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fresh air intake into cold air return

Will92's picture

Greetings everyone:


I am looking at new 80% furnaces.  I heard about new air quality recommendations towards increasing fresh air intake into HVAC systems.  I have looked into ERV and HRV but I was discouraged from tying them into the existing HVAC system and that it would be better if they had their own dedicated duct work.  Therefore, I found another potential alternative I want to run by the group.  It is a motorized, dampered fresh air intake made by Honeywell.  A penetration to an outside wall is obviously needed and when there is a call for heat or cold, the damper will open and fresh air will correspondingly be drawn into the cold air return of the furnace.  I think it can also be programmed to open as specified intervals (when one is using a furnace with variable speed motor and the fan is recirculating the air constantly).  I realize that this puts a slight load on the furnace or AC since in winter one is dumping cold air in the air return return and during summer one is dumping hot air into the cold air return.  However, the device is much cheaper than an ERV or HRV.


Does anyone have input on using a device like this?  I would have the furnace company install it as part of the job.


Here is a description of the unit:


http://www.zonecontrolblog.com/the_zone_control_blog/2008/10/honeywell-8150.html


Thank you.


Edited 11/6/2008 11:40 pm ET by Will92


Edited 11/6/2008 11:42 pm ET by Will92

(post #115478, reply #1 of 73)

I can remember doing this 25 or so years ago w/o the damper.  The purpose was to prevent backdrafting of gravity vent furnaces.  It was also done to prevent the structure from going "negative" and was often part of a radon mitigation process.


I don't know your location but the real benefit of the damper is probably in the summer if you have humidity issues at that time with airconditioning.  Whenever a gravity vent burner is firing, there must be a source of air to replace the air going up the chimney.  You would be providing a source from the whole house instead of the furnace room where the burner is located. 


In years past, before buildings became sealed and insulated, this air came from around the doors, windows, lights, outlets and other openings. 


Sending the air into the RA of the furnace allows the air to also be used to replace exhaust air such as bath fans, range hoods, fireplaces, etc. provided that the damper is open.  The thing to remember, is that any air exhausted or vented, from a building will be replaced.  In the intrest of energy conservation, it is best to control this in some way.  They tell the siding guys to think like water, you need to think like air.


Chris

(post #115478, reply #4 of 73)

The purpose was to prevent backdrafting of gravity vent furnaces.  It was also done to prevent the structure from going "negative" and was often part of a radon mitigation process.


I disagree. When you put ventilation air into the return air, it is not for combustion air ... that should be a separate inlet ... and is actually required in certain situations. The fresh air intake being referred to will not prevent backdrafting if the furnace is in a tight room ... this assumes of course that the OP meant to connect the vent duct/damper to the return air of the furnace.


Never heard of this strategy for radon. Radon mitigation normally occurs sub slab w/ negative pressure system, not with ventilation air. Certainly ventilation will lower radon levels, but that is not the way to mitigate radon.

There ain't NO free lunch. Not no how, not no where!

(post #115478, reply #5 of 73)

The basic idea is to provide positive pressure in the house. This prevents back-drafting on any open combustion appliances (or from leaks in closed combustion appliances), helps with radon mitigation, and eliminates drafts from minor air leaks through the building envelope. In addition, of course, it provides a positive way to achieve air changes in the structure.


Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115478, reply #16 of 73)

It will only provide backdraft prevention if it is actually on when the appliance fires up. So if it is not interconnected, you can't rely on it to provide that function and certainly not for the furnace it is connected to, as many are in a "confined space" and would require separate combustion air anyway.


As I indicated in another posting ... ventilation is no way to mitigate radon. You'd have to have it on 24/7.


The only purpose that it has ... is your last reason:  ventilation air, air changes, fresh air to replace stale, overly moist, odors, or otherwise polluted air that is exhausted or otherwise unwanted.

There ain't NO free lunch. Not no how, not no where!

(post #115478, reply #25 of 73)

>>ventilation is no way to mitigate radon.

Mitigating radon isn't what we're discussing - we're talking about "mitigating" to a degree conditions which contribute to higher radon levels in the home.





"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115478, reply #28 of 73)

>>[A return air supply] It will only provide backdraft prevention if it is actually on when the appliance fires up.

Why do you think that?

Are you thinking that the flow or air in a proporly drafting gas appliance can't be reversed?

Stick a draft gauge in a flue -fire the unit up and then traverse the house turning on ventilation fans -- it doesn't happen mcuh, but I've done plenty of testing where a properly drafting appliance went negative in that sort of testing.





"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115478, reply #39 of 73)

The set up mentioned would not put a positive pressure on the house. A fan would have to be added inline to accomplish that. Since he is only using the normal blower in the furnace, the system would only intake fresh air as a result. The guys question seems to have been forgotten though. "Will this replace an ERV or HRV?". The answer to that question is simply no. The HRV can pre-heat the fresh air being dumped into the return plenum of the furnace with heat energy pulled out of the houses stale/humid exhaust air.

