Old Boiler, Combustion and Co2

Let's get the nomenclature correct. CO2 is a percentage measurement of Carbon Dioxide and CO is a PPM measurement of Carbon Monoxide. I'm assuming you mean CO.

Your first tech is not a professional technician, just a hack salesman. Same goes for his company.

If he's reading 7ppm CO in the flue you're fine. In fact with proper combustion you could read 0. I'd like to see the rest of the combustion numbers.

Now if he's reading 7ppm in the room, now you need to investigate.

If it's a boiler, then some of the reasons for high CO are poor combustion, not properly cleaned, blocked flue pipe, leaking door/burner gaskets.

debbyg said:

I had it cleaned and at the end of the appt, the tech checked the CO2 reading and he got 7ppm and told me he needed to turn off the boiler and recommended we replace it.

Crap

debbyg said:

I had another tech from a different company come out today, his first concern was the need for fresh air in order for proper combustion to occur, and he said it is important to keep the small vented window in the enclosed boiler room open, so that the needed air wasn't being drawn from the room, but instead was being drawn from the outside... When he took the CO2 reading with the window open it sat between 0-1ppm. He also stated that older boilers may emit a small amount of CO2 over time, due to age.

Again, are we talking about CO or CO2? At least tech #2 is thinking. Never heard of older boilers emitting small amounts of CO (sic) over time, due to age. I've heard of combustion getting a little less efficient.

debbyg said:

When I called the first company back and told them the reading was 0-1, they stated it was only because the window was open, bringing the fresh air in, and if we closed the window, the Co2 level would most likely return to 7 or above.

More crap. Tell them to come out and prove it.

debbyg said:

So here lies my dilemma and questions-
+Is the fresh air from the window required for proper combustion?
+Is the fresh air from the window somehow masking a higher level of Co2?
+Is an older unit with a CO2 reading of 1ppm safe or should it be replaced?

1. Yes. Proper amount of air is needed for combustion. This is known by doing a little math regarding the firing rate of the boiler, and the cubic feet of the room (the available amount of air for combustion). If it's not enough, then you would need to introduce more air for combustion. Also, if your boiler is in the same area as a high efficiency dryer, that dryer is sucking all the combustion air out of the house (let alone the room).
2. No, again CO, not CO2 However, if the room were running out of combustion air as the boiler was firing, then yes, CO could rise. But unless you're in a very small room, you wouldn't notice it in 10 minutes. Or, like I said above, a dryer or even an exhaust fan can change the pressure of the room, affecting combustion and draft.

So to sum up, determine the amount of combustion air needed, including factors for infiltration, exhaust fans & vented clothes dryers.
If it's not enough, opening a window would help, but bringing combustion air right to the burner would be best.

Sounds like it's time to invest in a decent CO tester & meter and investigate the potentially dangerous situation yourself...

https://www.amazon.com/Tough-Waterproof-Made-USA-Monitoring/dp/B004YUEPBW/ref=sr_1_8?ie=UTF8&qid=1508977872&sr=8-8&keywords=sensorcon+inspector

Combustion air is measured by measuring draft. You can't pull air out if there is no air to pull in. Just having openings does not guarantee combustion air is getting to the equipment. However oil burner have a fan a suck plenty of combustion air.
If there is CO in the closest it might mean the flue or sections are restricted but then you would probably have a smoke smell. Some hand held CO detectors are heat sensitive and will read CO just because of heat and shouldn't be used near a heat source.
It is always better to check around and in the equipment with a combustion analyzer. These are used by professionals. Hacks don't use them!!!

There is no way a gasket leak will produce 325ppm of CO. However, a boiler not venting properly will cause a gasket leak from stress and heat. I am betting that a combustion test on your boiler would have shown CO in the thousands of ppm range. Hopefully repairing the gasket was not the only repair.

My question is why was the boiler making 325 ppm of CO in the first place? Not from a gasket leak.

With a 5 x 10 boiler room with a water heater and a boiler and no combustion air opening, window and door closed equipment operating I would be surprised if you could get 0 Co ppm in the boiler room outside the flue

You will positively have Co in that room with no make up air. Equipment running will pull the room into a minus condition until one of the flues starts to backdraft.

Best bet to keep from freezing the room is a small permanant opening sized for just the water heater. An additional opening with a damper with an actuator with an end switch wired to the boiler