Control for outside air into basement based on boiler firing

snugglez

I'm not sure I have the best category, or if this has been answered already. I searched around but wasn't sure what exact words to use.

I have a few steam boilers I maintain in a multifamily house. I have air sealed and insulated the house, but when any boiler comes on (and especially when they all do) any place in the house that isn't perfectly sealed from the outside starts sucking air. This makes sense because the boilers use inside air for combustion and the exhaust is vented out the chimney.

My question is: I'd like to install a damper in the basement that opens *only when one or more boilers are firing*. Is there a word for this type of damper (eg "makup air damper" or "boiler room combustion vent damper" only, you know, something less dumb-sounding).

I do not want something that is open at all times, and in fact I plan on using insulated duct right to the boiler area of the basement so when they come on the air gets sucked right to them and I don't get huge mixing of cold air and the warm air (the basement is inside the insulated envelope).

If someone can Id the name (or link to an example of) the thing I want I'd really appreciate it.

Thank you!!

snugglez

Ok literally right after I posted I saw a word I think applies here:
"barometric." So what I think I want is a damper to the outside with a critter screen, and then I'll install 6" or 8" insulated pipe (as appropriate for the size of the boilers) pipe over to the boilers. I'll install a barometric damper inline so that when there is no negative pressure in the house, the damper will remain closed.

Is this a sensible solution or is there something better.

snugglez

I found a video of a guy describing what I think I want. Actually seems even better than what I was planning because it is connected directly to the burner. Maybe I'll call in an HVAC guy.

https://www.youtube.com/watch?v=F1Mx5mtyeQA

I'm in Boston area. If there is someone in that area that has had similar work done I'd love to hear about it and who you used.

ScottSecor

We work in a lot of commercial buildings that have fresh air louvers for that provide outside air for combustion. In some cases the air dampers are fixed (always open) and in other cases there is a electric motor that drives open and closes when the burner cycles. On these jobs with the automatic dampers, there must be an end switch that sends a signal to the burner that it's safe to fire. The idea is that IF the damper does not open there may not be enough air for combustion in the boiler room and the burner could starve for air (and possible give off carbon monoxide gases).

That being said, in some homes or on some small commercial jobs we've installed fresh air duct-work for the boilers/burners. Most of the time it was because the air volume in the boiler room was inadequate or it was contaminated (clothes dryer, chemicals stored nearby, etc). As you may know on most high efficiency hot water boilers fresh air for combustion is almost always "piped in" from outside.

If you choose to use fresh with duct-work for combustion with a electrical damper, I urge you to also install an end switch that will allow the burner to fire only when completely open. As you tighten up the envelope of the home you may actually find that the boilers struggle to gen enough "room air" for combustion. We've installed tons of residential boilers over the years and only had one inspector fail us for inadequate fresh air for combustion. It was a large house with a small boiler room and the door had no louvers. The inspector calculated the room size and mentioned there simply was not enough air inside, we were forced to run a metal dryer vent from outside. It passed inspection and is still operation some twenty five years later.

snugglez

Thank you @ScottSecor! Yep I think the house is leaky enough now that there is enough air to supply the boilers, however--as you said--as I tighten it up it may not be, and it also just makes sense to me to provide a pipe right to the boilers so that even when they are off if the chimney is still drafting the air going up the chimney won't be all the nice warm air from the house but just fresh air coming from outside.

Essentially it seems what I want is what the new-type boilers have: a closed loop supply/exhaust system for combustion. Incidentally, the kits I'm seeing online appear to all have a vacuum override inline that allows the boiler to draw from the basement if the outside air ever gets blocked, so your point is well taken.

Thanks!

ScottSecor

Your idea of a barometric damper may work just fine. They are very reliable, allow air from the basement if required (in case outside air was blocked for some reason), and not too expensive.

ScottSecor

@snugglez I did not notice if you boilers are gas or oil fired. It makes a difference on how to "pipe in" the make-up air.

On another note, we used to do much more oil than gas, that switched about twenty years ago. I'm almost certain some oil burners have a built in fresh air damper on the burner. The purpose was to prevent heated air from the basement from rising through the boiler and out the chimney. You might already have this if you have oil? Others from this site might be able to offer more information.

HVACNUT

You're not only interested in barometric relief. That's the swing damper in the pipe in pic. You need outside combustion air, which that pic shows. What brand burner?
There are kits that connect directly to the burner or look at "Fan in a CAN" this will bring combustion air into the equipment room only when the burner is on.

STEVEusaPA

If you're sucking in air, you need to properly provide combustion air, especially with multiple units.
I wouldn't count/hope for 'leaky enough' without doing some calculations and using a manometer.
The barometric relief is only if the intake get's clogged, then you're back to using the air in the room.
I would definitely wire in air proving in that situation (or use Carlin's new primary in which you can enable that option), or go 'Fan in a Can' like @HVACNUT said wired properly to prevent any boiler from operating without mechanical combustion air.

snugglez

ScottSecor said:

@snugglez I did not notice if you boilers are gas or oil fired.

I have two oil and one gas. The oil burners do appear to have a place to attach a fresh air unit like the one in the video I linked to. The Gas is a burnham independance IN3 or 4, and seems to be designed to just suck in air without much control. I'll look more carefully at it but it's not obvious where I would attach its own pipe.

