Expressway to Disaster

[elkimmeg]

Let me explain: I quit work today because it was too hot. Goose and others asked me to comment on this issue.
Goose, Begreen or any other members if you want to clean up this post and submit it to our wiki system, be my guests This situation will reoccur many more times. It would be easier to supply a link.
Again the post exceeds the character limit so it is split up.

To Gunner no manufactures are mentioned. To BB I did add a little humor can’t always let you have the monopoly. MR Griz How is that permit application going? If you need help just e-mail me


One of the main issues her is removing immediate combustion air creating a vacuum or negative pressure

Stove manufactures have hit a wall they can only do so much to extend burn times and meet EPA particulate

requirements. Part of the problem is to make the stoves more efficient, they reduce draft. No science needed,
reduce the heat leaving up the chimney,, more heat left in the stove to transfer to the living space

When the burning season begins, so will the post wondering why their stoves run poorly. 90% maybe more suffer
from weak draft or negative pressure locations. One solution is to crack an adjacent window this relieves the negative pressure,
plus add needed makeup combustion air

Think for a minute and now add a mechanical means of removing air in the vicinity of that stove. What happens when a weak draft suffers
from reduced pressure and a vacuum forms? That mechanical device stands a good chance of back drafting the stove exhaust into the living space
Even if this does not happen, the draft efficiency is reduced and draft is the engine that makes the stove work. That is why code requires no returns within 10' of the stove

Lets discuss HVAC systems: First of all systems with ceiling returns are the least efficient. A design IF code allowed, I would fail every time .
What is the sense of returning the hottest air. How does one draw down lighter hot air in to the lower comfort zone of the living space.
Let me clue you it can't happen with ceiling returns In order for that system to function efficiently one must remove the heavier cooler bottom layer of air
Once that heavier air is removed it creates space for lighter warmer air to occupy. I can't tell you the number of post where people add supplemental heater,
because they never seem to get warm. So many times the furnace is designed to the correct capacity but the ducts or transmission system is poorly designed and installed

There are a few ways one should consider reducing heating bills Supplemental heat is one
The second way is to improve your existing heating system. All exposed ductwork should be insulated to above R.5.0 and every joint duct mastic sealed.
Up to 35% heat loss in due to transmission. Hot water systems insulate those pipes

The third consideration is adding insulation and draft stopping. You paid to generate the heat might as well enjoy it a bit longer

LET me critique the person who cuts in an additional return vent above his stove. Today’s Hvac systems are balanced. Usually there are dampers installed in every lateral take off

Using a flow-measuring device, the volume is adjusted to even out the flow. This method eliminates the cold room at the end of the run. Each room requires the correct volume to heat it. For instance, a 6" duct is capable of up to 150 cfms. Without boring you with a lot of complicated math, should satisfy a normal 12 /12 room. Add wall to wall glass, naturally a greater heat loss requiring more volume.

What happens to that balanced system when additional outlets are added? Remember supply = returns That ceiling opening just eliminated the balance and reduced the entire system efficiency That does not mean it can't be balanced again, but chances are Joe homeowner does hot have the equipment of knowledge to do it and never even considered the need.

 

[elkimmeg]

We will touch upon life safety issues later: So Joe homeowner has the poorest designed ceiling return system available and he just reduced its efficiency And he brags how he is able to use it to distribute warm air? A system that should be designed to move cold air? As bad as the main trunk supplies leak, let me tell you floor and ceiling joist cavities, used as return plenums is worst. Almost impossible to seal. So leaky so inefficient, but cheap to install.. You know in commercial construction it is illegal to use joist bays for returns? The reason is safety. IF I had my way no combustibles would comprise any part of the HVAC systems. But it is allowed usage in residential construction to reduce cost. Another issue is the temperature Return bays are allowed because the temperature range is less than 120 degrees. Well wood does not burn at 120 so what is the problem. Today’s home are constructed with engineered joist
composites that are glued together. When that glue starts melting, there goes a piece of structural integrity.

