Overcoming Negative Pressure in Basement

[jeffs]

I discovered early on that we have some issues with negative pressure. Our woodstove is in a large, finished room in our basement. In an adjacent room (shop and utility area) is our forced-air oil furnace, which exhausts to the outside via a power vent (vents to about 16" above ground level). There is a door between these rooms. To start our woodstove, I have to make sure the furnace is not running, and open a window until I get a good fire (draft) going. Have been doing this for several years now, and have it down to a science, so that if I follow these steps, I rarely have a start-up issue. The chimney for the stove extends the full height of our 2 story house, plus another 4' or so, and has an insulated SS liner. We have the stove and chimney cleaned regularly. We have the furnace and vent cleaned regularly.

This winter, following a couple of really cold nights, we had heavy frost on the stove pipe inside the basement. This was on nights we were NOT using the woodstove. In talking with a friend who is a home builder, he suspected that our furnace/power vent is creating enough neg pressure in the basement to pull air down the chimney, and created the frost issue. Why this never happened before I can't explain?

More recently, we had the CO detector going off on the second floor. This was 2-3 days after we had used the woodstove and had let the fire go out. Our CO detector gives a digital readout, and I traced the issue to the basement room where our woodstove is located. Investigating the stove, I found there were still a lot of hot coals/embers under the ashes. It seems they were smoldering but not making enough heat to create a draft strong enough to counter the neg pressure. The CO issue has never happened before. Only once did we get a smoky backpuff a day after burning, that was several years ago and I attributed it to the weather. It hadn't happened since.

Our contractor friend has suggested a fresh air kit for the furnace, so that it draws most air it needs from outside, thinking this would eliminate the negative pressure. Our furnace service tech says we should avoid that as it may violate our oil price/service contract. He suggested an OAK for the woodstove. So my big question is, would an OAK for the stove be enough to eliminate the negative pressure being created by the furnace and power vent in the next room?

 

[bholler]

I would supply air to both. That may fix it but you may also have a general low pressure in you basement as well sometimes and oak can over come that some times it is not enough. I would absolutly install an oak on the wood stove and i think it is a good idea for the furnace as well. I see not reason that would effect your service contract as long as it is the right supply and is installed correctly

 

[mstoelton]

Why does your furnace need a power vent to the outside? It seems like this is a way for the oil company to ensure you need to buy more oil in order to heat the air that is being exhausted. I agree with bholler oak to both and quit using the powervent.

 

[bholler]

Why does your furnace need a power vent to the outside? It seems like this is a way for the oil company to ensure you need to buy more oil in order to heat the air that is being exhausted. I agree with bholler oak to both and quit using the powervent

They need a power vent because it is not vented into a chimney i assume

 

[Chimney Smoke]

They need a power vent because it is not vented into a chimney i assume

Why does your furnace need a power vent to the outside? It seems like this is a way for the oil company to ensure you need to buy more oil in order to heat the air that is being exhausted. I agree with bholler oak to both and quit using the powervent.

Powervents don't require you to burn more oil. It's an electric vent to send the furnace exhaust outside without using a chimney flue.

Location must play a big part in basement negative pressure situations. I have a woodstove in my basement next to the oil burner and dryer. My chimney goes straight up through the two story cape. Even when the stove is cold I can feel a solid draft when I open the stove door. I've started fires with both the furnace and dryer running and also never had a draft issue. Very strange some experience the opposite.

 

[bholler]

Location must play a big part in basement negative pressure situations. I have a woodstove in my basement next to the oil burner and dryer. My chimney goes straight up through the two story cape. Even when the stove is cold I can feel a solid draft when I open the stove door. I've started fires with both the furnace and dryer running and also never had a draft issue. Very strange some experience the opposite.

There are very many variables that can cause a negative pressure problem if the house is to tight it can happen but if the stove is in the basement and the house is leaky you can also get negative pressures from the chimney effect in the house If air is leaking out the upper floors faster than it can come in the basement you get negative pressure lower in the house. Generally furnaces alone generally don't consume enough air to cause a problem there has to be something else going on. And yes you are totally correct about the power vent. And a power vented furnace will not consume any more oil or air for that matter than one vented into a chimney.

