Hi, I have an oil fired boiler in the same room as a clothes dryer. The room is about 11 x 14 x 8 or about 1200 sq ft. I think I need to install a replacement air system for the boiler, especially when they are on at the same time. Previous owners didn't seem to worry about it, but I think maybe they were just lucky. Although I have a CO detector in there now that has been quiet thus far.

How do I go about determining how to wire the fan so it comes on when the burner comes on? Just get out a meter? Where should I start?

Or is the fan not necessary, do I just need a vent pipe from outside that terminates in the vicinity of the burner?

Thanks,

Mike

 

I assume this is a non-condensing boiler.

Many boiler manufacturers indicate that most houses have enough air infiltration (leakage) that an outside air supply isn't required. Check the installation instructions on the web for your model.

If your boiler/dryer room can be shut off from the rest of the house, then inflitration may be insufficient. My boiler room has a door, so I installed an air register in the door. I used the type of register for cold-air returns in forced-air systems - w/o a shut-off damper.

Your boiler is oil-fired. Is your dryer electric? If so, it has no combustion air requirements, but it does exhaust air to the outside. That should be less than the air drawn up your boiler's flue.

If you decide to add an outside vent to supply combustion air, I wouldn't rely on a fan. Better to install a PVC pipe, such as specified for condensing boilers or furnaces. You can surf for the usual recommendations - probably at least 4", two 90-deg elbows at the inlet, and the inlet well above the maximum snow line (including an allowance for drifting).

 

Common problems with a clothes dryer and boiler in the same room aren't limited to combustion air. When the dryer is running, it can 'rob' combustion air from the burner and in very tight homes may even cause the burner to 'soot'... another problem is the dust created by the clothes dryer will be airborne to some extent and get sucked into the burner air inlets. Over time it will deposit on the blower wheel and even plug up the air inlet slots on the air band. So watch out for that.

A laundry room also contains the usual assortment of cleaning supplies. Like chlorine bleach... and if you look at most boiler install manuals they caution against allowing the boiler to breathe these fumes. The chlorides in particular can cause problems... in extreme cases. On the other hand, there are probably MILLIONS of boilers installed in laundry rooms all across the USA... with no problems. But, just so's ya know... I'm just sayin'...

One way to provide combustion air without losing a ton of heat is to install a 'heat trap' air intake. The same way that a 'P trap' works in a plumbing drain system, a 'heat trap' will do the same for air.

You first need to determine how much air you need. In most cases, a 'hole in the wall' the size of a clothes dryer vent is big enough, but do the calculation to be sure. If it is big enough, you would make a round hole in the wall, install a dryer vent exhaust with the flapper removed and an insect/bird/vermin screen replacing it. Run a hunk of the dryer vent tubing up to the ceiling, and then back down again to near the floor in a big " U " shape. Cold air being heavier than warm air will prevent air from coming in unless it is 'sucked' in by the boiler or clothes dryer.

There's a selection of systems on this website:

Combustion Air Systems, Fan-in-a-Can, Airboot Kits, Vacuum Relief Valve, Air Intake Hood - PexSupply.com

"Fan in a Can" or simply a 'boot' on the burner itself. There are 4 and 6 inch items... you may find that you need 6", but I kinda doubt it. The literature for those items may help you determine what you need... I think you can download it from that website.

If you did decide on the 'fan in a can' there would be instructions for wiring with the system. Basically you would tap the 120VAC from the burner connections to run the fan.

 

Thanks Guys, yes it is a non condensing boiler. On that subject, the stack temp is about 650-700 degF (old and due for replacement in the spring). So once it's got the flue nice and hot the barometric damper is really flat out and drawing a TON of air out of the boiler room. Add that to the dryer which yes is electric and there's a lot of air being pulled out of there even with the door open. The house is not tight by any definition. Can't see how I missed that product on pexsupply, I've been on there a ton for a lot of my new boiler research. I will probably do the calculation for the new boiler rather than this one, and this one will have to take what it gets for one more winter. Thanks again.

 

NFPA 54 (National Fuel Gas Code) contains venting requirements for gas-fired appliances, including boilers. (Yeah, I know, your boiler is oil fired, but this info may be instructive.)

If the interior volume of the house that communicates with the gas-fired appliance(s) is at least 50 cu. ft. per 1000 Btu/hr of heat input, then no additional make-up air source is required. (If there are doors or partitions involved, then they need to have grilles or openings of 1 sq. in. per 1000 Btu/hr for the adjacent space to be included in the 50 cu ft per 1000 Btu/hr.)

So, for example, consider 100,000 Btu/hr heat input to the boiler (plus dryer, etc.). That will require 50 x 100 = 5,000 cu. ft. of volume. With 8-ft ceilings, that amounts to 625 sq. ft. of floor area - not a great amount.

According to the same code, a fan-powered outdoor make-up air supply, if it's to be considered as a source, must have the fan supply interlocked with the burner. (I would take this to mean a sail switch in the fan duct - not just the burner and fan powered from the same electrical source.)

The devices suggested by Trooper don't seem to have fans, so they wouldn't need any interlock. But, I think the inlet from outside needs to be well above the maximum snow line (plus an allowance for drifting).

I don't know how the codes would differ, if at all, for an oil-fired boiler. But, I wouldn't think they would be too much different.

Anecdotal observation: Here, where I live, in natural-gas country, most everybody has gas space heating, gas cooking, gas clothes drying, and gas water heating. At my age, I read the obituaries regularly - no asphyxiations that I know of. And outside make-up air is unheard of. (Maybe they died long ago, and their houses have been since vacant?) Your mileage may vary.

 

If the barometric damper is wide open, I think there must be plenty of air supply available. You might want to observe it with both the boiler and the dryer running.

If you were to temporarily cover the air inlet of the barometric damper with a piece of cardboard, limiting the amount of air available, what would happen? The damper would fall shut. Yours is wide open.