fresh air intake kit for oil burner:y/n?

Theodore_2

Hi.

My 9year old Burnham MPO147 (147,000 BTU, located in lower New York State) has an optional "fresh air intake kit" (part #611280031 Burnham Air Intake) that consists of a 4" dia metal duct piped to the burner.

I'm making a boiler room enclosure and considering this.

I've read some places that very cold outdoor air temps (i.e. night in the middle of winter) piped directly to the burner in this manner can cause flue gas condensation. My boiler guy's opinion is not strong in either direction (to install vs. not to).

Is this a bad idea to do? Any experience appreciated.
Thanks
Theodore

kcopp

Where did you read that? That is a new one.... If you need combustion air, then you need combustion air.

Robert O'Brien

That kit brings air into the burner cover not the burner itself, between that and the length of piping, it will temper the air tremendously. If you are on the cusp of chimney condensation right now it may tip you over the edge. It depends on your chimney and current net stack temp.

Jamie Hall

I find it very very difficult to imagine a situation in which combustion air temperature at any normal range -- say from -10 F to 100 F -- could affect condensation in the exhaust after going through the burner at.. what? 1,000 F or so?

Except in one possible situation: if the combustion air is concentric with the exhaust duct, and is long enough, then it could. But I don't think that that is what you are talking about.

Robert O'Brien

It will drop the net stack temp by the difference of ambient vs. the outside air supply. By the time that outside air reaches the end cone it won't be that much different from ambient.

Robert O'Brien

The excess air will increase as the air supply temp drops due to the higher density of cold air. This will drop CO2.

Steamhead

In the old days, they would add a few feet of fresh-air duct and/or increase the duct diameter by one size to help warm the incoming air. ISTR having some diagrams of this someplace........

Theodore_2

Hi, I'm the original poster.
Kcopp, Even the installation manual says:

"Using outdoor air in the middle of winter may
result in lower stack temperatures and chimney
degradation. Any signs of condensate seepage
or discoloration at the base of chimney must be
remedied immediately per the details outlined in
this section."

And I've read similar concerns in other online posts elsewhere.

I see you other points (per Robert OBrien, Jamie Hall, etc) that the length of the intake pipe will HELP temper the temperature. I still have to insulate that air intake pipe (to prevent condensation, and prevent general heat loss as this cold air runs through a ceiling joist bay in the basement).

kcopp

Again... If you are closing in around the boiler you really don't have a choice. Gotta have it.
What is the option? Not doing it and have the boiler soot up because it is starved for air?
The next thing to do is make sure the chimney is lined. A Stainless steel liner is probably best.
Most All boilers condense as some point.
If your condenses a bit on the coldest day of the year it will not significantly effect it longevity.
As others have said make the intake longer and have it exposed to the warm air in the boiler room. The other thing you can do is add a Field VRV damper to the intake. Field Controls makes this and it will also use some of the warm basement air to temper the intake.
http://www.supplyhouse.com/Field-Controls-VRV-4-4-Vacuum-Relief-Valve

Theodore_2

Agreed... I have to do SOMETHING to provide air for the boiler if I'm closing it into a room. My other option was to put in a louvered door or build in two louvered "windows" into the curtain wall around this boiler room, with high and low louvers, just as most building codes require a high and low duct or louver into a boiler room. Then it would just pull the air from the "main" part of the basement, as it always has. But this option seems a bit counter-intuitive because I'm doing all this work to put up fire-rated door and fire-rated sheetrock (for code), only to leave two openings in through the same wall (or door).

SWEI

Theodore said:

to provide air for the boiler if I'm closing it into a room. My other option was to put in a louvered door or build in two louvered "windows" into the curtain wall around this boiler room, with high and low louvers, just as most building codes require a high and low duct or louver into a boiler room.

The 'two hole method' may be in the code, but it has never been scientifically proven to work. If the appliance ever backdrafts (especially in cold weather) carbon monoxide can build up to sky high levels in the boiler room -- and it's not very far to the occupied spaces. I would seriously consider a double-acting barometric damper if you decide to enclose the boiler.

Theodore_2

SWEI, To best of my understanding, my existing barometric damper is single-acting. Why do you suggest considering "double acting"? I assume that means it can swing both into and out of the pipe.

All, if I go with a fresh air duct, I have to be concerned about the elevation outside and snow-drifts. Is there any reason why I can't make the duct 4" PVC pipe? This way, I can put a riser on it, and a goose neck, and it will be above the expected snow line. Thoughts?

SWEI

Yes, a double-acting barometric swings both in (to control draft) and out (to detect backdrafting flue gases with a spill switch.) They are required on gas power burners, but still a good idea for any burner. Think of it as cheap insurance.

PVC will insulate the incoming air from internal ambient far more than a metal duct, and a 4" pipe (without a fan) may not provide enough air. A combustion analysis is the only way to know for sure.

Robert O'Brien

Just curious, did you expend as much energy as this decision on the sizing of the MPO? Or was it there when you bought the house?

Theodore_2

Robert, Yes; and I chose the MPO. At the time, although my HVAC guy said I needed a boiler of "about 150k BTUs," I ran my own Manual J calc, which matched his rule of thumb. I respect his experience, but I wanted to check anyway. Given his current ambivalence with the fresh air kit, I really appreciate all of your comments and opinions.

SWEI,
Page 39 of 96 of the installation manual (http://www.ecomfort.com/manuals/v8h_io_manual.pdf) indicates a 4" pipe with no fan. My run is only 10ft horizontal, so I'm comfortable with this specification. What do people typically do to raise the air intake pipe above the snow line ...without looking like a ridiculous house appendage? Thanks for the input.

SWEI

Sorry -- just re-read your original post and see that the air intake is directly connected to the burner. PVC is not going to help warm that air, but a sheet metal plenum could be installed above the boiler to take care of that. There are several strategies for hiding the pipe. Inside the exterior wall is the least noticeable but may not be practical.

A firing rate of 147k puts you somewhere around 125k DOE output. How big is the house?

Theodore_2

My house (not including the currently unfinished basement which will have it's own dedicated heating system) is a 1,350 sqft, 2-story cape cod style house.

KC_Jones

Theodore said:

My house (not including the currently unfinished basement which will have it's own dedicated heating system) is a 1,350 sqft, 2-story cape cod style house.

Why? That boiler has enough output to also heat the basement and your neighbors house and most likely their basement. Most likely the smallest MPO would have been too big for a house the size of yours including the basement.

SWEI

That boiler should be able to heat your house along with the neighbors on both sides (assuming they are of similar size and construction).

I'm guessing you probably don't have natural gas available, but what are your rates for LPG and fuel oil there? LPG boilers are available in smaller sizes -- and for that size house it might make sense even if the price per BTU is a bit higher than that for #2 oil.

Theodore_2

Ok, clarification: vent pipe from boiler to chimney is 6" diameter.

Regarding the capacity of the boiler, I know I've plenty of additional capacity for a heating loop for the basement, but piping to where I need heat is a real pain in the rear due to many obstructions. I've one more zone I can add to my heat pump/AC, so doing so for the basement along with two electric baseboards. It's strictly a matter of convenience to install.