Fresh makeup air

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Old 11-28-12, 06:52 AM
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Fresh makeup air

Hi, my gas boiler has worked fine until I installed a wood pellet stove with it's own makeup air supply connected directly to it, we leave the door at the top of the stairs opened so the heat will rise,the problem is spuratic but on occasion the boiler shuts down on Hi flue temp safety,would adding a fresh air supply from outside solve the problem?This house is very tight,I would install a damper in the duct so it would only open when the boiler was calling.

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  #2  
Old 11-28-12, 09:03 AM
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Hi Geo,
The issue is more involved than your furnace shutting down. With a very tight house, adding a combustion appliance can be a problem. You have gone with a makeup air supply for the pellet stove, but is it working? Depressurization of a tight house doesn't take a lot as dryers, bath fans, and kitchen fans can all combine to exhaust more than the house provides.

Have you had the house tested?

Bud
 
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Old 11-28-12, 10:30 AM
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Fresh air makeup

Not quite sure how to test the house.I am familiar with commercial boilers and the makeup air supply is interlocked so that the boilers won't start if there is no makeup air supply.
 
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Old 11-28-12, 11:31 AM
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Hopefully some of the heating guys will jump in on the high temp switch and if/how the new stove might be involved. Generally, when you have a natural draft appliance, not sealed, then as you tighten up the house you want to know how tigh it is. An energy auditor would run a blower door test to determine how tight and then a "CAZ" worst case combustion air zone test to be sure there is sufficient incoming air when everything that exhausts is running.

From the sound of your problem, and I'm not a HVAC guy, you might have been borderline before the install and now running short on make up air. But it could be something entirely different. Let's see what the pros say.

Bud
 
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Old 11-28-12, 07:46 PM
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Well, what high limit is tripping ?
Is it the one on the draft hood ?
this can be caused by,
blocked vent (the actual name of the limit control), ie chimney is getting clogged
Can also be caused by a back drafting chimney.

Is it the device by the burner tray ?
This can be caused by,
flame roll out (again the name of the device), ie the boiler HE is clogged to the point where the flames can no longer go thru the heat exchanger.
Believe it or not, I have seen this too many time. We fixed a slant fin boiler that had been run thru a basement reno. the only reason the house didn't birn to the ground was because the flames melted the 120vac wires inside the armoured cable thus shorting the supply out. And yes the owners of the house where home.
Typically a back draft or inadequate combustion air does not trip this often.

If your chimney is back drafting, you need professional help. Make up may not be the fix, only a bandaid. Poorly cleaned boilers, and dirty chimneys will kill.

If you are simply lacking combustion air you can bring in outside air and duct it down to the floor, even put 2 90 elbows on it to form a u as a heat trap.

I suspect that if this problem just started after installed the pellet stove, then you have some pretty serious issues.
 
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Old 11-29-12, 06:15 AM
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The limit switch in the draft hood is the culpert,problem started after the pellet stove was installed and seemed to clear up after I connected the makeup directly to the stove which I am going to check an make sure it is not blocked and the combustion blower is working.The boiler issue is sparatic and will clear-up when I open a basement window a bit.If I bring in outside air what size pipe would you suggest ?
 
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Old 11-29-12, 06:41 AM
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Your input plus TOHeating's is definitely point towards the house being very tight. That being the case, your decision on make up air should be based upon the worst case. Relying of opening a window is a poor patch, especially if CO is at all a possibility. Other air quality issues are, moisture, Radon, mold, and other indoor pollutants and all need to be properly vented, it is a health and safety issue.

Some of the issue can be handles with an air exchange unit, the rest could be a make up supply as you are discussing. But without the numbers from testing, I can't say what would be a minimum.

Sorry, I wish I had more to offer, but with my limited HVAC knowledge and no onsite information the ball is in your court and the picture may not be as bad as I'm painting. It is just that you need to know what might be happening.

Bud
 
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Old 11-29-12, 01:53 PM
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make up air size depends on how many BTU the appliance is.

Do you have wood burning fireplaces ?
A large volume kitchen exhaust fan ?
 
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Old 11-29-12, 05:23 PM
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Wood pellet stove with is on piped in makeup air,today I started the 3 exhaust fans and had the pellet stove going and boiler worked fine, it is very spasmodic and hard to pin point , it has run fine all day.
 
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Old 11-30-12, 06:01 AM
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Where are the two heating units vented? How much chimney is exposed to cold air?

TO is correct, make up air for the boiler is based upon the size of the unit. But make up air for the house is based upon how tight the house is. One or both may improve the situation, but I'm trying to get you above the indoor air quality/safety requirements for a home. There may or may not be an issue, but until you have it tested you are still on the borderline and really don't know what safety margin you have.

Tight homes can be a disaster. They can degrade slowly with moisture problems occurring where you can't see or worse CO/health issues that catch you off guard. If you know the house is tight and your symptoms do support that, you owe it to your family to have it tested.

Bud
 
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Old 11-30-12, 06:37 AM
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I am not quite sure who would do the necessary testing,would an energy survey do the job?
 
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Old 11-30-12, 08:37 AM
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There are low cost (sales gimmick) type energy audits that aren't really audits. That's why they call them "surveys". You may not need a full audit, so talk to the energy auditor and ask for a blower door test and a "BPI" certified CAZ (combustion air zone) test.

If you can find an energy auditor that is independent of the contracting side, then you may avoid a sales approach. The two solutions on the table would be a "HRV" or "ERV", similar in function in that they exchange inside air with a like quantity of outside air and recover some of the energy that would normally be lost. An ERV recovers moisture as well. Or a make-up air system that could be a simple open duct or more complex damper that opens only when needed. Maybe an outside air kit for the burner.

I have limiter experience with pellet stoves, but my understanding is that they require much less combustion air than a fireplace. You might check the manual to see if they state the volume of required combustion air. If it is low, that tells you how close to borderline your house is, as the problem arrived with the stove and diminished when the outside air supply was added.

There are other indicators of a tight home. High humidity, moisture on the windows, musty smell (especially in the basement), and even a noticeable suction when opening and closing doors. Typically, a tight home would have had to be built that way, I mean a significant effort on sealing and that was rare just 10 years ago. So age of house is an indicator of sorts.

Pick up a couple of CO detectors and a couple of dual function smoke detectors if none, and welcome to the world of wood heat. You might also look into a back-up power source for the stove to be able to run it when the power is out.

Bud
 
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Old 12-01-12, 04:33 PM
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Good info, the house was built in 2007 a modular home ,has the CO/Smoke detectors,I am looking into the blower door test, I am planning on installing a makeup air duct with motorized damper any way, I have installed a temp 6" round duct through a cellar window as a test and haven't had any issues as of yet.I do believe the house is boardline but will wait and see how the test turns out.
 
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Old 12-02-12, 06:00 AM
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Save your money right now on the blower door test. Option that later. Most pellet stoves I have seen are direct vent which mean they supply their own combustion air through concentric venting.
Wait and see if the combustion air pipe solves the problem. If so install a product like a fan in a can or some other device. It sounds like the blocked vent switch is tripping which indicates one of two things. Reduced draft in the chimney due to a slight blockage or tight house so when the boiler fires the only place to get combustion air is down the chimney. The downdraft can be caused by needed air for combustion or the fans in the home. Either way you need more air if the temporary pipe you installed helps.
 
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Old 12-02-12, 06:13 AM
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Thanks, that is the approach I am taking, the pellet stove has it's on makeup air duct installed directly outside,I did find the front door on the pellet stove a bit loose so adjusted the latch to make the door tighter.
 
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