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Help on ERV Solution for Basement

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10K views 25 replies 4 participants last post by  pecmsg  
T
#1 ·
Hello Everyone,

I'm trying to solve 2 issues with 1 solution.
My Radon levels are at the low end but if the house stays closed with no windows open (winter) it does start to go up. I had a team come in and said just open a window once a week for 1hr but the real issue is my house is under a pretty big negative pressure because I have a kitchen exhaust range and 6 bathroom fans with no make up air system. They said from experience if I add a makeup air solution or ERV I'd be good.

My basement as normal basement is humid and has a "musty smell" the temperature is always hovering between 68-73 all year round so the HVAC isn't on enough to remove humidity. So I had installed a dedicated humidifier in the mechanical room which reduced the humidity from 65% to 50% in mechanical room and 60% to 55% in conditioned area.

2 Questions.
1) Do I need TWO ERV systems or can I use one?
2) Which system would you recommend?
Clean Comfort, Fantech, Panasonic, Broan, etc.


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#2 ·
ERVs are a nice product but not sure if it will help all of your problems.

Most ERVs are designed for equal flow so X-cfm in X-cfm out X being dependent on the brand and model. It will exchange your air but it will not eliminate the negative pressure in the house unless it can be balanced to overcome all the equipment that creates the negative pressure in the house. With all the items listed that may take a commercial unit rather than a normal residential one.

Having said that if the ERV can be positioned to where the exhaust from the bathroom exhausts can be routed through the ERV so it actually replaces the exhaust fan then you only have to deal with the kitchen hood which if big enough may be done with a fresh air intake on the hood.

May not be ideal but it's one way of improvement. Ideally you would want a slight pressurization of the house, just enough so it is not neutral or negative.
 
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#3 ·
Your basement space and house may be better served by using make-up air ventilation only. You have many exhaust device that cause negative pressure and will suck in more soil gases. There are dehumidifiers that have Merv 13 air filters that have fans that will bring in exact amounts of fresh air, mix the fresh air with house air, filter the air and and duct the air to basement or multi areas. This best done on a steady trickle bases. This arrangement will dehumidify when ever the indoor %RH is above the desired levels.

Might you have one of these ductable dehumidifiers. There will be a big benefit in keeping the entire home <50%RH and with fresh air.

The whole house dehumidifiers that are designed to do this are the Santa Fe Ultra, Broan, Trane,etc.- with the fresh air option. The benefit from the ERV is minimal
compared to the benefit.

Keep us posted.

Regards Teddy Bear
 
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T
#4 ·
****! One part I forgot to mention which is important.
The house has a basement, first floor and 2nd floor. 3 independent HVAC systems, that's why I didn't look into the whole home humidifier as I'd need 3! 2nd and 1st floor are always around the happy 50% mark. It's the basement that has high humidity.

I was hoping to have an ERV that can create positive pressure and bring in fresh air. I know when I open 1 window in the basement there is no more negative pressure even if I turn on all the exhaust fans and kitchen range to max speed. So I don't think I need much positive airflow for it to eventually balance out.

Also exchanging the air in the basement would reduce the radon levels even lower as an added benefit and reduce the stale air smell and bring in fresh air.
 
#6 ·
ERVs are balance flow. A home with adequate fresh air change will be damp evenings and rainy days when the a/c does not run enough. Most IAQ experts are recommending a fresh air change in 3-5 hours when occupied to purge indoor pollutants and renew oxygen. If you live in a green grass climate with moisture from the fresh air change and occupants requires 2-4 pints of dehumidification per hour during +60^F dew points evenings and rainy days. This will provide IAQ and comfort. These were lessons learned from COVID.

Keep us posted.

Regards Teddy Bear
 
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#10 ·
Even a foam house has many imperfections that allow air to leak in or out. Most will leak .1-.2 of an air change per hour in a 7 mph wind (considered an average winter wind) and stack effect. This is what keeps occupants of naturally ventilated home barely alive. In calm winds and no stack effect, natural infiltration declines to near zero and are not healthy spaces with accumulated pollutants and low oxygen.

A 2,000 sq.ft. home with 9' ceilings is 18,000 ft^3 of air volume. On a average winter day, these homes will leak 30-60 cfm of fresh air into and out of the inside space. During mild seasons with calm winds, fresh air change declines in response to the natural pressures.

Adding an ERV to these homes increases the air change rate of the home to the natural infiltration rate plus the mechanical balance air flow in/out of the ERV.

Adding a ventilating dehumidifier with make-up air effects in the air change rate of the same house by a lesser amount because the stale air must exfiltrate the home via the natural air leaks in home. The exfiltrating stale air slows or stops infiltration of fresh air depending on the size of the air leaks.

ASHRAE and AM. Medical Assn. suggest a fresh air change in 3-5 hours. An 2,000 sq.ft. home with a fresh change in 4 hours would be 75 cfm of fresh when occupied. Using 75 cfm of make-up Merv 13 filtered fresh air stop all of the unfiltered infiltrating fresh except when indoor exhaust devices (kitchen hood and clothes operated.