Speaking of engineered joist: What do they bring to the table? Longer unsupported spans and the ability of more open floor space strength that can't be matched,
using normal dimensional lumber Another advantage is they do not have to be spaced 16" on center many are 20" or 24" a cost saving factor. All this sound too good to be true a win win situation which manufactures present. But what are they not telling you is there a trade off? You bet, big time safety issues. It seams when exposed to heat the glues melt and structural integrity vanishes quickly, 100 time faster than common dimensional lumber. Fire fighter are instructed not to enter homes with these joist structures once the fire gets beyond a certain intensity. No floor is safe for any fire fighter and it happens 100 time faster than conventional lumber. That time window to rescue occupants is very limited.
This is one of the fact one just goes Arhh nobody ever pointed that out.. I never knew. Certainly the manufactures are not publishing this Data. As a building inspector, these are approved engineered joist acceptable in code. Would I use them in my own home? Not in my lifetime.

So now you are using that mechanical fan in your HVAC system to extract heated air above a wood stove What happens in times of weak draft? That fan does not recognize Carbon monoxides entering your system. Since it is invisible and odor less neither do the occupants.. AT what time are we most vulnerable to exposure? You guessed it when we are sleeping.
Why do you think smoke detectors are required in every bedroom? That Joe homeowner, who in his engineering marvel, just created the express way to disaster. There are no safe guards, that mechanical fan will keep pumping in nasties In the event of a fire
That express way reduced your safety exit time. In fact it will draw the smoke and flames right into the system and keep pumping away and with each passing seconds as the air smoke is heated and lightened it can push more and more beyond it original intended volume.
I have gone to seminars where videos are presented detailing house fires. You do not have the time you think you have. That return fan is almost creating a blowtorch effect to that FIRE.

I HOPE THIS SCARES THE CRAP OUT OF YOU IT IS REAL AND NOT EMBELISHED. If you showed this post to your wife and she realizes the increased risk you will be boarding up the return tomorrow

So why would building inspectors sit in on firemen training films?

Containment: Containment buys valuable seconds for safe exit.

The next time an inspector is bashed here think of what some of us do. My rough frame inspections go well beyond structural integrity
Equally as important is fire draft sealing and fire blocking/. I take life safety issues serious. I go so far as checking the sealant around wire protrusions. Common caulking will not cut it.. IT has to be certified fire stop draft concealment ASTME 136 1200 degrees minimum requirement. The electrician knocks out a fire block the inspection fails. The better I do my job the safer the occupant becomes. This has a snowball effect towards the builders. They know how demanding I am.. They learn very quickly the BS stops and it is better to get it right the first time. There is no compromise
And also it is my job to educate them. Its one thing to fail an inspection, but equally important to explain why.. Failure is easier to except when explained.

Now lets get back to Joe homeowner Naturally he has never factored in the ramifications of his engineering marvel. He did not know ceilings and floors create natural containment barriers..

Why it does not work: pushing lighter warm air into heavier cooler air does not work. The heavier air will resist movement, being forced might penetrate near the immediate duct entrance but it will still loose out. The only way it can work is extracting the cooler air.

This is where Joe homeowner fell far short. He was thinking only in terms of moving warm air without understanding the physics or dynamics in doing so. What he should have done is move the cooler air towards THE HEAT SOURSE Thereby drawing the warmer air in to replace Remember I mentioned supply = returns

Think of it terms of the old style oil cans, you know the ones you used a church key to open. How well did the oil flow out one hole?

Add that second vent hole and the oil flowed consistently. Supply = returns

 

[elkimmeg]

Every now and then Joe homeowner engineering marvel works to some degree. It defies laws of physics or his system is designed so poorly it works.

I say this to that, even a blind squirrel finds an acorn occasionally

There are some risks I will take, but one of them is not reducing my familly’s safety, the dangers far out way any benefits.

