How to provide fresh air to my boiler?
 

This might not be the proper location for this thread, but, here it is any way.

I have an 80% efficient boiler. 80% so it's not direct vented. Since I have tightened up my basement I'm going to need to provide it with fresh air or it will be less efficient and it will start dumping CO into the house. I could pay the HVAC guy to do this but 1. I don't have money and 2. it can't be too complicated. Does anyone know how to go about this? DO I just run an open PVC pipe or something like that through the wall up to the burner? That would be one big hole for air to leak into the house.

For the moment it eludes me, but I think there is some issues there with condensation and the heat exchanger not being able to handle the water... I just can't remember exactly what the problem is right now.

Huh? Heat exchanger? Maybe you know more about this than I do but as far as I know all this entails is running a tube of outside air right up close to the burner of the boiler. Although I could see condensation being some type of issue in the warmer months when the air is capable of holding more water. Especially in this swamp where I live.

I'm in the same situation, though my basement is as leaky as a sieve, and I haven't anything about it to keep air going to the boiler.

So, I can see a few possibilities:

1. Make a vent in the wall. This will pretty much undo all of your sealing efforts.
2. Deliver outside air through a PVC pipe to the burner, as you proposed. You still have a hole-in-the-wall situation, but at least the burner is sucking in colder air. This is usually good, but in this case it may turn out that your boiler is tuned to intake air @ room (basement) temperature. When the burner is off thn you are still getting a rush of cold air.
3. PVC pipe with some kind of damper, which allows fresh air in only when the burner is fired up. This would be ideal, but the valve actuator would have to be failsafe. Or maybe not - if the valve doesn't open, then a CO sensor should let you know.
4. Upgrade to a boiler with a closed combustion chamber. These are more efficient (90-95%, 107% for condensing models), but are very expensive.

I have a pellet stove wood burner, it has an external air tube to the fire box. This allows the air to be sourced external to the building; if the building is a mobile home or otherwise tightly sealed. The instructions say if it is used, then run an external metal pipe through the wall 1 5/8 dia and join to the fresh air tube leading to the fire.

Not sure how your boiler fire works, but if the fire box has a forced air fan like the pellet fire, then the hole in the wall isnt very big compared to the size of the room, so any ingress of cool air into the room would be minimal.

Cheers
Mike

Haha, I remember now what I was thinking about. It was if you have condensation in a non-condensing furnace on the heated air side, not the burner side. That becomes a problem and can corrode the heat exchanger and cause problems. A dedicated intake shouldn't cause that problem. I knew something wasn't right there. :)

The woodstove at my old house had an external air intake. I believe they are required by code on new installs these days. It was a 6" metal duct if I remember correctly. The tube got very very cold near the wall and was quite hot near the stove when the fire was lit. Also I could go outside and was shocked just how much air that thing was drawing in.

In that install the tube was maybe 16" long. My new house I would love to add something similar but I have no way to get the air over to the insert.

Well these stoves are built for this kind of thing. My boiler just has some lovers on the front down near the bottom. There must be a way to make a fairly air tight baffle that opens when the burner fires up. I wonder how professionals do this.

I'd guess that professionals don't do this unless the furnace/boiler is made to do it off the shelf. In that case I'm sure the furnace/boiler has some duct piece attached to it and they just run plumbing (probably PVC) to it.

To do it yourself you're going to need to seal up the boiler's intake area completely. Then you need to punch a hole in it and run some ducting to it (PVC is probably fine). I'd add a damper or two in there to prevent air movement when you don't want it. Alternatively you could hook up an electronic damper that opens when the furnace turns on. I'd try to keep the ducting short and throw some insulation around it when you're done.

The HVAC guy I deal with told me that he'd run a duct of some kind right up to it. So this isn't abnormal. There's no real way to seal any of it up. The louvered cover is really nothing more than a metal plate that pops on the front of the thing. It's open all over the place. I have an energy audit scheduled for 10-10 so I probably need to get this all squared away before then. This might be a stop work condition for any contractors who might be doing work here.

