Furnace flue cold air draft issue/question

[Roxburyeric]

History: First year burning wood - Jotul 550 insert. I have a 2,500 sq. ft. house open floor plan and open to 2nd floor and with a full finished basement (additional 1,000 sq ft) (built 1999 pretty tight construction but not super tight) 25 ft. chimney on the outside of the house, 6 inch SS liner with top and bottom plates (not insulated). I leave the hot air oil fired furnace on 62 and it will come on occasionally when the temps are in the 20's or below. Insert is on the first floor not in the basement. Basement is pretty cold.

Issues: Sometimes I hear the furnace cycle on and then off in less than a minute, which I never heard it do in prior years, when heating only with oil. Also, I have noticed that there is cold air coming down the furnace flue (stick my hand through the damper swingy thing (technical word there). Is this cold air a problem and could it be the cause of the furnace kicking on for short bursts? Also when the furnace does come on how can it change the draft that quickly. I do have a CO detector 6 ft. away and no issues.

Thoughts and help appreciated.

 

[begreen]

Where is the thermostat for the furnace located in relation to the woodstove? It could be that its differential or "swing" is set too narrow or sensitive. It probably should be set to a 1.5 or even 2 degree swing to avoid short cycling the furnace.

 

[Roxburyeric]

It is in the dining room away from the fire and tends to read in the 60's while the family room where the fire is is in the 70's. Problem is the family room is two stories and open to the 2nd floor hall way and bedrooms so most of the heat goes up and the ceiling fan needs to be set on 3rd fastest setting to bring the heat back down (a little bit). I will check the setting, but I think it has always been set as you suggested and maybe it got bumped.

 

[begreen]

Usually the swing setting is not easily changeable. Is this a digital or analog thermostat? What make/model?

If you can post a diagram of the house floorplans for the 1st and second floor, perhaps there is a way we can suggest to even out the heat.

 

[Henz]

tht is exactly what I did with my Digitat/Programmable thermostat....I set the swing to 2

 

[oconnor]

Sometimes an oil furnance will sound like it is cycling, but what can be happening is that it isn't lighting off, and it will shut down. They have a sensor to ensure that they are getting full flame, and if they don't get that condition within a given period of time, they will shut down to avoid a problem that would involve too much fuel when they ignite. If the flue isn't drafting or is reversed flow, then it may not actually be igniting the oil. You may want to get it looked at.

 

[Roxburyeric]

I have a manual Honeywell T87F thermostat. Looking at an online install guide it really doesn't give you the option to set the swing setting, just a setting based on the zone system I have. Which is first floor is the main zone controlled by this thermostat (set heat/cool and fan on or on auto fan) and a 2nd floor zone that i can only set the temp on. I tried getting a digital one - but they do not sell ones that work for this set up at Home Depot/Lowes, etc. - They only have them through the HVAC contractors since it needs to be set up for the type of zone system you have.

What oconnor said is what I was fearing or thinking might be happening. I guess i should have it checked out. Thanks

 

[LLigetfa]

My guess is the furnace has enough safety smarts on it to detect that the draft is bad and shuts down as a safety feature.

 

[PeteD]

At the risk of stating the obvious, turn the thermostat up 5 or 10 degrees above ambient and let the heat come on. If it doesn't stay on, you have a problem.

Pete

 

[LLigetfa]

My gas furnace had a bad sensor and about a third of the time, it would abort the cycle. A new sensor cured it.

If the problem is a reversing flue from a lack of makeup air, you may have to provide more makeup air or a dedicated OAK for the Jotul. You might also want to check for air loss from stack effect or clogged HRV screens, etc.

 

[North of 60]

My guess is the furnace has enough safety smarts on it to detect that the draft is bad and shuts down as a safety feature.

Its an oil furnace. This will make it a forced draft. The burner safety control module would lock out and would have to be manualy reset each time. NG and LP burner flame safeguard controls will re-try. Not oil burners. He hasn't mentioned about resetting anything as it has been cycling. A high temp limit could be causing this in the heat exchanger if not enough air is being moved. PeteD has a good suggestion. Is the burner coming on and not the blower before it cycles off? Will check in tommorow eve.
The cold air being mentioned has no relation to be calling for the burner to come on. Sounds like you do have a negative in the house though.

 

[Roxburyeric]

I'll try to cover most suggestions: I have turned up the heat causing it to come on and heat up the house. Even without turning it up it does come on and produce heat, with the blower coming on also. So most of the time it works fine. It is just every once in a while I hear it cycle on and then shut down within a minute or less. I have also noticed that some times the draft (cold air) in the furnace flue is stronger than other times (again placing my hand in the flue damper next to the furnace - when it is off and not hot). I have not had to reset anything to keep the furnace working. The Jotul 550 insert does not have an option or area to add an OAK. I have been thinking it could be a nagetive draft due to the lack of makeup air in the house. I have also noticed a rateling (sp.?) sound just above the furnace burn area when the fan is on. Maybe something is loose with the fan and is causing the air to not move enough - although it feels normal when checking the airflow at the grates in the house. I'm going to call an HVAC guy I know today and pick his brain. Thanks again

 

[begreen]

If you pop the cover off of the T87, towards the bottom, you should see a small copper "wiper" adjustment blade with tiny numbers on it. That is the heat anticipator setting. It depends on the furnace, but generally, a lower setting of say .4 will give a narrow swing range of say ~1 degree. A setting of .6 might give a swing range of ~2 degrees.

If negative pressure is the issue, consider an outside air kit for the furnace.

