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Over the past few years, I have been making gradual but steady progress in sealing off my “leaky” ’50’s vintage house. The furnace room has never had a fresh air source for combustion, so all combustion air was drawn from the house. As the house has become progressively “tighter”, the furnace now sucks all the air from the remaining “leaks”, which results in large amounts of cold air being drawn from fewer areas, which noticeably cools those areas of the house (especially when we have a cold spell like we’ve had this week in the NE).
I just checked w/ the building dept., and they just require 4″ metal ducting, terminating 6-8″ above the floor near the furnace & water heater. I’ll bring it in at ceiling level, & turn down to the floor.
Anything I’m missing here? Simple vent to the outside w/ a screen (no damper, obviously, since it is designed to pull air in).
Thanks in advance for any pointers.
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Per
Heres a good article from a recent JLC click here
-pm
*Patrick: Thanks for the article reference (I don't check JLC as often as I could/should)Fred L(ug..): Glad you showed up on this one. As a preface, I have to say that I agree with most of your thoughts/posts, but this one has me scratching my head. Once upon a time, I spent good money on an engineering degree, so let's see if I can put it to good use.Yes, wind can cause depressurization, especially when it occurs at a constricted ingress/egress point for air to/from the house. Any depressurization (whether from a dedicated vent or house-wide) can result in a rollback of the burner flame. As a solution to the vented scenario, why not have a reverse baffle (i.e. spring loaded, opening up only on suction from the house, not negative pressure from outdoors, i.e. the reverse of a dryer vent) to prevent adverse winds from sucking out of the house)? My concern at this point is that the burner wants (NEEDS!) air when it's heating the house. There are 2 major sources of combustion air, which I haven't plugged yet because I'm not sure of the repurcusions. One is the vent opening from the range (exhaust), and the other is the dryer. When the furnace is running, it is scooping air in as fast as it can get it. Also have airflow coming from less acessible areas (crawlspaces which would make your demo in FHB of tough vapor barriers look easy!), which chillls the whole family room. To address your specific concerns, consider the following:1)W/ a reverse baffle, there is no "hole in the cellar", & it's certainly no worse than the current draw from the great outdoors (ps...ceiling plane is pretty much sealed).2)Again, w/ reverse baffle, furnace room temp. shouldn't be an issue. As it is, it overheats. 3)With doors opening constantly (schoolbuses & all) & combustion gases going up the chimney, how does this become my primary airflow? I see it as a way of short-circuiting the "suck from everywhere" situation, by providing a path of lesser resistance for the required combustion air.PS. The top is sealed, the bottom is more porous than I like, & if you know of a good cells guy in my neck of the woods (one you would recommend), let me know.Thinking, Per.
*Question/suggestion re flappers: Stick a draft guage in your flue. You should be getting .01 to .03. (too high can cause air curtain...) Now, remove guage and blow across the tip to see how much force it takes to create .01 to .03. Now blow against your flapper to see if it'll open with that much force.Perhaps (and this just an idea, I don't know enough to make it a suggestion here) how about using a barametric damper as the flapper?Bob Walker
*Since I'm loathe to encourage stooping to metaphors, & I have no desire to be pushing up daisies, let me try to clarify a bit further.1) The current situation, although not acceptable in my mind, has not killed anyone yet, which is why I'm treading cautiously here. I take CO poisoning seriously, which is why I have 3 separate CO alarms staggered inside the house: 1 by the furnace room, 1 by the stairs to the living area upstairs, 1 at floor level in the hallway in the bedroom area.2) I'm not going to put my faith in an "untested" mechanical device...it just seems that if there were something like that available, it would address some of the concerns raised by Fred re: backdrafting3) The furnace is already pulling air from the outside. The perimeter of the house in the area nearest the furnace (i.e. within 20 feet) is freezing. It's sucking air from the outside walls of the kitchen, entryway, & family room (& the 2 exhaust points I mentioned above), which is making the floors extremely cold. (I cannot get at these "leaky areas" very easily to seal them right now).4) What I'm suggesting is providing an air intake which will allow the furnace to pull outside air in along a path of lesser resistance. The vent pipe would be a relatively short length of steel or aluminum 3 or 4" duct, which terminates at floor level near the burners. I guess I'm having a hard time understanding why you think this solution would be worse than the current setup, in which the furnace draws conditioned air to burn, & sucks in cold outside air into large areas of the house to compensate for the negative pressure differential which results.Still curious, Per
