advantages of venting a CI atmospheric boiler through the chimney instead of power venting through s

john123

I am considering buying a new CI Weil Maclain boiler and am trying to decide whether to get one that power vents through the side wall or one that uses the current ss lined pipe in the chimney? There would be no problem with the side neighbor either. Would there be any advantages in venting up the chimney?

Jamie Hall

simplicity and reliability

EdTheHeaterMan

WM's CGa
Less moving parts. ++++
Constant draft is sucking heat out of the home - - - -
If equipped with a vent damper, then there are less draft taking heat up the chimney +++++
If equipped with a vent damper, then more moving parts - - - - -
I believe the CGa series has to be chimney vented while the CGi can be vented either chimney or side wall
The CG casting has been around for almost 50 years and is a proven workhorse with only minor changes

bburd

No extra electrical and mechanical components to break down, leaving you without heat until they are repaired.

No smell of oil fumes in your yard or your neighbor's.

Less expensive.

Quieter.

If you already have a sound chimney with a stainless steel liner I can't think of any good reason to go with sidewall venting for a conventional boiler.

jimna01

I inherited a house with an oil furnace with a side wall power vent (we rented it out most of the time).  I like oil and my house is heated with a conventional three pass chimney vented boiler.  It’s trouble free  , odor free and just works simplicity   That power vent was a pain in the butt. Basement smelled of oil after shutoff ( mostly eliminated my installing an air intake boot) .  The biggest problem is the thing croaked about every 4 years which typically cost over a grand to replace and usually took 3 to 5 days to get a new power vent.  Get the chimney and save yourself major headaches

john123

thanks for your comments all
I never had any problem with a power vent but that info jimna01is very helpful. It's what I think too.

SuperTech

I can't think of one good reason to go for a power vent when you have a perfectly good chimney. In my experience the only reason homes are built with sidewall power venters is because it was less expensive for the builder than installing a chimney. 

They are noisy, high maintenance and prone to breaking down. I have also noticed I never find them set up correctly, usually they are setup pulling anywhere from 2-10 times as much "draft" as they should be! 

Intplm.

If you are near a area that gets a lot of snow and the power venter is lower. Snow can become an obstruction.
Always a better installation when venting to atmosphere above.

Big Ed_4

Replacing a system that has be used for thousands of years with a cheap electric fan

jesmed1

As a homeowner with two oil-fired boilers vented up a common chimney, the one improvement I'd like to make to our system is adding automatic vent dampers that will close the vent pipe to outside air when the boilers are not running.

This is because our basement gets very cold in the winter, because the barometric dampers allow cold air to draft down the chimney into the basement when the boiler isn't running. And since this is an old house, there's no finished ceiling in the basement, so the subfloor to the finished first floor living space is exposed and gets cold, making a big heat sink.

So eventually I'd like to get two of these automatic vent dampers installed to prevent that cold air infiltration. You might want to consider installing one if you do vent up the chimney. There are pros and cons. The major "con" is that if the automatic vent damper malfunctions, the burner is locked out and you don't have heat. If I get these installed, I'll probably keep a spare on hand for a quick swap-out in case one fails.

https://www.supplyhouse.com/Field-Controls-OVD-7-7-Oil-Vent-Damper-11823000-p?utm_source=google_ad&utm_medium=Shopping_ntm&utm_campaign=Shopping_NTM_New_users&gad_source=1&gclid=Cj0KCQjwwMqvBhCtARIsAIXsZpZ5NcI8CvcI4k4wZTRQhD-sBIOQ5uDfQwqutEMuK5w-LiiET6AWMO0aAgKfEALw_wcB

john123

@jesmed1: do you think there is any way of fixing the dampers in the open position so that there would not be a lock out problem if you were away for a week

OT I see you run two boilers! Cast iron? Are they in series or parallel? llh or cstee's? primary secondary or straight through? Run one to start with and bring on the second as well when it gets cold??? If you wouldn't mind sharing, I would appreciate the info.

EdTheHeaterMan

@john123 here is the info you ask for. there is a long story if you follow all the comments https://forum.heatinghelp.com/discussion/193617/weil-mclain-wgo-5-breaks-all-the-rules#latest

SuperTech

I would recommend avoiding the vent dampers. They are very problematic and prone to breaking down. A much better alternative is to install a "air boot" that makes it so the oil burner pulls its combustion supply air from outside.  Once installed there's no motors or anything else to break down in the middle of January.

