Home too tightly sealed?

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Status
Not open for further replies.

greeby

Member
Jul 4, 2008
21
New Freedom, PA
I need some advice from the experts...sorry for the length...

Background:

I bought my current house in August of 2007.

It's a cape built in 1978, approx 1800SF between the 1st and second floors. We have a full basement (even under the garage) that's about 1100SF. Of that 1100 approx 2/3s of it are finished into office space and a living area (all open to the rest of the home). There is a laundry room with the oil furnace (door stays closed), a storage room with shelving (unheated) and a shop area under the garage that's also unheated (both also with closed doors). The windows and doors in the house were original and not very tightly sealed.

During the winter of 2007/2008 we had a fire in the fireplace on the first floor living room almost every night. Twice last year while we were burning the fireplace we smelled smoke in the house and found that the laundry room had a smoky odor (no actual smoke). The fireplace and the furnace share a chimney (split). We figured the wind was coming from just the right direction to blow smoke from the fireplace side down the flue for the furnace when it wasn't running. Since it only happened twice it was not a big issue. We keep a Nighthawk CO2 detector in the furnace room and it was reading 0 during these 2 events. As a side note..last year we kept the thermostat at or above 72 degrees during the day and evening hours (when the fireplace would be burning) and about 66 degrees at night (no fire in the fireplace).

As a side note....We had our furnace serviced in September 2007 and got a clean bill of health with the exception of a great deal of soot build-up in the furnace. The service guy said to not worry about it since we were new owners we had no idea of past service history and it may have been a while between cleanings. We agreed that if it exhibited the same symptoms during the 2008 cleaning we would address the issue.

Fast forward to the Sumer of 2008. With oil prices rising we looked around for a new source of supplemental heat for the basement living area. We purchased a pellet stove and it was installed in September. Also in August we purchased and installed all new triple pane windows and doors for the house to try and save a bit on our energy bills.

We also had our yearly furnace service in August. Again the same service guy said there was a ton of soot in the furnace and he recommended installing a fresh air vent for the furnace to increase the air to the burn chamber. We had the fresh air vent installed.

About 2 weeks later we had our first fire in the fireplace on the 1st floor. About an hour into the burn we started to smell smoke again. When we went down to the basement to the furnace room and opened the door it looked like a scene from Backdraft. Smoke filled the room and the CO detector was reading 75. I honestly thought the house was on fire. We opened the window to vent the smoke and killed the fire in the fireplace. Once the fire in the fireplace was out the smoke in the basement stopped.

The next day we did a little experiment and made a very smokey paper fire in the fireplace and went down to the furnace room to monitor and see where the smoke was coming from. Sure enough it was coming out of the flue right into the furnace room. Smoke was pouring in.

It appears that the addition of the doors and windows, coupled with the addition of the fresh air vent for the furnace, has created a problem for me. We have also reduced the temp on the thermostat to 64 in the daytime and 66 in the evening so the furnace...even on very cold days is running only about 2 hours a day. We are using the pellet stove and spending all our time in the basement where it's a comfy 76 degrees.

Now that the house is sealed very tightly it appears that the flue has turned into a fresh air source for the house? Cold air is rushing down the flue and exhausting through the fresh air vent for the furnace since the furnace is running so sparingly and not keeping the flue warm enough to prevent it? I say this because the furnace room was the warmest room in the house last year and since the install of the fresh air vent it’s now pretty chilly.

We called our chimney sweep for help and he suggested the same thing that we had thought…the house was too tightly sealed. He said that there may also be a break or crack between the fireplace side of the chimney and the furnace side of the chimney allowing smoke through. He said he’s be glad to come out and run both sides with a camera to check it out but that it would be pretty expensive to do that. He said if it’s not a crack we’re most likely screwed and won’t be able to use the fireplace.

Before I go down that road I thought I’d post here and see if anyone had any ideas on how I could solve this. The perfect solution would be some sort of exhaust fan built into the flue pipe that would keep positive pressure so smoke would not enter the flue pipe but I don’t know if such a thing exists or is even possible.

Thanks for taking an hour to read all this :)
 
exhausto or tjernlund may make a product for you.i am not sure. you may want to contact one of them and talk to one of their engineers. you may be able to extend one of the flues (wood) higher to alleviate this as well. take a look at Tjernlund.com
 
Could be negative pressure in the basement. What else is running down there? Dryer, gas hw heater, bath fan, pellet stove? Are the flue pipes terminated at an equal length at the top of the chimney? That is, are they all the same height?
 
Before I went through the expense of have the chimney sweep run a camera through the chimney I'd try opening the window that is closest to the chimney a crack and see if that helps.That should tell you if the house is to tight,if it is,the cheapest way to fix that is either leave the window cracked open or run an outside air vent.
 
I had a similar problem in my house, one chimney with two side by side flues. Build a fire in one and smoke spilled down the other. I solved this by extending my most used flue about 18" with one of Craigs (webmaster) extedaflue's. This helped most of the time but still had an occassional smoke spillage so I installed outside combustion air to both and that completely eliminated the problem.
 
That's what I'm thinking here Todd. Greeby may need an extendaflue.
 
