Fresh Air INTAKE FOR COMBUSTION

[jimdeq]

My insurance company told me I needed a fresh air intake for my Tarm Solo 60. The boiler is in my attached garage and I built a 6'x11' boiler room around it with 5/8" firecode plasterboard and a steel fire door to the room. I was thinking about using 4" PVC from the attic down into the boiler room. Could I then use a U trap and then go back upwards. I have heard many different options ,but i dont know what is the best. My garage is not airtight anyway so I dont understand how much air I need? Can I just stub the pipe in the attic or do I need to pipe it out the soffit? Is 4 inch too big or small? Should I put a gate valve in the pipe?

 

[Hunderliggur]

Interested to hear the replies. However, a 4" gate valve is expensive. A 4" PVC cap (threaded or slip) is cheap. Does the same thing unless you are piping directly into the boiler.

 

[Como]

The Garn instructions mention this and it has an outside supply.

The plans show basically an air inlet at a low level coming up to provide an outlet at a higher level, presumably to mitigate air flow outwards.

Looks like regular rectangular ducting.

 

[Fred61]

Would the pipe be attached to some part of the boiler combustion air or would you be dead ending it somewhere in the room or under the boiler? My Wood Gun was piped directly from the outside to the combustion air intake box. Periodically, when the combustion fan short cycled I would get an explosion which would blow the hood I had over the intake about 20 feet out into the backyard. I know there was some fire shooting out too so if it were dead ended in the attic there is a chance hot coals could be spit into the attic. My EKO "sneezes" at times when the wood is burning faster than the oxygen can be provided to the fire but it happens so fast I can't decide if any hot coals are being spewed through the air intake and secondary air channels. I guess I wouldn't attach an air make-up pipe to a boiler if it were going to be dead-ended in the attic. Other than that I don't see any reason why you couldn't get sufficient make-up air from the attic.

 

[jebatty]

I think it is a little more complicated than meets first glance. 4" pvc (12" square) does not provide nearly enough makeup air for a Solo 60. The rule of thumb is 1" square free space for each 1000 btu rating, or just about 200" square for the Solo 60. Doing this through a fire rated damper is one way. This is free air intake into the boiler room, not a direct air supply to the boiler. The Solo 60 is not designed for direct outside air intake, and I would not even try that without consulting with Tarm.

 

[Piker]

Direct air intake is a no no on the gasifiers. You will have condensation issues, combustion efficiency issues, and refactory failure issues.

Passive air intake for combustion is tricky. If the air vent is on the opposite side of the house that the wind blows, it can actually create additional negative pressure inside the home since there would be low pressure on that side of the house. This can be a nuissance, if not downright dangerous. If the airvent is on the high pressure side of the house, of course you get way more air than is required.

The 1 square inch per 1000 btu rating is a rediculous standard in my opinion. That's alot of opening for a solo plus 60... like having a decent sized window open. here is a case, where code doesn't consider the other factors involved, like how much air the structure can supply through existing cracks and crevices. one size does not fit all, but not sure you have a choice in the matter.

Not having enough combustion air can definitely be a problem... if there is more than one flu in a chimney, smoke and products of combustion can go up one and be drawn right back down into the living space by the other one. Bad stuff. I would see what the code officer and/or your insurance company says about a 4" pipe with a trap... when added to the existing air infiltration of the structure it might be enough. Not sure you have a choice in the matter, but worth a shot.

cheers

 

[jimdeq]

Correct. There is not a direct outside air connection. Jebatty says 4" pvc is not nearly enough fresh air. Yet from reading posts on boilers in garages and outside buildings some people dont even have fresh air intakes. If 4" is not big enough how big should I go and how do I stop free flowing cold air from turning the boiler room into a freezer.? Also, how low to the floor do I run the PVC and should I insulate the pipe ?

 

[in hot water]

Check with the local code authority, they sometimes amend the National or State codes. Most AHJs use NFPA or the National Fuel Gas Code.

If the EKO is in a sealed 6X 11 room you will need outside air.

In a large room, like a shop, it is considered "unconfined space" and some of the air can be calculated from the room volume.

Your installation, for fire safety is in a "confined" space and may need both a high and low vent to the outside. In many cold weather climates they have rolled back that 1/4" per 1000 rule. But the bottom line is the fire needs enough air (O2) to burn efficiently.

Motorized dampers are sometimes allowed and tie them into the blower circuit so they close when the fire does not need O2. Some leakage will occur to keep the idle mode supplied with air. It takes a lot more opening than you might think is necessary to, keep the fire going. be safe.

hr

 

[jimdeq]

Excuse me if this sounds stupid,but why does everyone insulate there boiler room if they are going to have a 6 or 10" inch hole cut in the ceiling to the attic?

 

[Hunderliggur]

You mean for the makeup air? This is my second season, last year the boiler building was not insualted or sealed. Somehow a tarp does not count as a door ;-) I have a window I can leave open this year in my "sealed" boiler chamber (6x12). The reason to insulate is to keep the unit from freezing when you are NOT building fires, and to minimize heat losses while burning. But you still need air to burn. I am thinking about a "heat trap" between the boiler room and the wood room. Probably a register vent I can close with the cold feed low in the wood room and the supply in th boiler room up high (6 feet). I am also considering a cat door ;-)

 

[djbutt]

I Installed a Tjernlund inforcer fan in my basement boiler room. Its basically a rubber shock mounted squirrel fan in a box with 4 inch pvc to the outside it has a flapper in it so no cold air enters when not in use.

I installed a current sensing relay that monitors the electric feed to my boiler's draft fan. When the boiler's draft fan is on the Inforcer fan is on and when the draft fan shuts off so does the Inforcer fan.

