Calculations on Vent-free gas appliances

[saichele]

This is mostly a matter of getting someone to check the calculations (esp. if you've done similar calculations yourself).

I'm contemplating installing a gas stove as a part-tim space heat option in a cold corner of the house. At the maximum, I anticipate maybe half a million BTU's per day. So half a million BTUs of NG makes .02 lb of CO and about 60 lb of CO2. Of course, the regs are all concentrations by volume, so I convert that over to about 13.5 m3 of CO2 and about 8L of CO (0.0079 m3).

I figure the house is 2400 sf, with 8ft ceilings makes it 19200, or 543 m3. so if there's no turnver of air, after a day of burning flat out, I'm at 0.000014 (14 ppm) CO, but 0.0248 (24,800 ppm) CO2. Regs are 35ppm CO and 800 ppm CO2.

Do these numbers seem reasonable?

Thanks
Steve

 

[Metal]

I wouldn't even consider a lung vented appliance.

 

[saichele]

Yea, yea. I sort of expected that response. What I'm actually trying to ascertain is the expected level of risk. Most people don't think anything of cooking a turkey in the oven for 6 hrs, and that vents to the room too. So they are safe at some speed, the question hinges mostly around my actual circumstance, not a knee jerk reaction.

Steve

 

[elkimmeg]

I don't know if this will help you but I tend to doubt my electricc stove produced many Co cooking the bird one day a year, and not set to a thermostat to kick on at any day
also my stove hood is vented to the exterior. I have to agree with metal better you breathing combustion exhaust than me and for those with allergies I wouner what combustion exhaust will interact with that?.. Many states allow Ventless appliances under 10,000 Btus But better check with the state, as they could have a list of approved ventless appliances. Make sure you install the manufacturer and model on that approved list.

Luckey me Because they are gas and do not require venting I don't have to inspect them. Its the fire dept and the gass inspector's job. Also better talk to theFd about monoxide detetectors
and placement. The NFPA and national gas codes require Monoxide detection coverage and not limited to just the room where the appliance is installed

 

[thechimneysweep]

Hi Steve,

Conversions tend to make my head spin, so I tackled this sideways, and did a little rounding to boot:

In order to consume a half-million btu's of gas per day, you'd need to burn a 30,000 btu vent-free for about 17 hours (17 x 30,000 = 510,000).

A 30,000 btu vent-free produces about 27 cubic feet of CO2 per hour, so in 17 hours, the vent-free would produce about 460 cubic feet of CO2 (27 x 17 = 459).

If you emptied your house of humans, furniture and other objects, it would contain 19,200 cubic feet of room air, so 460 cubic feet of CO2 would comprise 1/42nd of the total volume (19,200 / 460 = 41.74).

One million divided by 42 is about 24,000, so 460 parts per 19,200 parts is roughly the equivalent of 24,000 parts per million. It looks to me like your calculations are valid.

 

[hookspacken]

Call me ignorant, but I have always wondered, how is it that the ventless gas stoves work without CO2 risk? Is there come kind of catalyst inside the stove that reacts and reduces CO2 emissions? Jus wondering.

 

[karl]

No hoodspaken there isn't. Atleast no in the ones I have seen. I think they work on the principle of most people who used them have leaky old houses. This will make Elk have a fit, but I put one in my bathroom. Big time against code, but I love it. I get up in the morning turn it on and in tens mins the bathroom is toasty warm. I just made very sure my wife didn't use when she took a bath. I didn't want her to fall asleep and suffocate.

 

[stoveguy13]

If it is under 10,000 btus it can go into a bathroom. but you should check local code as some states have some variations on gas code

 

[saichele]

Hi Steve,

Conversions tend to make my head spin, so I tackled this sideways, and did a little rounding to boot:

In order to consume a half-million btu's of gas per day, you'd need to burn a 30,000 btu vent-free for about 17 hours (17 x 30,000 = 510,000).

A 30,000 btu vent-free produces about 27 cubic feet of CO2 per hour, so in 17 hours, the vent-free would produce about 460 cubic feet of CO2 (27 x 17 = 459).

If you emptied your house of humans, furniture and other objects, it would contain 19,200 cubic feet of room air, so 460 cubic feet of CO2 would comprise 1/42nd of the total volume (19,200 / 460 = 41.74).

One million divided by 42 is about 24,000, so 460 parts per 19,200 parts is roughly the equivalent of 24,000 parts per million. It looks to me like your calculations are valid.

That's the kind of thing I was looking for. Thanks. And, based on that, I'm reluctant to look at the vent-free option.

In point of fact, I suppose using a 30K BTU stove for more than an hour or so probably puts you over the 800ppm limit.

