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Mechanical Room In Basement

Zano's picture

Started a few basements remodeling and now am asked to do two new basements in new houses that are just 2 months old.  Why in the blazes do they locate the mechanical devices almost in the middle of the basement?


How about putting the HVAC and water heater in the corner of the basement?


One homeowner told me that they wanted to put the mechanicals six feet right in front of the walkout door while his basement is 83' x 62' and he convinced the that's a bad place.  I little common sense from the builder, does he not realize that some or most homeowners would want a finished basement and then why locate the mechanicals almost  right in the the basement..fine home building..forget about it.


Also why does the building department want drywall at the 1st floor joist next to the exterior wall before you put the framing up..what's the purpose as the basement ceiling and the exterior walls will be rocked anyways?

(post #69526, reply #1 of 19)

>>Why in the blazes do they locate the mechanical devices almost in the middle of the basement?

>>How about putting the HVAC and water heater in the corner of the basement?

The furnace will operate best when centrally located; fewer problems with uneven heat distribution.

And the water heater usually goes by the furnace for gas supply and venting reasons.

Since you didn't know that, I'll just mention in passing that the furnace and water heater need a lot of combustion air - do not enclose them without making adequate provision for combustion air. (And don't forget future service needs.)

General rule of thumb for combustion air: for taking combustion air in from the house itself: 1 sq in _free_ vent space for every 1,000 btu combustion, minimum of 100 sq inches. (E.g., 100,000 btu furnace and 32,000 btu water heater: 132 sq inches free vent space.)

1/2 at the top of the utility area, 1/2 at the bottom.

Put a grill over the hole, and you lose 30% to 50% of the Free vent space. (in others words, a 10" x 10" opening becomes a 7x10 to 5x10 after you put the grill on.

Put a grill on both sides and, I _think_ you've reduced it even further, but I've never met anyone who knows actually the answer on that one.)

(BTW, in my opinion, if you modify the room so as to affect combustion air supply, you become responsible for determining proper venting: vent tables are guidelines only.)

======================================== "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 #69526, reply #3 of 19)

Bob,


I appreciate youtr detailed analysis and as I'm not well versed in these matters, I still cannot understand if the in house air units were placed say in a corner and four feet from the basement foundation on each side that the amount of air would not be adequate.


If the units obtain air from the outside, then does locating the units almost in the middle of the basement a necessity?


I just cannot realize that in today's age those units cannot be located near a corner resulting in a wide open basement living basement area.


But I'm getting to see the light!

(post #69526, reply #5 of 19)

Two different air issues ....

The central location is to facilitate optimal districution of the air warmed by the furnace.

I'm sure a system can be designed allowing tucking the furnace off in a corner, but I expect (I'm far from an expert in this area) there are significantly increased cyhances of getting it screwed up with expensive callbacks and corrections.

The combustion air issue is completely different: so long as the furnace and other combustion appliances get enough air, they don't care where they are located.

======================================== "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 #69526, reply #7 of 19)

The central location is to facilitate optimal districution of the air warmed by the furnace.


Wouldn't this prosume someone actually cares about a home's thermal performance in terms of heating and cooling and maintaining such heated or cooled living space? I find it almost comical that any county in my state would suggest 'they care' when any delivered 'conditioned' air is immediately swept from the home due to poor construction that the counties/state doesn't code for.


The combustion air issue is completely different: so long as the furnace and other combustion appliances get enough air, they don't care where they are located.


Curious about this apsect. If the combustion at the furnace requires in-home air for that combustion process (as opposed to sourcing it from outdoors), then should there (rationally, speaking) be a CO2 sensor as well to insure combusted products are not fed back into that otherwise seemingly closed system?


Also, in a setup (design) in which the air needed for combustion comes from air inside the home and its drawn up the flue during the combustion process, wouldn't this bring air from outside into the home in order to re-establish an equalibrium-state of air pressure between inside and outside? Sounds almost like one should run a vent from outside directly to the mechanical room for the point of combustion (furnace), and then seal the mechanical room.

(post #69526, reply #9 of 19)

>> >>The central location is to facilitate optimal districution of the air warmed by the furnace.

>>Wouldn't this prosume someone actually cares about a home's thermal performance in terms of heating and cooling and maintaining such heated or cooled living space? I find it almost comical that any county in my state would suggest 'they care' when any delivered 'conditioned' air is immediately swept from the home due to poor construction that the counties/state doesn't code for.

