I don't know what to tell you unless it's to switch CO detectors. If you can smell exhaust the detectors should pick up CO. Maybe the odor is coming from something else.

You might be able to smell plenty of flue gas without triggering the CO detectors. A properly functioning boiler won't make much CO. If I remember my numbers correctly, a residential CO detector will go off with with longish exposure to 100 ppm. A boiler operating correctly will produce less than 200 ppm. You'd need two rather bad failures in combination to set off a detector, an incredibly bad flue gas leak and a bad combustion process.

OP, is this boiler oil- or gas-fired?

It is an oil-fired boiler, a Utica brand, model TRB-3.

"It is a direct vent and the vent is located about 2 feet of(f)the ground between 2 windows."

Do you get any snow in your location? I would be very worried that a snow drift might block the exhaust. That would be very dangerous.

Why was the vent put out the side of the house and not the chimney? I am not oil burner expert, but I think black soot will eventually collect on the side of the house. Was a permit filed for this installation? It is hard to believe installing the exhaust below two windows which can be opened is not a code violation. You need to have someone look into this.

An odor would indicate to me there is poor combustion and ventilation. If the original installer can't figure this out then hire someone who knows what they are doing. Don't rely on CO detectors to tell you there is a problem.

As I write this it is snowing hard and we've got about 6" of snow on the ground. I'll be shoveling when the rate slows down, and clearing away from the vent is my first step.

I don't know why the builder/owner elected the direct vent option. It does leave soot on the siding, and it does not clean off. There is no chimney in the house. I specifically asked about the vent placement before purchasing -- both the home inspector and the burner tech said it was not ideal, but did not violate the local code. The codes elsewhere, or the uniform code may be different.

For now, I'd like to get to the bottom of the exhaust smell. As we plan on making this a rental property eventually, I may seek a different venting solution eventually. I suspect it will be challenging due to the boiler location and house floor plan.

Direct vent flue location can be challenging when installing a replacement for an appliance that vents in a chimney. In this case, apparently it was not addressed properly when the home was designed.

The DV boiler manuals, that I have examined, are clear about what needs to be done in snow areas. They direct that the outdoor vent and intake are above any potential snow accumulation.

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Vith, that is an interesting thought! There is fiberglass insulation stuffed in along there now, but I suspect there will be room for improvement! Is this area a candidate for low-expansion foam in a can?

I know the burner tech just checked the exhaust and re-hung/tightened up the pipe to reduce noise. I would hope he checked for level then, but I will do so myself as well.

The windows are in good shape, they are all wood interior/vinyl-clad exterior Anderson casements. Compared to my previous 1881 Cape, this house feels extremely tight, especially the living spaces. Holiday vacation plans include insulating pipes and general basement organizing and building a workshop, I'll be adding air sealing the rim joist to the list.

I am so grateful for the collective wisdom and willingness to help I find on the GW Forums. I have learned so much from this group over the years! Thank you!

I checked the exhaust pipe last night. There is a very slight slope toward the furnace. Do I need to increase the slope? It is a short run so I'm not sure how I could accomplish that...

Edit: Misinformation

The slope is so condensed water will run back to the drain for the furnace and not outside the house. I don't see how a wrong slope would make stink inside the house unless water trapping increases pressure significantly within the flue.

Please do a little research on sealing rim joist. I don't know what kind of spray foam you are considering. Lots of foam shrinks and could eventually leave you with gaps. I believe that I've seen advice to use foam board and caulk as a long-lasting approach. I've never dealt with a home with that kind of construction so I did not pay that much attention.

Here is a link to what I believe are the installation instructions for the Utica TRB boilers.

The web site states it has an efficiency up to 87% so I don't think there will be any condensate in the exhaust vent that needs to flow back to the boiler. As a general practice the exhaust should slope upward away for the boiler to allow the hot gas to rise and escape. The instructions make no mention of any slope which I find unusual.

The instructions specify how the vent pipe should be connected to a chimney. No where does it talk about venting out the side of a house. Again I am not oil fired boiler expert, but in my opinion your installation is a bad idea. I could image a strong wind blowing against the house could cause combustion gases to not exhaust properly. This may be the reason why you smell the exhaust gases.

I don't want to alarm you but I think you potentially have a dangerous situation that needs to be addressed. I strongly recommend you hire an expert to review what you have and make the necessary fixes.

Edit: Misinformation

"It is an oil-fired boiler, a Utica brand, model TRB-3."

Here is the brand and model number. The exhaust from a oil fired boiler would be very hot. I don't think PVC piping can be used.