 

[Roxburyeric]

I ended up speaking with my Oil Company and they told me that the down draft of cold air is normal (possibly a negative drafting issue) and that the furnace will automatically correct the draft with a fan and the heat coming on. If it couldn't correct the draft then the safety features would shut down the system and I would have to reset the furnace before it could come on again. I have not had to reset the furnace at all. They said the quick cycle is probably due to the woodstove heat and drafting within the house from the ceiling fan moving air around and the cold air return vents sucking in air close by (essentially the thermostat getting a warm air blast that would tell it the room is hot enough already and cycle off quickly. They also said a drafting issue in the flue would cause an oil smell to be present or the CO detector I have close by to go off (which I have not had). Basically I think I have been a little paranoid as this is my first year burning wood and I am noticing every little change.

BeGreen - in reading the manual it looks like it has to be at one particular setting based on the zone system I have, so I don't think I can change it without it effecting the zones. Of course I don't know much about it. I really would like a digital programmable thermostat but being frugal I don't really want to spend several hundred dollars for a unit with professional installation.

Thanks to all

 

[PeteD]

Thermostats are not that that expensive for a simple digital residential heat/cool model that is programmable. Also, they are very easy to install. They are great first step to saving energy and ensuring home comfort.

Look into getting one and installing yourself - you can do it.

Pete

 

[Roxburyeric]

Pete - I did look into it but based on my two zone system with the upstairs zone tied through the first floor zone I need a special unit that is not sold at HD and/or lowes but only through an HVAC Company because knowledge of the zone programing is needed (at least that is what I have been told). So the cost of the unit is well over $100 and most hvac Companies would want to install it.

 

[North of 60]

Pete - I did look into it but based on my two zone system with the upstairs zone tied through the first floor zone I need a special unit that is not sold at HD and/or lowes but only through an HVAC Company because knowledge of the zone programing is needed (at least that is what I have been told). So the cost of the unit is well over $100 and most hvac Companies would want to install it.

Somone is feeding you a line. Your existing stat is a basic Single stage heat/cool stat. Thats as basic as they come. Three wires unless you are using the fan option which makes four. If you are only using it for heating then only two wires are needed. To have two true zones you will have two stats.
Any basic digital programmable T-stat can do more than a basic T87F.

 

[begreen]

I ended up speaking with my Oil Company and they told me that the down draft of cold air is normal (possibly a negative drafting issue) and that the furnace will automatically correct the draft with a fan and the heat coming on. If it couldn't correct the draft then the safety features would shut down the system and I would have to reset the furnace before it could come on again. I have not had to reset the furnace at all. They said the quick cycle is probably due to the woodstove heat and drafting within the house from the ceiling fan moving air around and the cold air return vents sucking in air close by (essentially the thermostat getting a warm air blast that would tell it the room is hot enough already and cycle off quickly. They also said a drafting issue in the flue would cause an oil smell to be present or the CO detector I have close by to go off (which I have not had). Basically I think I have been a little paranoid as this is my first year burning wood and I am noticing every little change.

BeGreen - in reading the manual it looks like it has to be at one particular setting based on the zone system I have, so I don't think I can change it without it effecting the zones. Of course I don't know much about it. I really would like a digital programmable thermostat but being frugal I don't really want to spend several hundred dollars for a unit with professional installation.

Thanks to all

The issue would be the same with a digital thermostat. They also have a heat anticipator (swing) setting. Be brave, pop the cover of the thermostat, record the current heat anticipator setting, then bump it up a bit. I'm guessing that the installer didn't do the amperage calcs for the zone valve and it just needs to be set a bit higher.

BTW, I put in LUX digital thermostats on our system (before the current heat pump) for a grand total of about $29 at Home Depot. Most likely this is a simple 2 wire system on the zone valve and fairly easy to replace.

 

[Roxburyeric]

North and Begreen: Thanks - I consider myself pretty handy so I will be looking to replace the Thermostat myself again. Again, I have a manual Honeywell T87F thermostat for my first floor main zone (I can set heat/cool/off and fan on or on auto fan) and I have a 2nd floor zone with a manual thermostat that I can only set the temp on. I want to replace the first floor thermostat. Any advice on what to get?

 

[chad3]

Mine does the same thing, however, I'm guessing that mine is based on the hot water also running through the system. Is yours a stand alone or do you have hot water in the same burner? The short cycles are getting water up to temp and then shutting down (at least in my system)
Just a thought.

 

[PeteD]

Mine does the same thing, however, I'm guessing that mine is based on the hot water also running through the system. Is yours a stand alone or do you have hot water in the same burner? The short cycles are getting water up to temp and then shutting down (at least in my system)
Just a thought.

I have have tankless oil with FHW, so I had the same thought. But he has air I believe, because he said furnace.

 

[PeteD]

Deleted double post.

 

[LLigetfa]

...I leave the hot air oil fired furnace on 62...

That pretty much removes all doubt.

 

[begreen]

North and Begreen: Thanks - I consider myself pretty handy so I will be looking to replace the Thermostat myself again. Again, I have a manual Honeywell T87F thermostat for my first floor main zone (I can set heat/cool/off and fan on or on auto fan) and I have a 2nd floor zone with a manual thermostat that I can only set the temp on. I want to replace the first floor thermostat. Any advice on what to get?

I like the basic LUX digital thermostats. However, you'll need to know how the zone valve is wired to the thermostat first. If 2 wire, the basic TX500 will work. If it's a 3 wire zone valve then you'll need the TX9100E model. Honeywell has come out with a digital consumer line. I haven't used any of them, but they might work out ok with the same caveat for the 2 wire vs 3 wire zone valve wiring.

 

[Roxburyeric]

Hot Air system: BeGreen - I'll check the Thermostat when I get home from work later. Thanks

Eric