Let’s talk home ventilation and indoor air quality, Hearth.com style.

[EbS-P]

I have spent lots of time leaning about residential HVAC. None of my research has led to anything building science related topics that includes solid fuel heating appliances.

new construction codes are requiring tighter construction and spray foam insulation is being more widely used. New homes are getting tighter annd better insulated and that is a good thing but comes with trade offs especially in humid climate.

It is recommended that you have 1 full air exchange in your home every 3-4 hours. Or 15 cfm per person.

How much ventilation do I need in my home to improve indoor air quality? | US EPA

The American Society of Heating, Refrigeration and Air-Conditioning Engineering (ASHRAE recommends (in its Standard 62-1999, "Ventilation for Acceptable Indoor Air Quality") that homes receive .35 air changes per hour, but not less than 15 cubic feet pe

www.epa.gov

so let’s lay out some basics. Every 1000 sq ft of home should have 33 cfm of ventilation.

Now come the important part where is this air coming from. Leaks? ERV/HRV? Ventilating dehumidifier?

With solid fuel appliances we know we need make up air. How much effort/concerned should we be about conditioning the incoming air?

I think in the coming years there will much more talk about fresh air ventilation for homes and how to best control and condition it. I am considering adding a fresh air ventilation to my whole home dehumidifier. It currently don’t have it.

What are your thoughts?

 

[zak77]

I think we're in for a lot of houses with mold/moisture problems and damages in the next decade or so. Bottling up a wood structure with no way for moisture to get out is just asking for lots of problems but that's just what newer building codes are producing. Plus, the materials being used are only making things worse and the vast majority of builders dont understand how to do things right or just dont care to do things right. Personally, i think ventilation is critical. I would really like to put in a HRV or ERV but they're not cheap so in the meantime i open windows daily in my house and turn on bathroom fans to exchange air. Not the best option but it's better than nothing. The Journal of Light Construction is always dealing with this issue and how to cure it, along with other interesting articles about houses.

 

[peakbagger]

Go onto You Tube and search for the BS and Beer shows. They cover Building Science in fairly understandable format. I just read a book by Allison Bailes " A House needs to breathe, Or Does It?. It covers the basics but not super in depth.

 

[stoveliker]

On the other side of the ocean where I'm from, places are much, much tighter than here - b/c brick homes, and far higher quality windows and doors (possibly because far stiffer construction due to no stick-built walls, so less flexing, gaps, etc.)

Either homes have (mechanical) ventilation systems, or they have moisture and mold problems. Either one of the two, no exceptions.

So yes, this is important.

 

[EbS-P]

Go onto You Tube and search for the BS and Beer shows. They cover Building Science in fairly understandable format. I just read a book by Allison Bailes " A House needs to breathe, Or Does It?. It covers the basics but not super in depth.

I keep meaning to read it. But at 70$ I’m not It buying it. I’ll check my library.

I have followed several podcasts that discuss the book.

I think we're in for a lot of houses with mold/moisture problems and damages in the next decade or so. Bottling up a wood structure with no way for moisture to get out is just asking for lots of problems but that's just what newer building codes are producing. Plus, the materials being used are only making things worse and the vast majority of builders dont understand how to do things right or just dont care to do things right. Personally, i think ventilation is critical. I would really like to put in a HRV or ERV but they're not cheap so in the meantime i open windows daily in my house and turn on bathroom fans to exchange air. Not the best option but it's better than nothing. The Journal of Light Construction is always dealing with this issue and how to cure it, along with other interesting articles about houses.

We had warm couple day’s yesterday where they were compelled burning pine plantations. Smoke was bad and the AC was off due to duct work. Humidity inside got over 70% at 80 degrees.

I’m landing on the singular but expensive while home dehumidifier that has a motorized damper connected to a 6” outdoor intake as the best solution for me. Humidity is super high here.

The hearth.com angle is what is the appropriate fresh air requirement when burning? And in the summer how much does a single flue contribute to the leakage rate? Should I be sealing my flies off in the summer?? The real answer is a blower door test.

But I haven’t had one done.

Where is geographic boundary where one should choose a ventilating dehumidifier? Where is an ERV a good choice? Where do HRVs belong?

Really how many even track indoor humidity?

 

[Prometeo]

a family member started by buying a value meter, discovered that using the extractor fan in the kitchen, sucked smoke from the flue, from the bathroom air intake, moreover, having no ventilation but strong insulation, the air quality was not very good, and is thinking about doing hvac

 

[bholler]

a family member started by buying a value meter, discovered that using the extractor fan in the kitchen, sucked smoke from the flue, from the bathroom air intake, moreover, having no ventilation but strong insulation, the air quality was not very good, and is thinking about doing hvac

Well yeah. In a tight home when you turn on one exhaust it's generally going to reverse through others

 

[ABMax24]

Radon is another factor to consider in this. I bought a digital detector a couple months back, and with the wood stove and furnace running periodically my levels were certainly higher than outside, but nothing to be alarmed about. Now that I'm not really using the wood stove or the furnace and its not yet warm enough to open windows during the day the Radon levels have tripled. I'm still below the action level in Canada, but I'm not happy with it.