Steve

 

[stoveguy2esw]

Call me ignorant, but I have always wondered, how is it that the ventless gas stoves work without CO2 risk? Is there come kind of catalyst inside the stove that reacts and reduces CO2 emissions? Jus wondering.

vent free gas units have whats called an "ODS" or oxygen depletion sensor system. what this does is basically shuts off the gas when oxygen levels deplete to just above 19 percent in the room that the heater is located in. this component is internal to the stove and works through the pilot system. essentially , when normal amounts of oxygen are present , the pilot flame is strong as it is supposed to be , as the oxygen level drops, the flame becomes weaker, this causes the pilot flame to lift away from the thermocoupler (which energizes a spring loaded magnet in the valve body). as the flame lifts off the thermocoupler, it will no longer generate the electrical current that holds the magnetic valve open, at this point, the spring loaded valve shuts cutting off the gas to both the main burner as well as the pilot itself. the unit cannot be restarted until the oxygen level is regenerated to acceptable levels as the pilot flame must heat the thermocoupler to start the current and theis wont happen as the flame will not be strong enough.
as for the low output of co and co2, the way the gas is jetted and burned causes a very low release of co and co2 when compared with the actual burning of a vented gas stove , which are sealed units and vented for that reason. now getting back to the depletion of oxygen in the air in the room, the room that the unit is to be installed in must meet the size requirement of the "confined space rule" in order to function (essentially this means the room must be large enough to have enough ambient air in it to satisfy the stoves requirement as well as maintain above 19.1 percent. to figure confined space use the following equasion L x Wx H x 1000 /50 (or length times width times height , times 1000, then divide that total by 50.)now , and this is important; the total you come up with for your math must be HIGHER than the max BTU output of the unit. if it does not , it cannot be used in that room. other rules include not having the unit in a sleeping room , or a bathroom, or a hallway. and DEFINATELY , HAVE CO AND SMOKE DETECTORS IN THE DWELLING WHEN USING ANY FLAME PRODUCING APPLIANCE (i dont care what it burns , if it makes a fire, get these detectors!) for more information about vent free gas , google the vent free alliance , or GAMA.

sorry for being longwinded, hope this helps ya!

mike ESW

 

[elkimmeg]

No hoodspaken there isn't. Atleast no in the ones I have seen. I think they work on the principle of most people who used them have leaky old houses. This will make Elk have a fit, but I put one in my bathroom. Big time against code, but I love it. I get up in the morning turn it on and in tens mins the bathroom is toasty warm. I just made very sure my wife didn't use when she took a bath. I didn't want her to fall asleep and suffocate.

No sweat off my back, they are not in the realm of my inspections Its up to the gas inspector and th FD to ensure their safety. Better you than me breathing combustion air

 

[hearthtools]

Dont forget all the Moister it will put into the air.
will make your walls yellow
Lots of horror stories.

 

[saichele]

Call me ignorant, but I have always wondered, how is it that the ventless gas stoves work without CO2 risk? Is there come kind of catalyst inside the stove that reacts and reduces CO2 emissions? Jus wondering.

now getting back to the depletion of oxygen in the air in the room, the room that the unit is to be installed in must meet the size requirement of the "confined space rule" in order to function (essentially this means the room must be large enough to have enough ambient air in it to satisfy the stoves requirement as well as maintain above 19.1 percent. to figure confined space use the following equasion L x Wx H x 1000 /50 (or length times width times height , times 1000, then divide that total by 50.)now , and this is important; the total you come up with for your math must be HIGHER than the max BTU output of the unit. if it does not , it cannot be used in that room. other rules include not having the unit in a sleeping room , or a bathroom, or a hallway. and DEFINATELY , HAVE CO AND SMOKE DETECTORS IN THE DWELLING WHEN USING ANY FLAME PRODUCING APPLIANCE (i dont care what it burns , if it makes a fire, get these detectors!) for more information about vent free gas , google the vent free alliance , or GAMA.

sorry for being longwinded, hope this helps ya!

mike ESW

Now that's an interesting calculation, because it yields an entirely different outcome than the previous one. The room I was considering is 12' x 14' by 9' (just assumed 8' through the whole house inthe previous, wouldn't have changed the result) so using your method I come up at volume = 1512 cu ft, times 20 (whats with multiply by 1000, divide by 50 anyway) = 30240, so under your srtucture a 30K BTU vent free would be OK - despite being seemingly way over the appropriate emissions levels based on the previous calculation.

So now - what's the source or technical reference for your calculation?

Steve

 

[webbie]

There is another reason that these calculations may not mean much - that being that from the first minute of use, a vent-free appliance will become less and less "tuned" as the days, weeks and years go by. In other words, expect an older vent free to produce a lot more of certain pollutants than one right off the line!

I know - that isn't technical, but it is true!

Here are some other experiences - when a vent-free is tested for pollutant output, it is not put into home environment where vast quantities of OTHER gases are present - outgassing of carpet, wood, paint, etc. - Expect these to add more to the cocktail mix.

And now for the story(s) that you certainly didn;t ask for - like the industry meeting I attended which included many sellers (reps, distributors, etc.) of vent free - and one person dared to ask "who here would have a vent-free in their home?" - No hands went up!

Or, the customers that we sold them to who were very happy and continually stopped by the store telling us how great the fireplace was - UNTIL one day, something went a little out of wack, and a layer of soot was deposited on every surface in the house - talk about a clean-up!

Based on all those experiences and more, I cannot suggest a vent-free appliance for anything other than perhaps 10 hours or so a week of fully attended operation.....and I would not have one myself except perhaps in a breezeway.

 

[stoveguy2esw]

i'd have to look up the root source for that calculation , its actually in our vent free units manuals. as for the levels of pollutants , check out the vent free alliance website http://www.ventfreealliance.org/indoor.htm

 

[thechimneysweep]

If you visit the vent free alliance website, you're going to get a pretty one-sided picture of vent-frees. This is not surprising, as the alliance is comprised of vent-free manufacturers. For a look at another side of the vent-free debate, check out the letters page on our website at http://www.chimneysweeponline.com/hovflett.htm. For more info, click the links at the bottom of the page.