Basement Ventilation
Hello! I am new to this site and have a question about basement ventilation and air quality. I am in the process of planning the buildout of a finished basement. I can’t get a straight answer from hvac contractors as to whether I need mechanical ventilation in my basement and if so what kind. My house which is a 2019 build, is located in Massachusetts, 30 minutes west of Boston. I have about 4500 sq ft of living space above grade, presently with an unfinished basement. The basement buildout plan is to have about 1200 sq ft of finished space for a recreation room, gym, and half bath, plus another 300 sq ft of unfinished space for a mechanical room and utility room. There presently is no heating or cooling supply in our basement, but we are planning on installing a ductless mini-split as part of the buildout. We have a SaniDry XP dehumidifier which runs constantly during the humid summer months but does not run during the winters. The bathroom to be built will have an exhaust fan. We have a radon mitigation system which does a nice job exhausting radon from the interior. We have an Aprilaire ERV which is tied into the ductwork that provides heating and cooling to the finished portion of our attic and second floor, but no other mechanical ventilation that I am aware of on our first floor or basement. Our basement does have windows, but they are difficult to open and close so they remain closed. We also have walkout stairs from the basement to the exterior backyard of our house, which is used during the summer but rarely during the winter. Given the foregoing, do I also need an ERV that will be ducted to the various spaces to be finished in my basement? Or perhaps a Panasonic Whispercomfort Spot ERV which would only exchange air in the to be built recreation room? Or would a simple make-up air system suffice? Or can I save money on my project by eliminating any addition of an ERV from our basement buildout? Thanks in advance for your thoughts!!
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My guess is the basement is inside your conditioned space and is more or less the same temp and humidity as the rest of your home without any register in the basement. Adding a register or 2 should not cost much and generally the equipment is plenty big enough.
Someone will be along soon to tell you absolutely every home needs a HRV ventilation system. Personally, I am not so convinced. The only thing installing one could hurt is your wallet. If your population density is very high like 800 SQF per person on side 24-7 and you had a blower door test under 1 ACH50 OK .
Do you know the current radon number?
Have you had a blower door test?
I doubt the new mini split is needed.
Hi our basement is always pretty moderate in temperature. It gets down to about 50 degrees in the winter and up to 78 degrees in the summer. So we are adding a minisplit for cooling, heating, and dehumidification.
What I am not sure about is whether we need the ERV/HRV in our basement giving all of the factors mentioned in my original email.
I don't know population density and no blower door test has been done. Radon is still at the same level as when we installed it a year ago.
Consider as part of your build out getting windows that are easier to open. There might be fire safety issues here that you would be required to address if you finish the basement. Basement windows are often cheap single pane and perhaps replacing them won't cost a lot and you could still improve your energy efficiency.
Do you have forced air on the first floor? Do you have an old forced air system with registers in the basement? If you can run a fan that circulates air between the basement and the rest of the house that lessens the need for ventilation in the basement.
The basement windows are sliders from 2019 build. The problem is not really the window itself, but rather because the window is so high up on the wall that no one can move the pane without getting on a ladder or chair.
We do have forced hot air on our first floor; the furnace and ductwork are located in the basement, but it only services the first floor and does not condition the basement. Will consider a fan, but we are trying to bring in fresh air too, not just circulating air.
Basements are often leaky around the rim joist (and the walkout area in your case) and with open floor plans may have good circulation. You say no mechanical ventilation, but is there a forced air system for the basement and first floor that circulates air?
Get a CO2 (and ideally other IAQ as well) monitor- that's the only way to figure out what is actually needed in your house. Then spend time down there and see if the IAQ is strongly affected. Two stress tests would probably be working out (a lot of CO2 at once) and sleeping (a lot over time).
The only issue with testing now is that you might end up in the build out sealing off leaks that are providing fresh air.
No forced air supply to the basement currently. Good point about sealing the fresh air supply out; so it is fine without an ERV because the wall is currently just concrete. Once we insulate and blue board, we might need more ventilation. I don't know how to get the monitors for CO2 and IAQ?
This is a good, basic monitor: https://www.getawair.com/pages/element. You will almost certainly find elevated CO2 levels if you don't include some sort of ventilation, unless you build a very leaky space. CO2 is not a major health concern in the way that CO is, but it has a big effect on wakefulness and well-being.
If you have no ventilation or mixing from a forced air system then you are relying on leaks for fresh air and the basement door for some mixing. Code might require adding ventilation when building out. When you test CO2 you should make sure to test on a calm day- on a windy day a lot of fresh air can be forced in.
Ok this makes sense. Our house is pretty air tight. While we will have a minisplit and high capacity whole house dehumidifier running in the basement, I agree that we might need additional mechanical ventilation. I have asked an HVAC company for a proposal to install a Panasonic WhisperComfort Spot ERV. Do you or anyone else on this site have any experience with this Spot ERV from Panasonic?