EdTheHeaterMan

@jesmed1

Are you sure that the chimney is down drafting? This would be a problem, especially on each cold startup. There would be excessive fumes in the basement until the chimney heated up and the draft changed directions from downdraft to updraft.

Perhaps the flow is always up the chimney and the 100 year old construction is allowing leakage from outdoors to the basement to replace the boiler room air that is leaving up the chimney. You should double check that the cold air is actually coming down the chimney. On an oil burner Barometric draft control, a downdraft would close the damper opening while an updraft would pull the damper open.

If you do really have a downdraft when both the burners are off, then you need to look into that before it causes a problem. But from the conditions of those two boilers (from previous posts and pics) I don't think you have a downdraft problem

The dampers are still a good idea for your system, but having a spare motor actuator is all you need. Unless the actuator and the complete damper prices are not that far different.

jesmed1

@EdTheHeaterMan We don't get any fumes in the basement, so you're probably right that it's more likely an "updraft" of warm air leaving the building vs. a downdraft of cold air. I do know that whenever it's windy, the barometric dampers are flapping around when the boilers are off, so air is definitely going through the dampers in one direction or another. Probably up and out as you say.

The other piece of our puzzle is that we also have a natural draft gas hot water heater venting up the same chimney. That has no damper at all, of course, and warm air is free to draft right up the chimney 24/7. So my longer-term plan is to eventually switch over to a natural-draft direct-vent gas hot water heater located against a sidewall where it can direct-vent to the outdoors instead of up the chimney. Then at that point, we can install the automatic vent dampers on the oil boilers, and there will no longer be any free pathways for warm air to be sucked up the chimney and out of the building.

But until I can change that water heater out, there's little point in installing the automatic dampers on the boilers, because there will still be a free pathway for warm air to draft up the chimney through the water heater flue.

jesmed1

SuperTech said:

I would recommend avoiding the vent dampers. They are very problematic and prone to breaking down. A much better alternative is to install a "air boot" that makes it so the oil burner pulls its combustion supply air from outside.  Once installed there's no motors or anything else to break down in the middle of January.

@SuperTech
I have read that the automatic vent dampers can be unreliable, so I take your point. But I think we're losing so much warm air up the chimney that I feel it's worth taking the risk. I'll keep a spare unit on hand just in case.

But I don't quite follow what you said about installing an air boot for outside combustion air. The automatic damper I'm talking about isn't for the combustion air intake (which is through the burner air shutter), it would go on the flue pipe above the boiler, on the flue gas exhaust side of the boiler. So even if we had an air boot for the intake, warm air from the building can get sucked through the barometric damper and up the chimney unless there's an automatic vent damper blocking that flow path when the boiler is off.

jesmed1

john123 said:

@jesmed1: do you think there is any way of fixing the dampers in the open position so that there would not be a lock out problem if you were away for a week

@john123

The dampers in the link I posted are motor-driven and can't be manually overridden, for safety reasons. So that's the downside: they're another failure point in the system, so if the automatic vent jams or doesn't open for whatever reason, the boiler won't fire. So you have to accept that risk and have a backup plan.

john123

A tech from Field Controls told me when the power goes out, that the damper stays in its position and that spring loaded damper controls are no longer made????

jesmed1

john123 said:

A tech from Field Controls told me when the power goes out, that the damper stays in its position....

That is correct. It's driven by a servo motor, and if power goes out, the motor stops in whatever position it's in. Given that your boiler is not running most of the time, that means the most likely scenario is that if power goes off, the damper will be in the closed position, and the boiler won't run.

Of course, when power goes out, your boiler won't run anyway. So that failure scenario is somewhat irrelevant.

The more common failure mode is that the damper just sticks in the closed position despite still having power.

pedmec

How long you think the dampers is gonna last with soot forming on the blades and the side wall of the flue pipe. Unless the flue is perfectly round the damper blade always skins the inside wall of the flue pipe. thats why the damper blades are cut at the ends so it flex's

SuperTech

You want to keep the chimney warm so it can maintain a good draft. By pulling combustion air from outdoors you can negate all the negative aspects of pulling combustion air from inside the home and keep the chimney happy and drafting properly at all times.