In the end what I'll probably start out with is putting in a vent to the outside with a simple barometric damper that will let in air when there is negative pressure in the basement (like when the boilers are going). I'll pipe it close to the boilers and see if that resolves the sucking I'm getting all over the house--likely it will.

I'm pretty sure that is essentially the simplest, cheapest, and most reliable method. Get the air source near enough and there will be relatively little mixing with the conditioned air compared to just sucking in from under the leaky front door mailslot, anyhow

If that works I may pay someone to hook up the specialized units pictured in the video to my two oil burners, but I'll start simple and go from there.

Thanks very much

HVACNUT said:

You're not only interested in barometric relief. That's the swing damper in the pipe in pic. You need outside combustion air, which that pic shows. What brand burner?

There are kits that connect directly to the burner or look at "Fan in a CAN" this will bring combustion air into the equipment room only when the burner is on.

I will look up the burner brands, but thank you for the fan in a can suggestion--I'll look into that.

STEVEusaPA said:

If you're sucking in air, you need to properly provide combustion air, especially with multiple units.
I wouldn't count/hope for 'leaky enough' without doing some calculations and using a manometer.
The barometric relief is only if the intake get's clogged, then you're back to using the air in the room.
I would definitely wire in air proving in that situation (or use Carlin's new primary in which you can enable that option), or go 'Fan in a Can' like @HVACNUT said wired properly to prevent any boiler from operating without mechanical combustion air.

Good advice. I think I'll start simple with just providing a new source of fresh air as close to the boilers as possible to reduce mixing of the conditioned air. When I want to get fancy I'll follow your advice for sure.

STEVEusaPA

Even with just a hole in the wall you need to calculate the total btus of all appliances for combustion air, and account for anything else pulling air out of the room like clothes dryers, and exhaust fans.

John Ruhnke

I am going to talk about doing this from an energy efficiency standpoint. I have posted here on the wall many ways to reduce your fuel bills and co2 usage. Often its 2% here, 3% there combined with 7% by doing this and at the same time you get another 8% for avoiding doing something bad. It all adds up. All those little improvements sometimes can add up to giant savings! Lets talk fresh air to burners. I see some big savings available here at times!

A auto air damper piped directly into the burner with a shut down feature while the burner isn't running is very efficient.

First off there have been some studies done in the past that according to the code the fresh air intakes and outtakes cut for the room are way oversized by a large margin. Jim Davis who teaches for the National Comfort Institute pointed this out one day in his class. So just following the codes and cutting two huge holes into the outside wall of the boiler room is just as bad as leaving a door open to the outside. The cold air robs all the boiler room piping and the boiler and hot water heater of a lot of energy. Plus it turns those inside boiler room walls much colder. So now we have some cold walls in the boiler room that is colder than the room next to it. Those walls absorb heat from the rooms next to it. Without cutting outside grills the boiler room walls are hotter than the room on the other side and give off energy to it.

I want to point out that CO is deadly and that nobody unless they are a licensed heating contractor should be taking on this job. You must have enough training to know what you are doing. You cannot just remove fresh air inlets, you can only move or replace them with something else.

Oil fired boilers have a easy solution to this by piping a outside air intake kit directly to the burner. This assures the burner is getting the right amount of air it needs. Being tied in directly means to much air will cause a lean condition. So it pretty guarantee's not to have to much air going to the burner. It is much harder to do this with a gas fired unit.

A mod/con boiler or instant hot water heater have fans and piping to take in outside air. Also gas fired units have direct vent options.

Another option is to cut a louver into the inside boiler room wall or door. When calculating fresh air requirements often the boiler room is to small. Instead of cutting in holes to the outside, another option is to cut holes into the room next to the boiler room. I have done this where a large basement room combined with the boiler room match the fresh air requirements by code.

snugglez

Hi John, thank you for the detailed comment. I am definitely not going to be closing up any fresh air to these units on purpose. What I want to do is shift *where* they are getting the fresh air from.

Currently they are in the middle of a large basement that is conditioned space--that is, the basement is not insulated from the rest of the house, and the perimeter is air sealed. So currently the boilers are creating negative air pressure in the basement, and the rest of the house is more leaky than the basement, so I'm getting fresh air sucked into living space because that living space is very difficult to air seal vs the basement.

My thought is to simply create a vent to the outside in the basement that brings outside air as close as possible to the boiler area so when they create a negative pressure, the vent in the basement will supply the air and there will be far less mixing of conditioned air and the living space will feel less drafty.

To insure that conditioned air is not able to escape back out that new hole, I think ideally the damper would have a trigger to allow the burner to turn on only when it's open, but at the moment even if somehow the damper was stuck closed the worst-case would be a return the the existing drafty house feel, not a dangerous low-air situation as you described.

But as I tighten up the house I will be careful to consult an HVAC pro that can install the correct and safe air supply.

Thanks!

mikeg2015

Barometric still Means the basement is negative and wind Can blow it open til.

I just installed a 24vac 6” powered damper wired to the TT call to the boiler control. my basement is hardly tight and it’s 8-1/2’ ceilings and 1700sqft so I think I’m good.

I ran the duct down near the floor so theres no risk of frozen pipes since 1/2 of my plumbing Is in the boiler room.