Is this a PLENUM area I think so.

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mtnelect said:
You are correct ! ... The return would pull air in and the supply air would push air out of the structure.
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Only if that return chase had leaks to the outside, and even then it would slightly overpressure the building. Leaks internal to the building in a return i dont see as an issue and may even reduce static pressure. Supply leaks within the structure aren't as good, but they are still leaking in conditioned space. If supply is leaking to the outside air, that isnt efficient.
 
I have thought of adding a screened outside-air inlet and insulated duct to my return duct, to create a positive pressure inside. I have wired actuators for this in commercial-building HVAC systems for the same reason.

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That way, exhaust fans, the clothes dryer, gas-appliance flues, and any leaks would not be as inclined to pull un-conditioned air in, and instead, outside air would be mixed with inside air before being released inside.
 
mtnelect said:
As for the NEC is concerned with, it is control wiring for HVAC. But for using building structures as return air, it is the California Energy Commission requirements under Title 24, that forbids it.
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So most what you said only applies in CA?

They are still using space between studs or floor joists for return air pretty often around here. As the EC and with NEC as my rule book it kind of isn't my problem that they are doing it, but does effect what or how I can run within such spaces when present
 
mtnelect said:
Yes ... It's because of the CEC Title 24. California doesn't want to build anymore power plants. They want residential structures to be "Airtight", and by using building structures as air returns, air can leak out.
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Leak out of what? The return should have negative pressure. Worst you are going to do is pull additional air from other than where the inlet is. If you haven't sufficiently sized your return system you get that anyway if you don't have a well enough sealed system.
 
kwired said:
So most what you said only applies in CA?

They are still using space between studs or floor joists for return air pretty often around here. As the EC and with NEC as my rule book it kind of isn't my problem that they are doing it, but does effect what or how I can run within such spaces when present
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You are correct ! ... This only applies to California.
 
This attachment explains the uphill battle California is having to achieve energy efficiency even with the requirements of Title 24.
 

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  • IHACI - Comments.pdf
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jxofaltrds said:
I find this problem almost every day in Ohio. The other day a return caused half of the 1st floor to 'act' as the plenum.

View attachment 2560172
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What is reason for such construction and why do you run into it almost every day. Looks to me like something I might only find on occasion.

Why such a thick wall cavity is my main question, or are they trying to create a larger "duct"? but if so why isn't more of the floor cut out?
 
May be other states will realize that we don't have unlimited energy to waste ... May be building more power plants isn't the answer !
 
Depends on what you mean by waisted energy, can’t be green when slave labor in polluting China is making are panels.
mtnelect said:
May be other states will realize that we don't have unlimited energy to waste ... May be building more power plants isn't the answer
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thanks for the info by the way inspector was surprised never seen this setup before in a home
 
California with Title 24 has decided to take a second look at how we construct our buildings. I hope we all can contribute to this process to make our nation more energy efficient.
 
mtnelect said:
California with Title 24 has decided to take a second look at how we construct our buildings. I hope we all can contribute to this process to make our nation more energy efficient.
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I have a problem with the "you must" approach, we are supposed to be a free country.

I have no problem with some incentives that make doing it a certain way the one that ultimately is likely to be chosen, not just talking about monetary rewards either. You can't buy certain things anymore unless you get an older used model, this because newer ones have been made to operate more efficiently.

Older AC units still around here, but is getting to point that if they need (R22) refrigerant it has gotten expensive enough to add refrigerant that it does make sense to upgrade to a newer and more efficient unit. Somewhat no law saying they must do that, yet it is what makes most sense to do and is somewhat indirectly because of other laws that ended up driving the R22 price to where it is.

Sadly some older people that have limited funds will likely stop using their AC if it comes to needing to make a decision like this. If anything they maybe purchase a window or other portable style unit and though it may be more efficient than older window units still isn't as efficient as many new central units will be overall.
 
kwired said:
I have a problem with the "you must" approach, we are supposed to be a free country.

I have no problem with some incentives that make doing it a certain way the one that ultimately is likely to be chosen, not just talking about monetary rewards either. You can't buy certain things anymore unless you get an older used model, this because newer ones have been made to operate more efficiently.