(post #115478, reply #43 of 73)

It will too create positive pressure. Think about it.


The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115478, reply #45 of 73)

No it will not. The furnace has return air ducts throughout the house. These return air ducts are the primary source of air for the blower in the furnace. (Picture a circle here) The only time you would conceivably pressurize the house by adding a 3" fresh air intake is if the return air system is not balanced with the supply side, the furnace would then make up the air from outside. Now I will give up the fact that a lot of forced hot air systems are in fact not balanced properly and therefore could in fact lead to the condition, but the system in question can not be marketed or used in that fashion. Side note, the draft on most fuel burning appliance is designed to go up the chimney at or near atmospheric pressure, pressurizing a house with a natural draft appliance such as a conventional gas furnace, could in fact cause the appliance to burn or draft improperly.


Edited 11/11/2008 8:18 pm ET by losh

(post #115478, reply #46 of 73)

Will too!


The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115478, reply #48 of 73)

Dan,  The only time this could happen is from the venturi effect of air passing by the fresh air inlet.  Is this what you are referring to??


I haven't installed a scorched air furnace in a home in 25 years.  In homes without a ducting system, these systems do nothing but prevent a negative pressure situation in the house.


The only time air ever passes through them is when it actually is needed as makeup air and that will never cause positive pressure in a home.

(post #115478, reply #49 of 73)

No.

And I'm referring to a standard forced air system with full supply and return duct systems, the more balanced the better.

A duct leading from outside to the return air plenum will produce a slight positive pressure in the house.


The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115478, reply #54 of 73)

Yes,  that's what meant.  Only when the fan is running.  The problem is that there are so many variables in controlling how much air actually enters the house...and that's where the problems start.

(post #115478, reply #55 of 73)

There may be problems, but a positive pressure is produced.


The only function of economic forecasting is to make astrology look respectable. --John Kenneth Galbraith


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115478, reply #9 of 73)

>>Never heard of this strategy for radon. Radon mitigation normally occurs sub slab w/ negative pressure system, not with ventilation air. Certainly ventilation will lower radon levels, but that is not the way to mitigate radon.

Radon levels can be increased by the negative pressure zone that naturally occurs in a basement, and, given the lack of good return sealing adding such a supply can help reduce the negative pressure in the basement.





"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115478, reply #15 of 73)

You are right ... negative pressure can have a tendency to increase radon levels ... but I've never heard of mitigating it with ventilation air. I've had a lot of training in radon and worked with a number of mitigation systems and NEVER heard of anyone ever suggesting mitigation through ventilation. While ventilating may mitigate, that means you would have to overventilate ... as you would have to do it 24/7.

There ain't NO free lunch. Not no how, not no where!

(post #115478, reply #24 of 73)

I believe the state of Ohio includes this as one mitigation technique.

And don't forget, the low pressure is caused, in part, by the gas appliances in that zone, and, I believe, is seasonally on the same cycle as when we use our gas appliances most





"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115478, reply #30 of 73)

You're kidding, right. I'm guessing the state of Ohio knows zip about radon mitigation if that is the case. Maybe this would be true if the system guaranteed 24/7 ventilation ... which would be taking this discussion out of context. Even so, that is likely a poor strategy to use as it would be energy intensive (ventilating and using the larger furnace fan to do it).


Your second statement doesn't make any sense to me (I'm say I have no idea what you are trying to say).


Edited 11/8/2008 10:05 am ET by Clewless1


Edited 11/8/2008 10:06 am ET by Clewless1

There ain't NO free lunch. Not no how, not no where!

(post #115478, reply #17 of 73)

Seems it would be easier/better to seal your return, then. Ventilation is not mitigation. I think any radon expert would laugh at using ventilation for mitigation. I'd hate to see the OP walk away w/ the notion that it might improve his radon outlook ... or any other reader getting some ideas for himself. While your notion has theoretical merit ... the practicality of it is just not there. Sorry to oppose this, but anyone planning to mitigate radon this way would be making a mistake, I think. I'd rather take up smoking and take my chances than rely on occasional/intermitent ventilation to mitigate a radon problem.

There ain't NO free lunch. Not no how, not no where!

(post #115478, reply #26 of 73)

>>Seems it would be easier/better to seal your return, then.

Ever try sealing a panned joist bay return?

>>Ventilation is not mitigation.

You're right, but as noted, that's not what we're discussing.





"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115478, reply #32 of 73)

If the panned bay is accessible ... should be relatively easy to seal. Pull the pan off and have at it. Then seal the pan when reinstalling.


I thought there was clear implication that your statement was one of mitigating radon. You imply by supplying ventilation that the condition for higher levels of radon are minimized ... sounds like intended mitigation strategy to me. I understand what you are saying, but you can't eliminate the condition a small percentage of the time and then call it good (i.e. the condition for higher radon levels is now gone 'all the time'). It's like ventilating a smoke filled room for short periods and declaring it good to occupy all the time. While I or you may CHOOSE to expose ourselves to negative conditions for whatever periods of time, you really can't imply that you can rely on this approach to control the condition.