 

[EbS-P]

Radon is another factor to consider in this. I bought a digital detector a couple months back, and with the wood stove and furnace running periodically my levels were certainly higher than outside, but nothing to be alarmed about. Now that I'm not really using the wood stove or the furnace and its not yet warm enough to open windows during the day the Radon levels have tripled. I'm still below the action level in Canada, but I'm not happy with it.

Radon ventilation for finished basements I think could be tricky in certain climates during the not heat shoulder season in terms of humidity control.

Portable dehumidifiers work. I was just done with the noise and bucket brigade. I am glad radon is not a concern here on the beach. My crawl space floor is 100% beach sand. (4 miles from the coast as the crow flies).

 

[EbS-P]

Without a blower door test is it a good idea add mechanical fresh air ventilation?

Should the stove flue(s) be sealed for the door test?

 

[zak77]

"Should the stove flue(s) be sealed for the door test?"

Yes. I've had my local utility company out to my house for adding insulation and every time they REALLY want to do a blower door test, since they get paid more for air sealing than insulation installation, but they told me i cant have my wood stove burning at the time. I've already air sealed my house to the point where i'm happy with it and i know these guys will want to seal every single nook and cranny, plus they do sloppy work. So both times, sorry guys wood stove's cranked up cant do a blower door test.

 

[Nate R]

It is recommended that you have 1 full air exchange in your home every 3-4 hours. Or 15 cfm per person.

I think in the coming years there will much more talk about fresh air ventilation for homes and how to best control and condition it. I am considering adding a fresh air ventilation to my whole home dehumidifier. It currently don’t have it.

What are your thoughts?

I side with Joe Lstiburek on this one....IIRC he thinks the recommendation is too high, and believes it should be about 1/2 of what it is.
I currently have no fresh air ventilation in my under-construction cabin... 520 SF or so. But am considering adding something, but not liking the small/single room stuff out there currently. Might make my own contraption with a computer fan, filter(s) and possible heating element optionally.

My primary home is a 100 yr old duplex. I had the walls insulated in the last couple years and resided with housewrap added. Tightened things up a lot, but still pretty leaky overall.... More than anything I need to add exhaust ventilation in that home.

I do monitor Interior RH in both structures.... Cabin is getting a seasonal dehumidifier added, and the main house has one on the basement, and central air....which combined has kept RH reasonable, despite my wife's plants. :-D

 

[EbS-P]

I have been tracking CO2. We are a family of 7 spending most of the time in the 2000 sq ft up stairs. I am guessing that most of my natural ventilation (leakage) is in the basement.

CO2 this morning when we woke up on the far side of the house from the bedrooms (upstairs) was 950 ppm. The old leaky ductwork that has been completely replaced has now corrected the negative pressure leakage.

At what level CO2 levels would you start bringing more fresh air in??

 

[Nate R]

I have been tracking CO2. We are a family of 7 spending most of the time in the 2000 sq ft up stairs. I am guessing that most of my natural ventilation (leakage) is in the basement.

CO2 this morning when we woke up on the far side of the house from the bedrooms (upstairs) was 950 ppm. The old leaky ductwork that has been completely replaced has now corrected the negative pressure leakage.

At what level CO2 levels would you start bringing more fresh air in??

I've seen people say between 1000 and up to 1500 before you really should consider bringing in fresh air.

 

[Poindexter]

Late to the party, sorry, new job.

My next home, at 65 north, is going to have a wood stove, AC and an ERV.

My immediate plan is to have a switch near the wood stove so I can turn the ERV off when the loading door of the wood stove is open. In that scenario the woodstove will have an independent air intake, an OAK, so I not feeding conditioned air to the stove as air intake.

There are many youtubes free from the BS and beer crowd, but they get cumbersome quick with more than 4 participants or so.

I think tight(er) homes are here to stay, but there is some planning required.

 

[stoveliker]

My immediate plan is to have a switch near the wood stove so I can turn the ERV off when the loading door of the wood stove is open. In that scenario the woodstove will have an independent air intake, an OAK, so I not feeding conditioned air to the stove as air intake.

If you have a negative pressure in your stove room, you'll be equalizing that with air from your (oak and) stove the moment you open the door...?

 

[EbS-P]

Late to the party, sorry, new job.

My next home, at 65 north, is going to have a wood stove, AC and an ERV.

My immediate plan is to have a switch near the wood stove so I can turn the ERV off when the loading door of the wood stove is open. In that scenario the woodstove will have an independent air intake, an OAK, so I not feeding conditioned air to the stove as air intake.

There are many youtubes free from the BS and beer crowd, but they get cumbersome quick with more than 4 participants or so.