To those willing to take the risk, Dirty Harry said it best do you feel lucky punk

At one time I listed all the code violations concerning these situations, I will let Begreen cut and past them as he did before

 

[webbie]

Am I missing something?
Does this post relate to another one? If so, which one? It seems to be lonely.

 

[elkimmeg]

Web I thought Goose would see a this and fill in the blanks. the thread he refered to is this one

https://www.hearth.com/talk/threads/8171/

 

[titan]

Some notable info there with regard to the engineered wood Elk,beyond it just being a bastard to drill and cut.thanx.

 

[babalu87]

Welcome back Elk and yes it is silly hot around here lately.

Now I am wondering about that one engineered joist in our house......... its in the living room where the stove is

Good thing we can all get out the front door if the need ever arose avoiding that room completely. Why arent the manufacturers made to use different glues or a coating to make the joists more stable in the event of a fire?

 

[webbie]

Some notable info there with regard to the engineered wood Elk,beyond it just being a bastard to drill and cut.thanx.

I would hope I was long out of the house before them thar particle board joists I have start to melt and burn.

Just about all houses around here seem to be made with these - Joe (or Craig, for that matter) naturally assumes that something which has passed all the tests is safe as far as statistics. Of course, safety is a matter of degree. When I built my shop, I was going to put some nice local pine boards on the interior walls instead of cheapo drywall. Then I dug up the fire ratings on the internet......and drywalled the shop!

The more of this stuff you hear about, the better deal those backup smoke and CO detectors become. As the pilots know, backup systems are the key to saving lives when the inevitable happens. Even though I have wired detectors everywhere, a couple extra won't hurt....and the CO one!

 

[webbie]

I say this to that, even a blind squirrel finds an acorn occasionally

My goodness, now we are gonna have to start a "famous quotes" wiki entry.
:coolsmirk:

 

[stoveguy2esw]

so, essentially moving the cold air back to the stove where it will be heated and happily moving on in the convection current of the house is a better choice? i think so.

assuming that it is cold air is more dense (it is), hence the reason it sinks, i have callers who say"i have a fan blowing into the other room but it still wont warm up" my reply, which gets a range of reactions from "huh?" to indignance, is to simply take the fan and turn it around and aim it into the room with the stove.

try an experiment next time you are warming a cool house with your stove; stand in the doorway to an adjacent room with a candle. holding the candle at your waist the flame will generally stand fairly straight up. now raise the flame to a safe but high in the doorway location and observe, the flame will lean towards the cooler room slightly. now here is the kicker , lower the flame to the floor , the flame leans back into the warmer room. this is a natural convection current.
by placing a fan on the floor to blow heat into a cold room , you are defeating that current and actually pushing what heat is trying to get in the room back out. reverse the fan, pull the cold air out into the warmer room and the vacuum effect of the cold air leaving will pull heat into the room over the top of the exiting cold air.

personally, i feel this is even more effective than using a high mounted doorway fan blowing in because the cooler air is more dense and will evacuate the room faster than the high fan can push the warm (less dense) air in.

no ductwork required and if the pressure in the room with the stove is affected, it will be positive pressure , which will not degrade draft, might even help it although not much

just my 2 cents

 

[littlesmokey]

This one's a head rubber for Elk and Mike. I have a cold room in my shop, I have tried a lot of ways to use the stove to warm it, but have been unsuccessful using the "old common sense". After reading these posts more than a few times, I have a new idea. Strange, for me, but I have a common wall at the back of the shop that I could put a 6 inch spiral pipe, at the floor from the farthest corner to the back of the stove. I have a few draft inducer blowers around that I can hook into the pipe and "push" the cold air from the corner to the stove and have it vent through a standard floor vent directly on the stove. At the same time, I can run a through the wall connector at a 6 inch to four foot height. That's a vent about a foot wide and covered with a low density filter. That would draw the warmer air back to the corner to replace the power vented air, right? Hope I get a cold snap right after I get the brain trusts approval for the install and can really test the theory.