During colder winter conditions many home get enough infiltrating fresh air to not require mechanical fresh air. Monitoring the CO2 levels in the home will determine when the home is occupied and infiltrating fresh air is inadequate to purge indoor pollutants and need to renew oxygen.

For most homes, filtered make-up air is the most practical via a ventilating whole house dehumidifier like the Santa Fe Ultra, Broan, Trane, etc..

In defense of the ERV, it is certainly better than no mechanical fresh air ventilation. You will certianly need a whole house to maintain 50%RH during evenings and rainy days to remove the moisture that passes through the unit and moisture from the occupants. We test market a combo ERV and dehumidifier unit for the residential market. There was not enough payback to justify the investment.

Keep us posted.

Regards Teddy Bear
 
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T
#11 ·
Thank you for the detailed explanation.
My situation might be a little different, my 2nd and 1st floor humidity level is always around 50%. It is my basement that is 55-65%. It is always more humid in the basement than outside (except when it's raining) !!!
I'm worried if I install a whole home dehumidifier rule my 2nd and 1st floor will have humidity levels drop below 50%.
Also the ducting for each floor is completely separate and there is no way to link them up. I can potentially link up 1st and 2nd floor as both units are in the attic but the basement is in the mechanical room and there is no open chase. I know because I was trying to run another dedicated outlet last year.

So, back to your recommendation.
I have two "easy" options.
1) ERV for basement
2) Dehumidifier with fresh air inlet.

Note: The basement is enclosed by concrete and only 1 side has windows. So the natural infiltration is significantly reduced compared to 1st and 2nd floor.

1) ERV
Cons and Pros.
Pros = I can take air out of the mechanical room (unconditioned) and basement (conditioned) and add fresh air.
Pro 2 = It might increase the temperature of the basement in summer which will allow the Air Condition to run longer and dehumidify.
Con1 = Potentially I can increase the humidity in summer months but most ERVs have a humidity sensor that turns the ERV off if outdoor humidity is higher than a certain limit.
Con2 = More duct work needed

2) Dehumidifier with fresh air.
Pro = Much more efficient at Reduce humidity
Pro 2 = Will bring in fresh air
Cons = Any positive pressure in basement will have a hard time to escape and might choke the system as it won't be able to pull as much fresh air because of the higher pressure difference
Con2 = Won't exhaust that much stale are and might open windows (back to square 1)
 
T
#14 ·
Thank you Teddy Bear!

To answer your question > Where is the utility room getting the air from?
It's not! It's DEAD air inside.... I just enclosed the mechanical/utility room in a yellow box. 3/4 of the walls are concrete and the walls facing the condition space is almost air tight to conditioned space. The assembly from conditioned to mechanical room is Drywall on Vapor Barrier, R13 insulation, Vapor Barrier in a 2x4 stud. The door in a solid door (4hr fire rated) and has gaskets on all 4 sides making a seal.
I've put my phone playing music inside the room and closed the door.. it's sound proof. So I'm pretty sure it's air tight inside there and the smell is stale. I had to put a dedicated dehumidifier (Frigidaire 70) to keep that room at 50%.

So part of the ERV's advantage is I can suck air out of that mechanical room and replace it with fresh air. Have 4 exhausts, 2 in closets (conditioned) and 2 on each side of the mechanical room. Then two fresh air inlets one in the mechanical room and other into the HVAC unit.


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#16 ·
The concept is that you need a fresh air change throughout your home 3-5 hours when the home is occupied with a steady flow to purge indoor pollutants and renew oxyen. When the wind blows and it is cold outside, the stack effect and +10 mph winds, your home gets this level of ventilation naturally. When winds are calm and stack effect declines, your natural infiltration declines to near zero. Fresh air change is from opening doors, operation of the cloths drier, kitchen hood, and bath fans.

How does sucking air from your utility room and supplying fresh air to the utility room supply a steady flow of filtered fresh air through the home? Also you realize that ventilating your utility room with an ERV will make the room humid like the outside after about 3-4 air changes. ERVs do partially reduce moisture partially, if you exhaust 50%RH air. After one air change, the indoor %RH rises. The moisture transfer decreases to about half. The next air change has the reduction effect again. You need supplemental dehumidification to maintain 50%RH in the space to get the initial effect.

Your a/c will maintain 50%RH during days while there significant sensible loads by removing 2-9 lbs. per hour. Evenings and rainy days you, you need 2-6 lbs. per hour of supplemental dehumidification to maintain 50%RH through out the home. How does the utility room concept do this?

Reducing the negative pressure in this home is important to reduce sucking in soil gas which contains radon. Hope there are no open combustion devices in the home. Using a make-up air ventilation will reduce the negative pressure in the basement.

Keep us posted.

Regards Teddy Bear
 
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T
#17 ·
Sooo, I had an HVAC company come to look at options.