Older AC units still around here, but is getting to point that if they need (R22) refrigerant it has gotten expensive enough to add refrigerant that it does make sense to upgrade to a newer and more efficient unit. Somewhat no law saying they must do that, yet it is what makes most sense to do and is somewhat indirectly because of other laws that ended up driving the R22 price to where it is.

Sadly some older people that have limited funds will likely stop using their AC if it comes to needing to make a decision like this. If anything they maybe purchase a window or other portable style unit and though it may be more efficient than older window units still isn't as efficient as many new central units will be overall.
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Thank you for your response ! ... I am a creature of habit, so it was hard for me to change from installing a ducted to a ductless HVAC system. When California started enforcing Title 24, the first thing I noticed was the HERS (Home Energy Rating System) inspection requirements were very restrictive. I started having trouble passing inspections. My ducting systems were leaking too much air, so I had to go back each time and make repairs to pass inspection. That's when I started to realize that a conventional forced air system was not energy efficient, especially ducting systems in attics exposed to outside temperatures. So, I decided to change to ductless Heat Pumps.

Please see attachment.
 

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  • Public Comments - Heat Pump.pdf
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mtnelect said:
Thank you for your response ! ... I am a creature of habit, so it was hard for me to change from installing a ducted to a ductless HVAC system. When California started enforcing Title 24, the first thing I noticed was the HERS (Home Energy Rating System) inspection requirements were very restrictive. I started having trouble passing inspections. My ducting systems were leaking too much air, so I had to go back each time and make repairs to pass inspection. That's when I started to realize that a conventional forced air system was not energy efficient, especially ducting systems in attics exposed to outside temperatures. So, I decided to change to ductless Heat Pumps.

Please see attachment.
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A lot of homes likely constructed differently where you are than where I am and factors into this some as well.

Not that there isn't any ducts run in attics or crawl spaces here, but many more homes do have a basement or multi-levels and ducting is run within the space being conditioned, those losses in the conditioned space are not intended design, but aren't exactly lost if it ends up in the conditioned space either. I don't know if you ever been around some old coal fired boiler systems that had a natural gas burner conversion added to them, they make the efficiency of many 1960's forced air gas furnaces look pretty good let alone how much more efficient a a modern gas burning furnace or boiler is.

Then a problem you don't really have in most of CA is does your super efficient heat pump still work very well when it gets really cold out, like below zero deg F? They have gotten better over the years, but they still don't move as much heat when it is that cold as when it is say ~50F outside.
 
kwired said:
A lot of homes likely constructed differently where you are than where I am and factors into this some as well.

Not that there isn't any ducts run in attics or crawl spaces here, but many more homes do have a basement or multi-levels and ducting is run within the space being conditioned, those losses in the conditioned space are not intended design, but aren't exactly lost if it ends up in the conditioned space either. I don't know if you ever been around some old coal fired boiler systems that had a natural gas burner conversion added to them, they make the efficiency of many 1960's forced air gas furnaces look pretty good let alone how much more efficient a a modern gas burning furnace or boiler is.

Then a problem you don't really have in most of CA is does your super efficient heat pump still work very well when it gets really cold out, like below zero deg F? They have gotten better over the years, but they still don't move as much heat when it is that cold as when it is say ~50F outside.
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The 50 degree is true for ducted Heat Pumps that usually have auxiliary heat, but ductless Mini Splits can operate down to 20 degrees, with no auxiliary heat is required. The only problem with ductless is when the outside temperature gets below 35 degrees it will sense ice build-up and go into "Defrost" mode to melt the ice for 15 minutes.
 
mtnelect said:
The 50 degree is true for ducted Heat Pumps that usually have auxiliary heat, but ductless Mini Splits can operate down to 20 degrees, with no auxiliary heat is required. The only problem with ductless is when the outside temperature gets below 35 degrees it will sense ice build-up and go into "Defrost" mode to melt the ice for 15 minutes.
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We have places using ductless with no backup heat or if there is other heat it is not associated with the ductless system in any way - often just spill over heat from an adjacent area at best. And we get to zero and below every winter, usually not for more than a few days at a time, but is still cold enough that those systems would still be needing to operate, and for the most part they do.

All air to air heat pumps you see here, ductless or not, have defrost function of some sort, they simply don't work if the outdoor coil is plugged with ice.
 
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