ERV Retrofit Wall Supply Points and Insulation
Looking at installing a ventilation system with dedicated supply and return ducting in a Zone 5 ranch with a basement.
The system supply/exhaust I know will be insulated.
It seems that returns can be uninsulated (though a return in a hot steamy shower concerns me).
My question is primarily related to the non-system supplies. I don’t have any viable chases to the attic for ceiling registers. My current plan is to open interior walls and use what space is available coming up from the basement. Alternatives would be floor registers or tying to the forced-air system if necessary (trading one concern for another).
I’m probably way overthinking/over-worrying about this but:
Are wall ducts a cause of concern for condensation -> mold?
Should these supplies be insulated within a wall?
Is condensation (inside or outside the duct) within a wall an actual concern for ventilation ducting?
It seems the best way to use a 2×4 wall for ducting is with a wall stack, and the typical sizes use the entire stud space leaving no space for insulation.
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Replies
Seem to me your house is very very unlikely to need this system.
Have you received a blower door test report under 0.75 ACH50?
Do you have excessive indoor humidity in the heating season?
Without one of the above I say this equipment is a solution in search of a problem.
I say it is next to impossible to seal up an existing building tight enough to require this equipment.
Spend your money on insulation and air sealing.
Walta
The indoor air quality in almost every house will benefit from mechanical ventilation. It may not be required by codes, or desired by everyone, but if you monitor your interior air conditions, you'll see an improvement with ventilation.
Ventilation ductwork is rarely insulated, except for the ducts from the machine to the exterior. You shouldn't use the framing cavities as plenums but sheet metal ducting and wall stacks will work fine.
You can also get Zehnder Comfotubes which are made for this purpose; Zehnder would prefer you buy their equipment as well but at least as of a few years ago you could order Comfotubes alone. They are relatively expensive so if you can do it with sheet metal, or have someone who can, that will probably be the least expensive option.
I should add that I'm talking about balanced ventilation systems, where the air on the indoor side of the machine will be relatively close to room temperature. If you're talking about supply-only ventilation, without preheaters, the incoming air would be cold enough to be a problem. But ERV supply air is usually well above dewpoint temperatures and not a cause for concern. If the incoming air will be below the dewpoint temperature, the best solution is to heat the incoming air.
Walta,
While I have not had a blower door test performed, I agree that my late-1990s house is no where near 1 ACH 50 or below. I did some attic air sealing and insulation already. Foaming the basement is next.
Michael hit the nail that my desire for a ventilation system is for better indoor air quality and house comfort control.
Then it becomes 'how to implement correctly without causing problems'.
The unit I am looking at can provide constant recirculation in addition to ventilation.
Michael,
Agreed, sheet metal ducting and not just through the cavity.
I did see that Comfotubes were available. I couldn't find the exact page I saw the other day, but it might have to be ComfoFlex as there is a possible code issue for Comfotubes not being UL listed (older article but possibly still relevant: https://www.greenbuildingadvisor.com/question/zehnder-comfotube-code-issue)
Still probably a more DIY option in tight spaces.
> But ERV supply air is usually well above dewpoint temperatures and not a cause for concern. If the incoming air will be below the dewpoint temperature, the best solution is to heat the incoming air.
I was given a rough calculation that at 10 F outside and 68 F inside the supply air would "likely be in the 50's". I'm in a much better position to track my indoor conditions and averaged 36% RH at 68/69 F indoors last year during average winter temperatures (dew points around 40). Maybe I should just be comfortable enough with this 10ish degree gap.
I'll look into the option of a preheater and see how it integrates. Much appreciated for the idea! I suppose I could also just turn the system off when we get a polar vortex again (-15 F or so) instead of worrying about a system that functions in the entire range of possible temperatures.
I had actually written that supply air would likely be no lower than the 50s but decided to keep it more vague ;-)
I know a lot of pros who like using Comfotubes because of their simplicity and ease of installation. It's something that carpenters can do. I like working with sheet metal but most carpenters do not, and HVAC tin knockers are in short supply. If you're up for it, you can get your own pre-formed rectangular ducts at supply houses or big box stores. I get my stuff from Homan Supply when I can; they have many locations in the northeast US if that's where you are.
Mold doesn't take hold immediately so a few days with supply air below the dewpoint won't be a major issue, but for comfort reasons you might want the preheater anyway. The more efficient the unit, the higher the supply air temperature.