems that they're mostly designed to gradually replace 'stale' air so the air flow volume is pretty low. With the system that I proposed I should be able to get well over 1000 CFM. Anything approaching that that I've seen for HRV systems is very large and prohibitively expensive (If I'm missing something let me know!)

I'm sure it's possible to score a killer deal on a used system on *Bay like you said, but I already have enough ongoing fixer-upper-that-I-got-for-cheap projects happening.

And as far as cracking the garage door, one of my stated goals was not to freeze to death.

 

[BroncoAZ]

I’m looking for something to extract weld smoke from my 34x21 shop also without freezing. I have a mini split that heats the shop nicely and don’t want to lose all the heat. I also don’t want to spend more on a filtering fume extractor than I did on all of my welding gear put together. Aside from cold I’m concerned about with the makeup air from an DIY extractor only setup is drawing in all that humid air into a dehumidified space. If I eventually installed another exterior door and a concrete pad I could do most of the welding outdoors to eliminate the issue from the shop. I will be wearing a respirator regardless.

For wood working I plan on using a hepa vacuum dust extractor, possibly the one from HF but maybe I’ll spend more. I can set that up for my miter saw and other tools. I was also considering making an adapter to convert my fixture table into a filtered downdraft table for sanding. I have a Jet AFS-1000b hanging from the ceiling to generally clean particulates from the air, it works fine but I want to control the dust before it gets that close to the ceiling.

 

[u3b3rg33k]

The idea of heat recovery is really appealing but from what I've seen it seems that they're mostly designed to gradually replace 'stale' air so the air flow volume is pretty low. With the system that I proposed I should be able to get well over 1000 CFM. Anything approaching that that I've seen for HRV systems is very large and prohibitively expensive (If I'm missing something let me know!)

I'm sure it's possible to score a killer deal on a used system on *Bay like you said, but I already have enough ongoing fixer-upper-that-I-got-for-cheap projects happening.

And as far as cracking the garage door, one of my stated goals was not to freeze to death.

you're thinking of residential units intended to provide code-minimum airflow.

Fantech SHR - 1,428 CFM - Heat Recovery Ventilator (HRV) - Side Ports - 24 x... | eBay

Fantech SHR - 1,428 CFM - Heat Recovery Ventilator (HRV) - Side Ports - 24 x 8" Duct - Exhaust Defrost. An aluminum heat recovery core provides improved heat transfer capacity while taking up less space than traditional cores.

www.ebay.com

that's a pretty good price for 1400CFM. I'd do that and slap a modulating heater on it's outlet.

 

[ned3000]

@u3b3rg33k Thanks for the link. I hadn't seen that particular product line in my searches. Definitely something to consider. That unit is big, heavy, and expensive, but the idea of not wasting all the heat in the exhaust air is a big draw.

I guess the question is how effectively that system would keep the temp. from dropping vs the original plan w/ the heater. You mentioned a heater on the output, which from my initial cursory investigation I believe would be desirable. I'm afraid at that point it's getting beyond what my budget is here.

Also, @BroncoAZ have you seen this page? That guy gets *way* in depth about duct collection.

 

[u3b3rg33k]

@u3b3rg33k Thanks for the link. I hadn't seen that particular product line in my searches. Definitely something to consider. That unit is big, heavy, and expensive, but the idea of not wasting all the heat in the exhaust air is a big draw.

I guess the question is how effectively that system would keep the temp. from dropping vs the original plan w/ the heater. You mentioned a heater on the output, which from my initial cursory investigation I believe would be desirable. I'm afraid at that point it's getting beyond what my budget is here.

Also, @BroncoAZ have you seen this page? That guy gets *way* in depth about duct collection.

if you're patient, you can sometimes find better prices, especially if something used shows up. performance is rated at 50% of sensible heat recovery (pretty standard for HRVs).

IMHO welding can be accommodated with even half-decent source control.
painting... it depends on how big a booth you're using. airbrushing RC cars or painting an entire car are quite different. autobody paint booths have hilariously sized equipment for a home garage. consider a PAPR/breathing air supply system?

I've got a harvey dust collector in a off-label use (plastic dust, not wood dust) and it works quite well for my needs. I found the traditional (cheap) filter bag-over-cyclone-over-trash bag units to be a ton of hassle and perform poorly.

 

[larry4406]

Passive make up air is joke when a hood is larger than meager. Here is a graph from Airscapefans.com. The context of the graph is for kitchen makeup air air.

I assume the graph is based on a "tight" house, so if your garage leaks like a sieve you are getting closer to a solution.

 

[Kaizen]

I'm surprised this comment took so long. Usually when I describe a project I'm planning that's the first response.

There's a couple of problems with passive makeup air: 1.) The size required is huge if there's a significant amount of exhaust airflow. ChatGPT says I would need 8 square ft. I could just partially open the garage door but that leads to 2.) It will get cold pretty quickly without a heater.

I'm leaning toward setting up the whole thing in the garage now (not in the closet) so there's less of a concern about airflow into the house. Also was going to add a couple of electrical failsafes so that it's not possible to run intake fan without exhaust, etc.

I mig weld in my shop without exhaust for long periods without much issue. Granted its a big shop. The make up heat just seems to be a waste in my opinon. Nice to be warm but tough to do both in our area. I had some epoxy to spray and set up the shop and lucked out on that last 60 degree day we had so i had several fans at the door sucking it out. Also used a good mask. I get it if you are going to be doing something a lot and its an investment but if its just spraying furniture or hobby stuff i'd aim for a room or a temp greenhouse in the garage.