I figure a damper similar to one on a gas water heater should work. It would work best to seal the inlet to the inlet chamber but I assume that if you do that you would need to calculate the amount of air that the pipe would need to be able to supply. I would also assume that you do not need to seal it but place the opening close enough that the majority of the air will come from the pipe.

If the area by the burner gets hot you should not use PVC as it gasses off when it heats up and for the last foot or so you might want to use metal. Make sure that the opening on the outside will not get covered by snow or debris that could block the flow of air and adding a screen to keep critters out would probably be good.

Can you get a picture?

http://i182.photobucket.com/albums/x...s/IMGP2098.jpg


http://i182.photobucket.com/albums/x...s/IMGP2097.jpg

You see the cover just hangs on there. There is nothing remotely sealed about it.

Yeah that is going to be a bit of work to seal up. You can do it, but its going to be a pain. Perhaps you can add some sheet metal in there? Just bent some pieces to fit in there, bend flanges on them and screw them to the outside sheet metal. Seal it up with some silicon. Add some weather stripping to the cover as best you can. It doens't have to be perfect, just the better you seal the more it'll suck from outside vs inside.

What I've seen is the intake duct has a slight slope down to the outside, so that any condensation that forms simply runs to the outside, the pipe turns down via two 45's at the boiler. And as far as connecting the intake air duct to the burner, I think that if it is simply as close as possible to the louvers, it will actually supply outside air to feed any convection flow that may set up after combustion stops: when combustion stops the warm walls of the exhaust flue will draw warm room air up and out, so if outside air is available right there then it will likely flow into the appliance. The pressure balance is so subtle that you you may want to consider prevailing winds and so on. Also, consider the possibility of things like auto exhaust, opening the basement door at the wrong time may pull fumes in with the outside air.

Good point about condensation there herlichka. But, how do I air seal the duct?

Well, google helped me find this.

I wonder if I can get these in the US and how much they cost.

EDIT:

Well Amazon has it all!

I don't know if you really have to, or want to seal the duct to the appliance, doing so would constitute a "modification" to the appliance, and may present a liability issue: Various inspectors (municipal building inspectors, gas company, Fire Department, Insurance companies, etc) are trained to look for these things.

I have seen a number of woodstoves where the manufacturer's instruction manuals illustrate the duct presenting combustion air near the air intake of the stove, but not physically connected to it.

Yeah. I'm not planning on trying to convert it to a direct vent apparatus. The boiler is just open everywhere. Everywhere.

I'll just deploy that thing previously linked to at the end of a 6" insulated flex duct right next to the louvers on the front panel.

I wonder if you could modify a drier vent with some weights,
http://i46.photobucket.com/albums/f1...Solar/z002.jpg
so it would be closed pretty tight, until there was a pressure drop in
the basement, which would cause it to open and let in some outside air?
(This pic is of a bathroom ceiling vent that dumps into the attic).


I was thinking of running some 2 or 3 inch PVC from the outside, over beside the oil burner.
If it turned out to be venting in some really cold air all the time,
then I would build something like the drier vent.
Weight down the hatch, until only the burner coming on would lift it.
(Unless my basement is really leaky)!!

We stopped heating the basement a few years ago. The geothermal effect
of the ground water flowing under the basement slab, keeps the floor
above 60F during the coldest winter days.
Just keeping the old single pane windows closed keeps the basement
between 60F and 65F all winter. (With some help from boiler heat loss).

Should be interesting this winter, when I plan to start using the exercise
equipment down there every night.. :eek:

So they actually sell those? I was thinking about making one myself. The linked device's fail-safe mechanism requires energy to keep the damper closed when the boiler/furnace is off, any idea about how much energy?

As for sealing the furnace, I took a closer look at mine, and here are some pics:
I have a hanging model (Ariston Genus 23RI), no louvers, only a small peephole to spy on the flame, but the whole bottom, top and back are open.

Inside is the combustion chamber, plus all the gizmos and doodads in the bottom section.