My apologies, you are correct. I am thinking the slope may have a factor, the installation instructions say 1/4" per foot. I am not sure how well they did the air intake either. Hopefully it is insulated so the cold pipe does not condensate similar to a cold glass of water. The boiler itself does not normally allow for horizontal flue, but using their direct vent accessories and making the combustion a sealed system allows for the horizontal application. The reason they had to use that is because you dont have a conventional flue, and making one to achieve the clearances required would not be cheap or easy.

So long story short, they need to ensure that the air intake and exhaust are sealed properly and have the slope correct. I am guessing there might be a leak somewhere in the flue causing the smell. It has to be sealed very well because it normally is not meant to run horizontal for long lengths.

Only way to solve the exhaust interfering with open windows is to relocate above the windows, or elsewhere away from doors and windows.

Clearances and Direct vent instructions

Boiler manual

I read the boiler installation instructions again and agree that direct venting is allowed. There is one sentence which tells you have to read the additional instructions.

Note that the minimum distance from an operating window to the vent is 4 feet for US installations. That distance seems to small to me. Interestingly in Canada the minimum is 6 feet.

"So long story short, they need to ensure that the air intake and exhaust are sealed properly and have the slope correct. I am guessing there might be a leak somewhere in the flue causing the smell. It has to be sealed very well because it normally is not meant to run horizontal for long lengths."

Thank you all for this information. I have a tech coming in this afternoon to look at it. I rummaged around in the pile of paperwork that cam with the house and found the installation instructions for the furnace and vent kit, which I'll give to the tech.

mike_home It seems crazy to me to have it so close to opening windows! I am hoping we can come up with a better solution long term, although it might mean selling before the Uniform Code is adopted.

Would it be feasible to add a different water heating method, eliminating the need to run the boiler in the summer?

You might be well off with an electric tank for DHW depending on oil and electric costs.

Upon deeper inspection, the burner tech discovered the piece of the exhaust going through the foundation, which was cemented into place, was completely rusted. In addition, when the furnace was replaced, the vent fan was not. So this afternoon, the whole shebang was replaced.

Thanks again to you all!

Glad it was resolved without injury to anyone. Someone said vent to air intake distance in Canada was 6,' I thought it was 4,' but a quick google suggests 1.8m/6' in Ontario, but I also saw mention of 3m/10' so I'd go for that.

Op's situation wouldn't pass muster in most places if they were opening windows, but I'm not sure if fixed windows would be ok or not. I certainly wouldn't do it that way.

Well, on Dec. 15 the vent piping and fan were replaced to the tune of $1650, yet we are still getting exhaust smells in the basement and sometimes on the first floor. It does not appear our service company knows how to correct this problem, I welcome ideas about how to solve it!

Who should I call? A different service company? A mason/foundation expert? A new boiler installation company?

In the meantime, I purchased an additional 2 CO detectors.

Also, I have noted I can see light around the vent pipe where it exits through the foundation wall. Can this be the problem? If so, can it be fixed with expanding foam that is fire-resistant (if there is such a thing)?

Pictures of the system and vent (flue) ductwork would help. Rereading this my first guess is they didnt actually seal the joints. Thinking of a different post recently, it is not common practice for them to think about sealing flue joints but with this pressurized direct vent system they need to, the long horizontal run would be another indication for sealing.

Either with furnace cement which requires taking the flue apart and applying while putting it together or using a high temp silicone with it in place. This is the best stuff I could find with good reviews. https://www.amazon.com/Rutland-600-Degree-Silicone-Cartridge-10-3-Ounce/dp/B001GP3AE6/

You do want to seal around the foundation penetration. Critters, insects and cold air can get in. The high temp caulking would work for that as well.

Is there anything to protect the vent and intake from touching the foundation wall? It appears you had corrosion there in the past and would probably happen again. If you can get the caulking between the ducts and the foundation that would probably suffice.

I will take some photos as soon as I can be home while there's daylight and no shoveling! For now, I'll be trying to get a few tubes of that caulking somewhere locally.

Currently having a similar issue with a dunkirk boiler, did you find anything out?

William, We ended up using the high heat caulk recommended above. We basically crammed every spot that looked like it might be leaky with the caulk. Not pretty, but it did solve the problem.

Have you checked the state of the exhaust ducting? I was told the exhaust gasses are very corrosive, thus periodic replacement will be necessary.

In my experience, I will never buy another house with this type of furnace system/set-up. It is loud, the vent is hideous and stains the siding, and I can smell it all summer when I'm outside. Inside I keep the windows on that side of the house shut.

In my dreams, I'll be building a super-insulated/passivehaus as soon as the lottery check arrives.