I don't think this is a code issue - simply a matter of common practice and the common sense idea that a builder &/or HVAC contractor wants to minimize the likelihood of call backs if it doesn't cost too much.

It has been said that uneven heat distribution is the biggest complaint re HVAC systems

======================================== "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 #69526, reply #10 of 19)

Several points you touched on, the first being someone caring about the performance of the heating/cooling system. Obviously someone was thoughtful enough to centrally locate the mechanicals to best perform their function. Hopefully, those like Zano will ask and learn the reasons for such placement and not mindlessly locate these units somewhere out of the way. They can be located anywhere, within reason, however, like just about every other aspect of building, compromises will be required.


CO sensors are requiired whenever fuel burning appliances are located within the living space. Backdrafting is frequently an issue when ALL aspects of the installation are not treated properly. Most homes are not sealed so well that combustion air is not readily available, unless the equipment is closed within a comfined space. Mechanical codes exist to prescibe how this is to be addressed. One who has no clue as to why someone would locate mechanical equipment centrally, has no business touching said equipment or modifiying the space in which there are located.


"Sounds almost like one should run a vent from outside directly to the mechanical room for the point of combustion (furnace), and then seal the mechanical room." As alluded to above, when conditions are such, code requires exactly what you mention. As houses are constructed tighter and/or weatherization projects seal up leaky homes, combustion air is usually ignored until either the equipment fails to operate properly or the occupants are killed. Not the area in which amatuers and uninformed folks should venture.


Edited 12/19/2005 9:02 am by Tim

(post #69526, reply #12 of 19)

I guess I am only going with observation-based experiences, and what I have in my home. I'm in the south, in a track home, and the learning processing only minimally enhanced by getting builder (superattendent) feedback.


First, no CO sensors in my home or anyone elses per builder or code enforcement. I guess its not a requirement for these gas heated homes with centrally-located furnaces. Second, its almost always the case in my little subdivision that the county inspectors issue the cert. of occupancy before the builder fniishes a basement for new homeowner, but certainly nothing is said by inspected post-sale basement completions.


So, I would imagine that the centrally-located is either a code requirement by the county/state and or the HVAC person found this to be the easiest approach to gettng the most performance out of the least system installed. Now arguing the reasons why its centrally-located, but rather the logic is only as good if other factors follow the same philosophy, and in my case they don't.


I can point out a dozen homes in my subdivision all less than 5 years old with builder-finished basements where the doors to the mechanical room are tight for sound insulation, and no other visible means to provide air. I suspect this is combination of no-codes, lazy code enforcement, or something else. All I know if that the finished basements on new construction do not seem to meet the ethical and or logical approaches being suggested, regardless if its post-sale completion by homeowner/contractor or by the builder.


So, while it may not be wise for a home owner to effect a change on the mechical room itself, like installing drywall and a door, there certainly doesn't seem to be an ethical or rational basis by the county/state to insure of this. Should this be taken as a homeowner also accepting a hell-be-damned attitude? Of course not. But I am reporting observations for modern southern construction in my neck of the woods.

(post #69526, reply #15 of 19)

Mechanical and electrical installations in residences and commercial/institutional/educational facilities around the country do not comply with codes, common sense or good practice and yet people continue to survive. However, most of the code provisions for providing adequate combution air were instituted in response to some tragedy. CO sensors are not required by many codes. Physical location of appliances are not specified by codes, as far as I am aware, though general provisions for access, clearance, and combution air typically are to some degree. That my simply be "per manufacturers recommendation" in many instances. Central location is a matter of practicality, at least to me.


"..certainly doesn't seem to be an ethical or rational basis by the county/state to insure of this". I would bet that there is a comprehensive building code on the books in the county where you have observed these issues. The rationality of some building codes could be vigorously debated, but some direction, leaglly binding, is in place. Bewteen "good ole boys"', incompetence, laziness, limited resources, ignorance, nepotism, and probably a few other maladies, your county is dropping the ball. This is not a southern problem, it is a local problem.

(post #69526, reply #11 of 19)

I split my responses based on the two subjects:

>> >>The combustion air issue is completely different: so long as the furnace and other combustion appliances get enough air, they don't care where they are located.

>>Curious about this apsect. If the combustion at the furnace requires in-home air for that combustion process (as opposed to sourcing it from outdoors), then should there (rationally, speaking) be a CO2 sensor as well to insure combusted products are not fed back into that otherwise seemingly closed system?