 

[Don2222]

Hello
My boiler has a regular chimney but made my wood stove back draft when it fired so I put in the boiler outside air and it helped a lot.
It was easy to install right next to the central vac. That creates a little neg pressure upstairs! LOL

 

[bholler]

My boiler has a regular chimney but made my wood stove back draft when it fired so I put in the boiler outside air and it helped a lot.

Yeah the furnace absolutly can be the thing that puts it over the edge as your instance shows so to the op i would put a fresh air intake on both it may very well fix the problem. But you may also have more going on

 

[begreen]

I'm agree with bholler, supply outside air to both the stove and oil burner. I don't see where or how this would negatively affect the oil burner. Tell the current oil co. that this might be the end of their service contract if you have other companies in the area that can do the same job.

 

[otsegony]

I had a similar negative pressure problem with my house constructed in 2004 with an oil boiler equipped with a power vent. We were getting smells throughout the house, popping sounds whenever we opened doors or windows and other issues. The power vent seemed to be the source of most of the problems. We equipped the boiler with a factory outdoor air kit and it greatly reduced the problems. Interestingly the problem has gone away almost entirely since we started burning wood full time and only use the oil boiler as a supplemental system. I'm not sure why the oil company said that the outdoor air kit would void the service contract since they are a common option from the manufacturer and don't seem to impact the operation of the boiler in any negative way.
The other solution we looked into at the time was a heat recovery ventilation system. These systems preheat outside air coming into your home and can greatly reduce negative pressure. Luckily we didn't need it in the end as they were kind of pricey.

 

[HotCoals]

OAK might not work in the basement for the stove.
Intake should be lower then the stove I hear.

 

[jeffs]

Thanks for all the responses guys!

Our service and price contract with oil company is conditional on not having any other major heat source in the house. (Oil company wants a monopoly I guess.) We are in a rural area and do not have a lot of options on oil service, and they are the best price, best qualified, so we really don't want to lose them. The service tech, who we know/trust enough to talk to about this, advised against an air kit on the furnace, not because it would be be detrimental to the furnace, but he thinks it will be a tip-off to the oil company that we're having issues, and lead them to investigate why...

Having said that, if we felt enough people with expertise in this subject were positive that we really need an air supply to the furnace, and were 95% sure this would solve the issue, I could probably have someone else install it. I can install the one for the woodstove, I'm pretty versed in home remodeling/repair.

Some more info:

We only burn the woodstove Friday thru Sunday. Use the furnace the rest of the time. Woodstove is Napoleon 1900 (don't ask).

House is very tight. Built in 1997, well insulated, vapor-barrier plastic in walls, good quality windows/doors, etc.

Bholler– A power-vented furnace doesn't consume more air than a standard chimney? I assumed it did, but I'm not an expert. The PV comes on and runs for a few minutes before the furnace fires, runs while the furnace runs, and runs for 5 minutes after the furnace shuts off. This is correct operation. Seems like that thing really sucks a lot of air. There is also a barometric draft reg between furnace and power vent. When the whole thing is running, that is open about 35 degrees from close.

What else causes neg pressure? House is 2 stories, med/large colonial. Built on a slope, so one side is about 2-1/2 stories (about 3-4' of basement is above grade on that end). The tall end is where the chimney is. I cut 2 registers in the floor between basement and first floor to let heat up from basement when stove is burning. Have a fireplace on first floor which we never use, and have closed-up tight. We have exhaust fans in 2 upstairs bathrooms which run as needed. Have a range hood fan we use as needed (on first floor). Dryer (on first floor) runs as needed.

 

[bholler]

Bholler– A power-vented furnace doesn't consume more air than a standard chimney? I assumed it did, but I'm not an expert. The PV comes on and runs for a few minutes before the furnace fires, runs while the furnace runs, and runs for 5 minutes after the furnace shuts off. This is correct operation. Seems like that thing really sucks a lot of air. There is also a barometric draft reg between furnace and power vent. When the whole thing is running, that is open about 35 degrees from close.

a natural draft furnace would be sucking air the whole time whether it was running or not unless it is a high effincy one with a auto damper that closes when it is not running. The power venter should be calibrated so it provides the same draft that the chimney would naturally when the furnace is running how long does it run before the furnace kicks on? it should not be very long at all.