BeGreen said:
Could be negative pressure in the basement. What else is running down there? Dryer, gas hw heater, bath fan, pellet stove? Are the flue pipes terminated at an equal length at the top of the chimney? That is, are they all the same height?

Water heater is electric and the dryer (in the same room) wasn't running when we had the problem.

Pellet stove has an OAK, but it wasn't running when the room filled with smoke either.

Both flues are terminated at the same height at the top of the chimney.
 
BeGreen said:
That's what I'm thinking here Todd. Greeby may need an extendaflue.

The extendaflue looks like exactly what I need.

I don't know my flue size...I guess I'll call my sweep and see if he knows the size.
 
greeby said:
...About 2 weeks later we had our first fire in the fireplace on the 1st floor. About an hour into the burn we started to smell smoke again. When we went down to the basement to the furnace room and opened the door it looked like a scene from Backdraft. Smoke filled the room and the CO detector was reading 75. I honestly thought the house was on fire. We opened the window to vent the smoke and killed the fire in the fireplace. Once the fire in the fireplace was out the smoke in the basement stopped.

The next day we did a little experiment and made a very smokey paper fire in the fireplace and went down to the furnace room to monitor and see where the smoke was coming from. Sure enough it was coming out of the flue right into the furnace room. Smoke was pouring in.

It appears that the addition of the doors and windows, coupled with the addition of the fresh air vent for the furnace, has created a problem for me. We have also reduced the temp on the thermostat to 64 in the daytime and 66 in the evening so the furnace...even on very cold days is running only about 2 hours a day. We are using the pellet stove and spending all our time in the basement where it's a comfy 76 degrees.

Now that the house is sealed very tightly it appears that the flue has turned into a fresh air source for the house? Cold air is rushing down the flue and exhausting through the fresh air vent for the furnace since the furnace is running so sparingly and not keeping the flue warm enough to prevent it? I say this because the furnace room was the warmest room in the house last year and since the install of the fresh air vent it’s now pretty chilly.....

It sound to me that the addition of the fresh air vent to your furnace room (confirm it is an open vent to the room, not directly connected to the furnce), has allowed the furnace flue to reverse, and now it is pulling smoke down the furnace flue. Adding the other air seal issues has magnified the problem for sure.

Two things to consider - the flow reversal, and the reason for the smokey flue gasses.

An extend a flue is going to help keep the smoke out of the house, but it isn't going to keep the cold air that is running down the reversed furnace flue out of the house. All the extend does is allow for the smoke to be more diluted before the air gets sucked into the adjacent flue - that is a good thing, but it would be better to not suck the air into the house in the first place.

To help the reversed flue - if you could provide for heated makeup air to the furnace room, then the flue would continue to draft when the furnace was off. Anything you can do to keep the furnace flue warm will help. As well, if you can change the air vent to a directly connected outdoor air supply, aka an Outside Air Kit to wood heat folks, or OAK, (that will depend on the furnace design), you will help in 2 ways:

First, you will avoid the smoke drawn down the flue from entering the house, as any air entering the house will vent outside.

Second - An OAK will help avoid the reversed flow by isolating the furnace and its flue from the effects of the relative negative pressure from the basement location of the furnace. It is this negative pressure, coupled with the cold furnace flue, that is likely causing the reversal to begin with - especially since you say that the problem got worse when the vent was installed.

The vent is sucking cold air into the furnace room, which cools the flue faster, and then reverses it. Because the entire basement has a relative negative pressure to outside, the reversal continues as the vent can't supply all the air demanded by the pressure issue.

Give this link a read "Keeping the heat in" - http://oee.nrcan.gc.ca/keep_heat_in/index.cfm , especially the chapter on air leakage control. It will give you some good background that you can apply as you watch the problem, and help you understand how other issues you have "Fixed" may be contributing to the problem.
 
Question - Edit - by fireplace, do you mean an open hearth fireplace? if so, that is the main source of the air loss that your cold flue is trying to make up. Installing an insert stove, which will vent way less air, will likely help a lot with the air exchange issue that the cold flue and basement vent are trying to provide for.
 
[quote author="oconnor" date="1229369757
It sound to me that the addition of the fresh air vent to your furnace room (confirm it is an open vent to the room, not directly connected to the furnce), has allowed the furnace flue to reverse, and now it is pulling smoke down the furnace flue. Adding the other air seal issues has magnified the problem for sure.

[/quote]

The OAK is attached directly to the furnace.

1.jpg

2.jpg

3.jpg

4.jpg
 
oconnor said:
So there is enough of a negative pressure in the basement to draw from both the flue and the vent.

Do you have an open hearth fireplace?

If so, that will be a major source of air leaving the house, in comparison to a wood stove or insert stove.

Yes, it's an open hearth fireplace with the requisite doors. We usually burn with the doors open.

So if I open a window in the room with the fireplace I may see an improvement?
 
I think so - you will be giving the hearth an alternate source of combustion air, so it will draw air into the house thru the window instead of thru the furnace flue.

Still, you aren't actually heating your house if you do that, you are just watching flames and making smoke (dirty, unburnt smoke at that, when compared to an EPA appliance). An open fireplace, doors or not, is at best 10 percent efficient, and as poor as actually being negative efficient, in that it draws so much air into the house from outside that it has a net cooling effect on the house as a whole.
 
Status
Not open for further replies.