No unwanted cold air when the boiler is not in use and super quiet too.

http://www.tjernlund.com/Retail/inforcers.htm

 

[Como]

That would work very nicely.

 

[jimdeq]

Hunderlugger, Can you explain to me why low in the intake portion and high in the discharge? If I was coming from the attic down into the boiler room at what height would I terminate behind the boiler?

 

[Piker]

I Installed a Tjernlund inforcer fan in my basement boiler room. Its basically a rubber shock mounted squirrel fan in a box with 4 inch pvc to the outside it has a flapper in it so no cold air enters when not in use.

I installed a current sensing relay that monitors the electric feed to my boiler's draft fan. When the boiler's draft fan is on the Inforcer fan is on and when the draft fan shuts off so does the Inforcer fan.

No unwanted cold air when the boiler is not in use and super quiet too.

http://www.tjernlund.com/Retail/inforcers.htm

This is an excellent option to the passive combustion air vents... not only does it lock out cold air when the boiler doesnt need it, but also prevents the effect that the wind has on the high/low pressure side of the house.

cheers

 

[jebatty]

why does everyone insulate there boiler room if they are going to have a 6 or 10” inch hole cut in the ceiling to the attic?

Whether that hole is cut to the outside in the boiler room, or air is provided by the many small to large air leaks in a structure, the result is the same -- what would look like a gaping hole to the outside. That's the reason it is so important to seal unwanted cracks and air leaks, which in many houses is the equivalent of a couple of open windows.

My new shop is a great example of a boiler situation needing air. Unless I open a window, my Solo 40 cannot maintain a good burn. There are not enough natural air leaks in the shop to provided needed combustion air. The standard for the Solo 40 is 150" square, which for a 24" window is 6". I found that about 3-4" is enough, and when the boiler is firing, you can't even notice that the window is open. I do need to remember to shut it, but if I don't remember to open it, the Tarm lets me know because smoke rolls out of the firebox door as soon as I open it, but with the window open, no smoke at all.

 

[Hunderliggur]

Hunderlugger, Can you explain to me why low in the intake portion and high in the discharge? If I was coming from the attic down into the boiler room at what height would I terminate behind the boiler?

I was hoping one of the "heat trap" guru's would chime in, but basically the cold air at the floor level in the wood room is not going to rise up to the ceiling side of the warmer boiler room on its own. When the fire is burning the negative air pressure will draw it in. I believe you can achieve similar results with a "U" trap arrangements but it is a topic that has only been addressed peripherally recently. Any makeup air heat trap guru want to chime in? I have not built my vent yet.

 

[woodsmaster]

[quote author="jimdeq" date="1292219630"]Excuse me if this sounds stupid,but why does everyone insulate there boiler room if they are going to have a 6 or 10" inch hole cut in the ceiling to the attic?[/quote

I'm insulating mine so that if I dont build a fire for a while stuff dont freeze. I'm going to vent threw a window so after the tanks are charged I can simply close the window if I'm at home. If I'm not home then I guess
I'll lose some heat out the widow and not the whole shed. I will automate the venting later.

 

[djbutt]

I tried make up air via heat loops of different configurations and for me they all seemed to be inadequate volume wise and let cold air in all the time, at least in the basement of a two and a half story house, stack effect, negative pressure and all that.

Plus as some have said on a windy day the upwind side of your house will have pressure against the outside of it and the downwind side will be under a vacuum so depending on where the opening is and the wind direction sometimes they work well, sometimes they work against you.

The Inforcer fan, in my scenario anyways, works the same no matter whats going on with temperature, pressure or wind.

Also if your boiler is working well as is, put in any old vent to satisfy the insurance guy. The vent only needs to work if your system really needs it, otherwise it would just be for show. ;-)


Another thing, as a firefighter I can tell you with confidence that an opening between your boiler room and your attic is an absolute no no. It sounds lilke you did a nice job with the sheet rock and fire door.

 

[in hot water]

Hunderlugger, Can you explain to me why low in the intake portion and high in the discharge? If I was coming from the attic down into the boiler room at what height would I terminate behind the boiler?

I was hoping one of the "heat trap" guru's would chime in, but basically the cold air at the floor level in the wood room is not going to rise up to the ceiling side of the warmer boiler room on its own. When the fire is burning the negative air pressure will draw it in. I believe you can achieve similar results with a "U" trap arrangements but it is a topic that has only been addressed peripherally recently. Any makeup air heat trap guru want to chime in? I have not built my vent yet.

A contractor I know in colorado woul bring the combustion air vent from up high down into a 5 fgallon bucket, usually a 6 or 8" round vent depending on the BTU of the appliance. He claimed the cold air would settle in the bucket and act as a thermal trap. I have not tried this, but it is simple enough to build.

Here is the louver I used last season.

I have a motorized skylight on the list of to dos. It would allow some light into the room, aid in smoke removal, and provide combustion air when the boiler fan is running.

hr

 

[bpirger]

Not that this is helpful, but this is something I thought was a big advantage for the Garn design....direct outside combustion air. I can seal up the Garn barn tightly and never worry....not that it is that tight (not at all at the moment!) But it did solve the problem for me. I like the nice control vent setup, and add that to the overall cost. It never seems to end!

The Garn brings in fresh air via a 7" single wall duct...38.5 sq inches and she burns at 300,000 BTU/HR plus (according to Garn).

This is one Garn advantage that is often overlooked.

 

[Como]

The Garn instructions do mention the need for make up air, it was mentioned in a thread a month or so back. I think the logic was to do with the air drawn in when the door was opened.

Presumably a lot less than would be needed by a comparable burn unit.