I have looked into it several times but as I recall it shuts down in low temperatures so it's not a good fit for my cold climate location.
Thanks for the input on air quality monitors. Will check it out!
Code might require adding ventilation when building out.
If Code might require adding mechanical ventilation when building out my basement and Panasonic WhisperComfort Spot ERV is not a good solution for the cold climate of Massachusetts, what do you recommend I do? Adding a full ERV or HRV with ductwork into each room of my to-be-built out basement does not appear to be a viable option as it could cost between $5K - $10K. Significantly, I already have an Aprilaire ERV that exchanges air on the second floor of my house.
It looks like the WhisperComfort unit just exhausts when it gets cold- which would be an okay match to an install that exhausts bathrooms out the ERV. If bathroom exhaust does not go out the ERV recirculate when freezing outside is better. Panasonic Intellibalance models recirculate and are more reviewed here. The Broan AI series has a lot of nice intelligent controls, particularly with the optional LCD screen, but maybe you don't need that. If you don't want to worry about defrost cycles get a RenewAire. You could set it up to run at its lowest level normally and trigger it via dry contact to boost on high when the basement lights are on.
Duct work for the ERV might not be that expensive if you can locate it centrally to the different rooms and use a single exhaust intake.
I am not an expert so listen to them… I would absolutely add ventilation. IAQ is very poorly understood and not regulated so it is up to you to make sure the air in your home is healthy to breathe.
I’m not so sure about the ERV tied into your heating/cooling system upstairs. My engineer said this is not good for reasons someone else on here can explain better than me, I wanted less ductwork but ultimately listened to the engineer.
It does depend on occupancy and obviously the air tightness of your home. But if it is reasonably tight, I’d be adding ventilation (again, not as an expert just as a health conscious person). Especially if you do not open windows/doors down there. We put in a whole home ERV with dedicated ductwork, the basement will have a big fitness space and as someone mentioned above… CO2! If you can spend money on finishes, spend money on ventilation first!
My basement was finished without putting in a ceiling- highly recommended. It saves money and makes it a lot easier to work on the house. They did spray paint it black to make it less noticeable (I don't necessarily recommend this, but it is an option). We have HVAC duct work, etc coming from the basement . I have but duct sealant on some leaky ducts that I wouldn't have noticed. I have ran cabling to and from the basement. I have secured monkey bars for the kids to the joists.
graygreen,
To me T-bar ceilings offer a good compromise between having a basement space feel fully finished and still allowing access for services - and the new ones don't look like a 1970s government office.
Agghhh! We are set to drywall the ceiling, I think the sheets are being delivered in a couple weeks. I did wonder about spraying it all black but that idea came and went pretty quickly.
What are the new t-bar ceilings?! Initially the idea is horrifying, aesthetically, but it does make sense to have access somehow. I originally wanted to do a wood panelled ceiling in the basement but it fell to the bottom of the priority list so we figured to just drywall it while we’re doing everything else. The mechanical room is pretty large and that won’t have drywall on the ceiling.
Building a house is such a headache! But the monkey bars sound fun 😉
I am putting in an ERV in the basement attached to existing ductwork. No need to cut up drywall. Noticed a duct under the dining room had rusted (liquid spills) and replaced it. With that being said, check your fire code. Another option- it’s actually possible to use drywall as ceiling tiles.
Izzza,
You can get suspended ceiling tiles in pretty much any material or profile you can think of now. Lots of nice wood ones:
https://www.pinterest.com/pin/acoustic-ceiling-tiles-ceiling-tiles-ceiling-design-modern--349943833534754647/
Finished basements are pretty common here and they are universally connected to the central HVAC.
A reasonable insulated and sealed basement heat and cooling loads are pretty modest and since most HVAC systems are well oversized, this should not be an issue. There is not much point of a separate HVAC unless you are looking to turn it into an ADU down the road.
The extra rooms do require additional ventilation capacity, if there is nothing on your existing air handler for the main floor, now might be the best time to add one to handle both spaces. The stale air pickups could all be taken from the new bath and gym and the fresh air supplied to the air handler.
Basement cooling loads tend to be mostly latent which is generally not handled well by a standard AC unit, so the dehumidifier needs to stay even if you add vents from the HVAC or a mini split.
Absolutely recommend an ERV especially to your gym. I have a basement gym in a semi finished space with a fresh air supply from an ERV and still can reach up to 2k CO2 even on boost mode (really need a return also in that room). I agree with Monitoring your space, including CO2, Rh, and radon to get a better understanding of how your basement behaves. The space will be much more pleasant with moving fresh air.