*Maybe I'm confused. Please note that I am writing only as a longtime reader of this board, I have no experience.I just don'ti getit that the furnace's need for combustion air isi suckingin all this outside air. Does the combustion really needi thatmuch air? Fred mentions almost in passing attic bypasses. But, Fred, isn't that the problem here? If the attic is outside the building envelope, and ductwork runs through the attici and leaks in the attic, then that lost air must be made up and so is sucked in elsewhere.But Fred has confused me further with>The truth is that having the whole house supply combustion air is far and away the best solution. You get reliable, tempered, neutral pressure air without a big hole in the house. So don't isolate the heater with air barriers from the rest of the houseBut isn't one of the goals in weatherization to seal the basement ceiling. Isn't this then isolating the heater (if it's in the basement) from the rest of the house?Rich Beckman
*Rich,Just to clarify a bit further, the burner is in the basement (finished basement), and is within the heated "envelope" of the house. There is no ductwork in the attic; it all runs in the floors & walls, again inside the envelope. As for how much air the funace needs, it's actually quite a bit. I can't quantify it, but when you think about it, it needs oxygen to burn the oil, and all the exhaust gas that is generated from the burning exits through the chimney. As all that exhaust exits the house up top, air has to be pulled in to equalize the pressure (otherwise the exhaust gasses could back vent/ blow back into the basement). Right now, its pulling that air in from all points of the house. I'm suggesting putting in a "path of least resistance", so the supply air if fed almost directly to the burner, as opposed to freezing all the floors near the furnace room.
*Further to Rich's comments about "weatherization goals"/contradictions. . . in a well sealed house, small amounts of fresh air must be introduced continuously for the health of the occupants, as well as larger amounts, periodically, for heating fuel combustion. Negative comments have been made previously on this board about the usefullness and cost effectiveness of Air to Air Heat exchangers and other such mechanical devices, with suggestions that cracking a window would suffice.Does a draft from a cracked window provide better "conditioning" for air than a specific intake vent for a furnace??? Is it less of a "hole"? A window that is "cracked" can also be closed, accidently or on purpose creating a dangerous situation, not to mention the security aspect of such an arrangement. It would seem in this scenario that a specific vent for "combustion air" would be more appropriate. -pm
*Per Swede,Please don't misunderstand, I am not trying to argue the point. I am sure you know more about it than I do.But theoretically, couldn't the vent leak into the wall and the wall leak into the attic and so create an attic bypass?I remember reading elsewhere on this board that even a well sealed house still undergoes one to two air changes per hour. That seems like a lot of supply air to me.Rich Beckman
*....not for nuttin... what about a baffle box instead of a spring loaded flapper.??...rigged one up for a fresh-air inlet for a basement darkroom....the box takes the place of a standard basement window...you could run 6" duct to it and a nice wall jack on the outside with an insect screen.. and a location high enough to avoid the occasional snow drift...no flapper valve..do you think this would be subject to the same negative pressures??I really liked Fred's position on 100% sealed combustion appliances...in the meantime there's an awful lot of houses out there sucking a lot of cold air in thru inappropriate locations..tell me more about air - to air heat exchangers...Energy Star is pushing them big time...or id I fall asleep at the wrong time at the last seminar I went to...I was just getting ready to write them into a spec for a new house....let's see Ventaramma or Broan...Are "earth-tubes " out of the question when it comes to fresh-air inlets?