Yep, safety experts recommend CO (carbon monoxide) detectors (not CO2 - a common typo) on each living level. My own view is to put the first one in the bedroom of the most "medically vulnerable" person living in the house (use a battery powered type, mount it at about eye level or slightly above); put the second in the area of the combustion appliance, etc.

>>Also, in a setup (design) in which the air needed for combustion comes from air inside the home and its drawn up the flue during the combustion process, wouldn't this bring air from outside into the home in order to re-establish an equalibrium-state of air pressure between inside and outside? Sounds almost like one should run a vent from outside directly to the mechanical room for the point of combustion (furnace), and then seal the mechanical room.

This is a really complex area - you've got it right, but there is more to the story

When using outside combustion air to feed the utility room (as opposed to direct vent appliances with a completely sealed combustion system, including a sealed air feed from outside,) there should be two pipes, one feeding high into the utility room, one feeding low. (Note, there are techniques for reducing cold air spillage: an upside down goose neck at the bottom or discharge into a box with no top)

For natural draft appliances ("atmospheric" with a drafthood or barometric damper, or mid-efficiency '80+' furnaces) the desired draft is only 0.01 - 0.02 wcin (water column inch.) That is roughly equal to gently blowing out a match at about 6" or so - not much force at all.

I've been testing the draft on gas appliances for about 5 years now - and have concluded that although there are some "general rules" the only way to tell how a unit is drafting is with a draft gauge properly used.

Even the GAMA vent tables specify that individual conditions can affect performance and that the "designer" is responsible for actual performance in the field.

I checked a house a couple of months ago; the flues for the water heater and furnace were 'properly' designed per the GAMA vent tables.

But, in fact, they didn't vent properly.

The flue exited from the one story garage roof about 14' from the second story sidewall. (10' required from any such sidewall.) It had sufficient clearance above the roof for the pitch of the roof.

The rise and run and vent pipe sizes were dead on.

I have tested several other houses in that neighborhood, same basic configuration, no problems.

But that house didn't work right. I think that particular house siting, orientation to the prevailing winds (very slight breeze on the day I tested) happened to create "higher" pressure at the top of the flue reducing the draw.

======================================== "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 #69526, reply #13 of 19)

Are the CO sensors at eye level while laying down or standing? If it's at standing eye level, it could still be a problem since OC is heavier than air, at least when there are no major temperature deviations. Basements bedrooms are really an issue with this as well as Radon. Warmer CO, being less dense, can rise but by being less dense, isn't as much of a risk because of it's decreased concentration. However, after losing a friend last year due to CO poisoning, any CO is a risk. Apparently, it may not have been accidental, but he was a firefighter/EMT and he's just as gone as if it had been.

"I cut this piece four times and it's still too short."

"I cut this piece four times and it's still too short."

(post #69526, reply #14 of 19)

>>Are the CO sensors at eye level while laying down or standing? If it's at standing eye level, it could still be a problem since OC is heavier than air, at least when there are no major temperature deviations.

CO (carbon monoxide) is basically the same weight as most of the other gases making up air; perhaps you're thinking of CO2 (carbon dioxide) which is distinctly heavier than the rest.

And, real world, when I've been called out to test houses with CO problems, the CO levels are highest the higher one tests in a room. CO is in hot combustion air when it gets into a house, and rises.

My fellow CO safety analysts report the same results.

And don't forget, high levels of CO can kill, but long term exposure to lower levels can cause serious long term health problems.

"Just 'cause you aren't dead doesn't mean you don't have a CO problem."

======================================== "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 #69526, reply #17 of 19)

QUOTE:


This is a really complex area - you've got it right, but there is more to the story


When using outside combustion air to feed the utility room (as opposed to direct vent appliances with a completely sealed combustion system, including a sealed air feed from outside,) there should be two pipes, one feeding high into the utility room, one feeding low. (Note, there are techniques for reducing cold air spillage: an upside down goose neck at the bottom or discharge into a box with no top)


A lot more complex than most housing and technical types believe.


For example, the Wood Energy Technical Training (WETT) manual, basis of the course that certifies the wood heating industry in Canada, removed the outdoor combustion air recommendation in 1998 unless directly stated and required by the manufacturer. (I was on the national WETT board at the time) The title of the sidebox explaining this was: Outdoor Combustion Air......An Idea Who's Time has Come and Gone.


CMHC, our national housing agency, did some testing with backdrafting in traditional open wood fireplaces. The results: Even with a 10" diameter supply in wall near the fireplace, when a certain combination of appliances came on (dryer and good size range hood) the 10" opening could not passivley relieve enough negative pressure and the fireplace backdrafted. The 1990 building code here required combustion air for fireplaces; the 1995 code made it optional since it wasn't dependable.