They said if I decide to do a Dehumidifier with Fresh Air for the basement. That would solve the negative pressure since it will equalize and dehumidify the basement. The issue is the utility room won't be connected to that since it's not in the conditioned space. They said you'd need an ERV in the utility room since the room above is my office and the if I do have a Radon issue (They don't have equipment to measure) it will go UP into my office which I'm there 8hrs a day... they said your only other options are Spray Foam the ceiling or make the utility room a conditioned space by adding a vapor barrier and link up your HVAC system to this side... They looked and said well my HVAC is oversized its 1.5TON and the conditioned space is only 650sqft. Soo linking to unconditioned space will bring it up to 1050sqft which would make it balanced...

ehhhh the costs are just going up up up up.

They referred me to a general contractor to get pricing on making the utility room conditioned...


Hmmmmmmmmmmmmmmmmmm
 
#18 ·
A couple more suggestions.
Using a whole house dehumidifier with a 6" dampered make-up fresh air duct and a a 10" dampered return from the main floor connected to the dehumidifier return, through a Merv 13 air. The dehumidifier supply is connected to the basement a/c supply duct. In addition a 6" duct with a balancing damper from the dehumidifier supply to the utility room. The damper in the 6" supply from the dehumidifier provides enough air to provide a slight positive pressure and humidity control in the utility room. The dehumidifier fan would operate 24/7 to control the radon in the utility room. A dehumidistat would be located in the finished basement and on the main floor to maintain 50% RH.
The dampered 6" dehumidifier supply can be adjusted to get enough fresh/house air to reduce radon and avoid high humidity in the utility area. The most of the dehumidifier supply will circulate the basement and then migrate through the floor and door undercut back to main floor. z

In case the radon is not controlled by this, suggest a radon fan be connected through the utility floor to maintain a strong negative pressure under the basement slab.

All of the suggestions used must be followed by radon and CO2 testing for to confirm the level of radon and fresh air change in the home. Most suggest a fresh air change in 3-5 hours to purge indoor pollutants and renew oxygen. Check local codes for acceptable radon levels.

YOur thoughts. Keep us posted on what you do and how it works.

Regards Teddy Bear
 
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T
#20 ·
Thank you Teddy Bear.

So there is no way to connect main floor to basement. The main floor and 2nd floor ducting all go up to the attic. There is no chase or opening to go from main floor to basement.
With that in mind, what would be your recommendation?
 
#21 ·
OK.

Dehumidifier in the utility room. Connect open part of the basement to the dehumidifier return along with a 6" dampered fresh air duct. Connect dehumidifier supply to the basement a/c supply duct. Also a 6" dampered from dehumidifier to the utility room. Bring in a fresh air change in 4 hours.

Run dehumidifier fan when home occupied. This will pressurize the utility room and basement the basement air being forced through the basement door undercut and through floor up through the main and second floor of the home. pressurize the all space with a fresh air change in 4 hours.

You giving up more mixing of main floor mixing with basement air. You are getting fresh air change and humidity control throughout.

It will work.

Keep us posted.

Regards Teddy Bear
 
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T
#22 ·
I had an HVAC company take a look for a quote.

They said I will need 2x Dehumidifiers with fresh air intake and 2x ERVs. The said as a basement the HVAC unit will run for very short periods of time which they showed me on my nest history report. So even if the air is conditioned it will still be stale and smell bad. They did not want to link up the unconditioned with conditioned space because the walls of the unconditioned space is concrete and they said they can't risk cross contamination... it's a liability thing..
They quote was 4x more than i expected lol

I asked if I could get an 1 ERV for both conditioned and unconditioned space. Then keep the Frigidaire dehumidifier 70 pint in the unconditioned space and add a dedicated humidifier connected to the HVAC unit. They said that would work but they can't do it...

The hunt continues
 
T
#23 ·
Update.
I had a Radon Specialist come and said my issue is I have a negative pressure in the basement which is letting radon come into all the cracks. It's at a low level so he said it's not necessary to add a mitigation system and said it wouldn't be that helpful as he needs to create a higher negative pressure under the slab to pull the Radon but it will also pull some air from your basement causing it to be more negative. So the Radon fan might have to operating at max speed.
Did a test with a Radon Monitor, 3 Tests for 3 days each. 1) As-Is Windows Closed. 2) Test again with 1 window cracked open. 3) Installed a small fan in a window running on low speed

The results were shocking.

3.5pCi/L - Windows Closed
2.2pCi/L - 1 Window 1/10th open
0.7pCi/L - Fan creating a positive pressure.

He recommend I get an ERV and create a positive pressure.


Soooooo time for the hunt for an ERV solution.

I was looking at the Panasonic FV-10VE2 but I do not see it having a humidity sensor. I want a system that would shut off if it's raining outside...
So I'm looking at the Broan - B150E75NT - 150 CFM AI Series Energy Recovery Ventilator w/ Top Ports (75% Efficiency). With the Advanced Touchscreen Control VTTOUCHW. It looks like it has an "AI" that would adjust the speed according to humidity but I don't know if I can force it to do a positive pressure.

Any recommendations on ERVs?
 
#24 ·
An ERV is a balance flow air exchange. How does that cause a positive pressure. So no negative pressure and the air exchange will make the space whatever the outside is.

Good Luck!

Keep us posted on how it works.

Regards Teddy Bear
 
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