I think tight(er) homes are here to stay, but there is some planning required.

In a tight house I would always want slight positive pressure. An HRV or ERV with variable intake and exhaust adjustments would be a requirement for me.

I haven’t been collecting co2 data. Just reading off my monitor. Humidity I have been tracking. It’s shoulder season here. Going from AC to heat in the span of a couple days. Re acclimation to heat and humidity takes time. Getting used to cold and dry just happens.

Indoor cooking has magnitudes more negative effect on indoor air quality than wood stoves. We don’t have a range hood. Any large range hood with new tight construction needs be counted to some outside air intake preferably conditioned outside air and at least filtered. A 400 cfm hood moves a lot of air.

Down south a ventilating dehumidifier might be a good choice. But making up 400 cfm in a house that is 1.5 ACH50 is huge.

 

[Poindexter]

Whether a tight home should be slight negative, slight positive or neutral pressure I am not equipped to offer an informed opinion.

At all the hospitals where I have worked that I noticed, they had slight positive pressure. The UNC system Marine Science lab, I think it might be in Wilmington, was designed with positive pressure to keep salt air off the expensive lab gear. If it is still standing the building I am thinking of is probably at least 40 years old. It might be in Beaufort.

In wild fire season up here I would want slight positive pressure inside my house to minimize smoke intrusion when the doors are opened.

Otherwise I got nothing and look forward to learning from those of you farther down the road than I am.

 

[ABMax24]

Slight positive pressure helps with minimize Radon infiltration.

However, in a 3 story house like mine the basement is generally in negative pressure anyway due to the stack effect most of the year, with warm air constantly escaping the upstairs bathroom vents. Pressurizing the house would make this heat loss worse.

 

[EbS-P]

whole house dehumidifier is running. 36 hours now no AC until just now. I’m finding my humidistat I looked last summer may have been miss calibrated by reading 6-8% low.

I’m also finding that a big family, where the house is never empty, probably has much different ventilation requirements.

And I really think any actionable discussion must either pick retrofit or new construction…. Better yet house volume, AHC 50 #, and monthly average dew point. Did I miss anything there? Oh how much you want to spend to achieve your desired comfort level.

So here is the reasonably calibrated data since the dehumidifier was turned on. For reference it’s a Santa Fe Oasis 105. It was not cheap. We can go into the reasons I chose it later, I have thoughts and have second thoughts but that’s for later. The unit is connected to my Ecobee premium thermostat. More thoughts on that later. But it’s working fine.

Data is from my Govee logger.

The house just feels better. The unit pulls 500w. I figure 15-20$ a month in electricity. Or 3 of my wifes Starbucks drinks. And once we get warmer weather that cost will go down as the AC takes over the dehumidification role. But it really can’t keep up when it’s really humid out, as I found out last summer.

 

[EbS-P]

This could possibly be its own thread but, I want it here for now.

My research has shown no smart thermostats capable of controlling a ventilating dehumidifier. This issue is that three things need to be controlled. Fan for fresh air ventilation, compressor (and this the fan) for dehumidification. And the fresh air damper. Now there are controllers that can control these functions sold by the dehumidifier manufacturers but they do not monitor indoor air quality and they are expensive.

One could set up a co2 controller to open the fresh air damper and turn on the fan. But a a separate humidity sensor would have to be added offer the the fresh air intake (probably right at the dehumidifier) to then send control the dehumidifier.

I’m a bit miffed that a smart integrated controller does not exist that is diy friendly.

Any way the takeaway is don’t expect a single controller to be able to be connected to the internet, run your hvac, dehumidifier, fresh air ventilation and monitor indoor air quality.

 

[gthomas785]

There are commercial ones that can do that, I'm thinking something like a jade economizer controller with CO2 and enthalpy sensors, but they are pricey.

 

[EbS-P]

There are commercial ones that can do that, I'm thinking something like a jade economizer controller with CO2 and enthalpy sensors, but they are pricey.

I looked up the jade unit. The actual unit and actuator probably are not that much more expensive than what the dehumidifier manufacturers are selling. But if you need a 400$ in duct co2 sensor, the whole control package is probably $1000-1200.

 

[gthomas785]

I looked up the jade unit. The actual unit and actuator probably are not that much more expensive than what the dehumidifier manufacturers are selling. But if you need a 400$ in duct co2 sensor, the whole control package is probably $1000-1200.

Yeah that's what I meant by pricey. Not worth it for the average homeowner application unless you absolutely love to play with this stuff.

 

[ABMax24]

The crappy thing is a device like the Ecobee could easily perform so many custom functions if they let the end user write a few lines of code within the device.

I have the same frustration, I want the Ecobee to cycle the furnace fan when there is a significant temperature differential between areas of the house. Can't do that without another standalone system device to read the Ecobee sensors, process the data, and then tell the Ecobee to turn the fan on.

My Ecobee is an expensive wall ornament.