One thing that most do not realize, is that any passive vent such as mentoned above (goose neck) is subject negative wind pressures when it's on the lee side of the house- air will be sucked out of the house or furnace room!!! One day when I was a phone-based energy advisor for the provincial gov't, I had a call in the summer about some previous winter's backdrafting problems. Talked to the homeowner for a while and realized that the right conditions were in place for the supply to suck out of the house as there was a small wind that day. Asked the homeowner if he smoked and yes, he did. This was an oil furnace setup (very safe in relation to gas) so I asked him to light a cigarette as a smoke source and go to furnace area. He put lit cigarette down by combustion air supply- it sucked smoke out of room. This was in light summer wind and not some of the winter nor'easters we get here.


Starting 1992 at every local WETT training course, I used to train 2.5 hours on "house pressures" and "combustion gas spillage" in a 3 day introductory core wood heating course. National now has developed 2 one day courses on the same topics titled Smoke Spillage and Backdrafting and Managing House Pressures!!!!


In every WETT core course, a homeowner video of a shocking occurence is shown:


A cool fall day with a factory built zero clearance airtight fireplace burning a low fire. The flames of the fire occasionally seem to disappear and go down through the firewood.  Home owner takes video camera outside to film the direct connected combustion air supply and eventually in a high wind gust, smoke comes out of the supply hood.


Explanation: Supply hood was in lee of high wind gusts strong enough to suck air from the supply vent. Combustion air was beiong sucked down the chimney, hence the flames disappearing down through the firewood and smoke going out the combustion air supply venting- totally the opposite of design. The supply venting is not insulated and certified as a chimney so this becomes a big fire hazard. This installation was on the main floor of a house with the combustion air supply run between the main floor joists. It has been postulated that if this heating applaince was in a basement installation with a vertical supply vent down from the rim joist, in the wrong situation of steady high winds, the supply might become the chimney due to ts vertical orientation!!!


Edited 12/19/2005 9:57 pm ET by experienced


Edited 12/20/2005 7:15 am ET by experienced

(post #69526, reply #18 of 19)

Wow!

Thanks.

======================================== "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 #69526, reply #19 of 19)

How does this take into account other methods of building rsidential homes? For instance, let's say I have a two-story on basement,  one-sided OSB/plywood SIP with timber-frame shell. How does one apply the fire-trap protection philosophies? Or, how about the same two-story on basement using two-sided OSB/plywood SIP with frameless shell?


Of course I am leading up to 'something' by asking this and its when one now takes the gray area between conventional stick construction and cellulose/fiberglass insulation and move to stick with spray-on expanding foam insulation. The non-blocking stud cavity would be completely filled and 'tight' due to the nature of expanding foam insulation and created something much like a SIP situation.

(post #69526, reply #8 of 19)

Air likes to become turbulent over long duct runs or going through transitions and this slows it down, reducing the flow to the farthest areas. Centralizing the furnace cuts down on this issue and it's not going to change any time soon. Sure, it would be nice to get all of this stuff out of the middle of the house, but you can bet that it has been tried with bad results. The combustion air coming from the outside isn't the problem, it's getting the heated/cooled air to the far reaches of the building.

"I cut this piece four times and it's still too short."

"I cut this piece four times and it's still too short."

(post #69526, reply #2 of 19)

The strip of drywall the inspector is talking about is fireblocking. AKA  fire-stopping, draft-stopping, .  Ive used a wide piece of metal framing  track with one flange hammered down flat so it looks like an  L   .  

(post #69526, reply #4 of 19)

I just don't understand the logic of doing the fireblocking.  I've done plenty of commercial jobs and understand the necessity for fireblocking and draftstopping, but if the basement did not require this fireblocking at it's inception why does it require it now especially when that upper wall corner around it's entire exterior perimeter will be sealed with drywall.  Always wanting to know why I must do something!  I was informed by an ex-employee of mine who also does basement renovations that there is a way of circumventing this requirement, he explained it to me over the phone, it has to do with how the permit application is presented.  I'll find out the details and will revert.

(post #69526, reply #6 of 19)

If a fire starts in the framed wall of the basment, it would have unabated access to the floor above.Thus the firestoping befor the new framed wall.

(post #69526, reply #16 of 19)

If a fire starts in the framed wall of the basment, it would have unabated access to the floor above.Thus the firestoping befor the new framed wall.


Now that makes sense!  I accept it now!