*MikeCheck the archives.. . lengthy discussion last winter. ..Gene Leger posted some testing data thast showed they were mostly a waste of money.i ". . . in the meantime there's an awful lot of houses out there sucking a lot of cold air in thru inappropriate locations..."this is the question that never quite gets answered. .. straight. "Seal the place up, and rely upon drafts", oh and provide at least .3 air changes per hour. Uh huh! Get used to the bafflegab. -pm
*....This was freezeup weekend for everyone who has become complacent here in RI...two mild winters in a row and every one forgets how to get thru it..Out on some service calls with my fav. HVAC sub and he's relating a commercial freezeup situation..2-storey block shaped bldg with a slightly pitched roof (really NO attic ..just a space near the peak) and a rubber membrane roof... a central utility core...with a stairwell terminating at the roof structure bottom....gas hot air..The GC for some unknown reason decided the roof space needed venting during the construction of the bldg....so he installed (4) 16" wind turbines into the roof space and sitting on curbs on top of the roof membrane...we're estimating that these things must move 300-400 cfm when the wind picks up...the Owner can't keep the heat up..plumbing fixtures are freezing...My bud has his guys tape plastic garbage bags over the turbines and the problem disappears...guess where the 1200-1600 CFM makeup air was comming from ?These are all intelligent people too... how do these things get done?...So Patrick...are we in agreement that the best way to introduce makeup air is to provide for it...wether it's combustion air or makeup air... or bath exhausts or central vacumn, or kitchen exhausts, what goes out must come in..do we want neutral,...slightly pressurized....or slight negative pressure....my gut says neutral is impossible, so plan for slight positive pressure and work to keep the moisture going out thru exhausts instead of getting into interior spaces where it's going to condense and start problems.....obviously (maybe NOT obviously) a NEGATVE pressure is going to be sucking rain water and moisture laden air into some very inappropriate locations....Which brings me to my quest...The MOST effective heating system for those who can afford it...I think GAS fired HOT AIR...1)ducted ..so I can control where the air is going and use it for central air in the summer2)I can filter it3) I can humidify it4) I can dehumidify it......If the house if one floor I would consider radiant slab with oil fired boiler...but I still don't have central air, and filtration, humidification , and dehumidification..Maybe FAN/COIL units ? talk to me..I wish this post was over on the heating /insulation section... but it's been taking so long to get from the opening page to the sub=sections that it's ridiculous..
*Mike - While heating a house in cold weather, you'll have neutral pressure somewhere in the house, positive above, and negative below. This is relative to the exterior pressure. I believe its desirable to lower the npp as much as possible - which goes along with your idea of sealing. But I'd rather not "keep the moisture going out thru exhausts" because with the moisture goes my heat and with all this air going out my house will suck in dry and cold outside air, requiring a humdifier to pump more moisture and so on as you've discovered by your recommendation for a humidifier.
*............Bill.. this post keeps falling off the board.. come on over to Heating and talk to us..look for b 'What the heck is wet heat?'I want you to tell us about npp... and what to do when you've got 10 fish tanks in the family room, and a steam bath in the master bedroom... I don't want none of that ivory tower stuff neither... I mean you've been in the house where the wall paper was falling off the walls, and there was mold in the closets in the middle of winter (and no we're not talking about wet crawlspaces, either)come on Bill... I'll tell you about floors with 1/4 " gaps in them.......
*MikeOnce again check the archives for Pressure Plane thread(s),but put on yer asbestos underwear, it got pretty hot there for awhile!! You tryin to stir it all up again you rascal??The best yer gonna hear from the "experts" is crack a window and put your bath fan on a timer!!-pm
*MikeI don't know what kind of volume we're talking about, but necessary daily airchanges, and fuel burning, and venting makeup air has to come from some where. Relying upon "drafts" from a shell that was supposedly carefully sealed or a "cracked" window just doesn't seem i scientificenough but if air exchangers, and/or vents into furnace rooms aren't acceptable, where the hell is it comin from????As far as your quest is concerned, opinions on this board lean heavily on Radiant Slab. I am not familiar with your term Fan/Coil... is that a Heat Pump?? That would look after "conditoioning", but requires ducts etc, a duplicate system.A heating and cooling expert I ain't, but after more than a year of this dance I'm still looking for some straight answers!!-pm