There ain't NO free lunch. Not no how, not no where!

(post #115478, reply #35 of 73)

>>If the panned bay is accessible ... should be relatively easy to seal. Pull the pan off and have at it. Then seal the pan when reinstalling.

Easy in theory, a bit tougher in practice, in my experience.

Sorry if I misspoke on the radon side of things - minor "mitigation" of the radon effects of negative pressure in the lowest level of a house is merely one minor part of the effects of such a systems- it is no way intended to be a significant system or approach to deal with radon issues.

Sorry I wasn't clear on that.





"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115478, reply #36 of 73)

Yeah ... its practical applications that can make or break a 'simple concept' (referring to the pan joist duct return).


No prob ... just trying to round out the discussion since the radon thing was brought up ... didn't want widespread confusion to result in widespread rumors of ways to mitigate radon as opposed to simply affecting it to some degree. Good discussions.

There ain't NO free lunch. Not no how, not no where!

(post #115478, reply #10 of 73)

Clew,


You are correct in that it is not the proper way to provide combustion air to a furnace.  If the 80% furnace is in a tight room it won't meet code.  However, it was often done for combustion air and could still be done for other appliances, think large gas stoves,  remote waterheaters, fireplaces, gas logs, fart fans...  There are, however, much better ways of getting to the goal with current technology,  the OP wanted to know more about it. 


Some houses are negative for a variety of reasons.  It keeps the structure from behaving like a giant vacuum cleaner for the radon gas located in the dirt under/around the foundation.  Like I said, part of the process, especially with dirt floor basements, old open chimneys, unsealed crawl spaces, etc.


I agree with many of the other posters that sealed combustion and an HRV is probably the best long-term answer with the current energy forecast.  Then the home can be properly sealed and humidity, fresh air etc. can be properly controlled and energy use minimized.


Chris

(post #115478, reply #2 of 73)

This setup is common in this part of the country, and often is done without a damper -- just a relatively small port with 2-3 inch duct.

Note that the duct should be insulated to prevent sweating in cold weather.


Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115478, reply #3 of 73)

If you are replacing your furnace, why not replace it with a 90%+ efficiency model that draws its combustion air from outside?  I can't imagine why anyone would replace a furnace with anything else in this day and age.


I don't know where you are located, but sucking freezing cold air into your house ducting system is a very bad idea.  If you need fresh air in the house, you should go with a heat exchange system. 


If you just want combustion air, then go with a new furnace with a sealed combustion chamber using outside air.

(post #115478, reply #7 of 73)

"If you are replacing your furnace, why not replace it with a 90%+ efficiency model that draws its combustion air from outside?"

I agree that the sealed combustion units are by far the best, but combustion air is not the problem the OP is trying to solve.

"I don't know where you are located, but sucking freezing cold air into your house ducting system is a very bad idea. If you need fresh air in the house, you should go with a heat exchange system."

That all depends on your climate. What's right for Tulsa may not be right for Duluth.

 


Jon Blakemore

RappahannockINC.com

Fredericksburg, VA

 

Jon Blakemore

RappahannockINC.com

Fredericksburg, VA

(post #115478, reply #11 of 73)

The only logical use for a system like he's talking about is to supply makeup air for a furnace that uses air from inside the house for combustion.  Many localities require these to be installed.  That doesn't make it a good idea! 


In his case, he would be far better off installing a 90+ furnace that uses outside air for combustion.


If he wants fresh air, he can open the window or use an air exchanger if that suits the purpose better.


If you have ever seen the effect of sucking below zero air into your air ducts in the winter, you would not be a fan of such a system.


It makes no sense in the summer or the winter unless you need makeup air for the furnace and in that case you should provide it to the combustion intake area, not the ductwork.

(post #115478, reply #12 of 73)

If it's such a bad idea, why do I see the technique used in Minnesota?


Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115478, reply #13 of 73)

They use it in many states .  The sole purpose is to prevent negative pressure in houses that have been sealed up better than they used to be.  This was a shotgun approach at best.  They cause problems when it's cold in the winter or hot in the summer.


The primary culprit in creating negative pressure was the furnace or boiler sucking air out of the house.  With the new appliances, most of the cities we work in have dropped the requirement for these systems because they were so inefficient.  We have to install air exchangers in every new home we build now.  More costly, but certainly a better way to handle the problem.


In the OP's case, he would probably eliminate the need for such a crude system simply by installing a more energy efficient furnace instead of the one he is planning to install.


Most people that were required to install these systems have long since plugged them up so they don't work anymore because they caused them so much trouble when it got really cold outside. 


They did work, but certainly cost a lot of heat $$ to the homeowner.