Now, imagine that the whole boiler is boxed in and an intake tube with fresh, cold air is hooked up. That air will be steadily flowing through the boiler and out the chimney. If that air is really cold, like as low as -30°C (-22°F), then the whole inside of the boiler will freeze, both the electronics and the water pipes.

So maybe only the combustion chamber can be sealed off?

Mine is totally open at the bottom, under the burner, and at the top, where extra basement air can be sucked into the chimney to mix with the exhaust.

Sealing the combustion chamber may potentially freeze up the heat exchanger, unless the intake tube had a damper mechanism (cold air is probably OK while the burner is fired up).

OK.



This thread is getting beyond the scope of what I originally intended. This is not a bad thing. Since I have discovered a valid, safe and air sealed method of providing air to an atmospheric boiler under conditions which it was not intended to operate (such as a well sealed house) any further speculation is in strict modder Territory.

Can one convert an atmospheric boiler to be a sealed combustion boiler? This is the question we are raising here. Aside from simply creating a sealed box around the unit there are certainly many, many, MANY more issues to take into consideration. If people are interested, let's hash them out.

Piwoslaw:

It is my personal opinion that your concerns about freezing are unwarranted due to the fact that there is a lot of heat present at all times. Either active or residual heat from the boiler itself or from the surrounding environment that will nullify this. Now if you keep you mechanicals in an unconditioned space (and if so you have better things to worry about than upgrading your functional boiler to a sealed combustion boiler) freezing might be an issue. From my point of view it is next to impossible to remove an entire basement from the thermal envelope of a house. It's more expensive, but, one should include it. You gain conditioned space and saves money on utilities.


Next:
Is it actually possible? Are the burners different in some way? I’m assuming the 97% efficient burners aren’t the same as the 80% efficient ones in a different box.
I know someone who. For the first decade of the operation of Buderus in the US was their troubleshooter. He did all of the Buderus training in the early 90’s. They flew him all over the place to troubleshoot new installations. He very well may be the most competent Buderus tech in North America. I’ll contact him ASAP about these issues.

OK, I searched for pictures of the insides of boilers to see the difference in hardware between open and closed combustion chambers. Here is a good comparison:
Notice the closed model on the right: The combustion chamber itself is not sealed, but instead is inside a sealed box, with the rest of the plumbing, motor, electronics outside the box. I think this is the way to go: seal the upper half of what is inside the boiler.

While searching I also noticed that all models had intake and exhaust in a concentric tube set-up (with the exhaust inside the intake), I didn't see any which would have the intake come in from a different side than the exhaust. Other than safety, maybe this to pre-warm the intake air?
This concentric intake/exhaust tube can either go vertically up a chimney, or horizontally out through a wall.

Also, all models had a fan for ventilating the combustion chamber. This fan could also act as a damper to hinder airflow when the burner is off, though with a totally sealed chamber this shouldn't be a problem.
I believe (though I am not sure) that a Rheem model has two fans: one for the intake and one for the exhaust:confused:

Now, once the combustion chamber is closed up it will be very temping to take the next step and convert the boiler to a condensering model increasing the efficiency by up to 15%. The problem for a DIY'er would be a good, acid resistant condensing heat exchanger. The commercial HXs are made of 409 stainless steel, from what I've read.
But 'condensifying' the boiler is worth its own thread.

S-F, I'm very interested in what your Buderus friend has to say.

Well, here's the reply from my friend:

Sounds like it's not possible. I'm not sure but judging by his statements it would seem as though it has something to do with air pressure.

Thanks S-F:)
I was starting to see potential problems with just boxing in the combustion chamber. For example, a fan would be needed to keep the fresh air flowing in, but it would have to compensate for different burner flame sizes (my boiler's burner adjusts the flame between 11-23kW) - too much air with a small flame could be wasteful and/or dangerous.

Replacing the innards with those from a closed chamber model probably wouldn't be cheaper than buying a new boiler.

So a pipe that ends right under the boiler it will be. But the damper which closes only when the flame is off should be OK?

How to provide fresh air to my boiler?
 

Hi,I don't know much but would suggest you to take the advice from the expert.