What else causes neg pressure? House is 2 stories, med/large colonial. Built on a slope, so one side is about 2-1/2 stories (about 3-4' of basement is above grade on that end). The tall end is where the chimney is. I cut 2 registers in the floor between basement and first floor to let heat up from basement when stove is burning. Have a fireplace on first floor which we never use, and have closed-up tight. We have exhaust fans in 2 upstairs bathrooms which run as needed. Have a range hood fan we use as needed (on first floor). Dryer (on first floor) runs as needed.

A tight house will not be as prone to negative pressure from stack or chimney effect but it can still happen and the vents in the floor make it worse. the bathroom fans the dryer and the kitchen fan can all contribute as well as the hvac if it is not balanced. And the fireplace if it is not really sealed can be a big factor as well

 

[velvetfoot]

My colonial style house is only about 9 years old, pretty tight, and I get negative draft in the basement, as well as the first floor. It's overcome easy enough, but I have no idea why, except for maybe 'chimney effect'.

 

[bholler]

A leaky attic door or hatch can be a big cause

 

[begreen]

That CO reading was a red flag. It sounds like the basement needs makeup air. If the oil company has you by the nuts contract , install an ERV or HRV there or consider installing an insert upstairs in the fireplace and not burning in the basement.

 

[fire_man]

A tight house will not be as prone to negative pressure from stack or chimney effect but it can still happen and the vents in the floor make it worse. the bathroom fans the dryer and the kitchen fan can all contribute as well as the hvac if it is not balanced. And the fireplace if it is not really sealed can be a big factor as well

bholler: Interesting point - are you talking about forced hot air feed vents? Why would these make a difference? And what if a return vent is located in the same room as the stove?

 

[bholler]

bholler: Interesting point - are you talking about forced hot air feed vents? Why would these make a difference? And what if a return vent is located in the same room as the stove?

No in that case i am referring to the vents that the op cut in the floor between the basement and the first floor which allows allot of air to rise and if there is a tendency in the house towards a stack effect then those vents can make it worse. The hvac system can cause problems if the stove is to close to a return or the system is unbalanced.

 

[jeffs]

The fireplace on the first floor is a pre-fab unit with very small firebox, we could not find an insert that would fit in it and give us decent burn-times. Plus, we spent several thousand on the stove we put in the basement, plus ss insulated liner for chimney, so don't want to abandon that.

Registers were cut in floor to allow heat from basement to rise. Because this is a finsihed basement, there is a drywall ceiling there, and a lot of heat was getting trapped in the basement. We put a fan at the top of the basement steps, and floor registers to allow hot air to rise into the family room and living room upstairs.

The fireplace is sealed very, very tight, as it would be ice cold/drafty in the winter, from air coming down the chimney. So we have it blocked off with Rmax behind a plywood cover and foam weather-stripping.

Only attic door is in a closet, usually closed, and no gaps around the panel. Really the only openings to outside are the exhaust fans in bath, kitchen, and dryer. And these are not used excessively.

How do I know if the HVAC is balanced? the tech was out on Monday and checked furnace and PV. He even talked to the people at Field Controls to calibrate the PV to their exact specs. (It wasn't off by more than a hair.)
HVAC is central-heat/air, and there are no returns in the basement. Returns are placed in each room on first and second floors (vs. one big return).

 

[bholler]

I would hook up the intake on both units and see if that fixes it both are simple cheap things to try. If that doesn't work i would recommend getting a sweep out and possibly a different furnace guy. In my experience the techs from the oil companies are far from the best furnace techs around.

 

[Nelson]

I don't know why adding an OAK to your furnace would void any type of contract. As I understand it, it would be code now to draw fresh outside air for any new furnace. Why would it matter if you installed one for your existing? Contract or not, I would want my furnace drawing air from the outside. My guess is that would put a huge dent in your neg pressure issue.