MUA systems can become quite elaborate, but it may be best to start with simple DUI approaches to see if they work well enough. You want the house pressure to not fall much or the fireplace will at best not draw properly. Fireplaces only draw as it is because there is normally a slight differential pressure between the hearth and the chimney exit. Say that you have a true 600 cfm going out, and some house leakage that we will assume is unknown. Then you need up to 600 cfm of make up air; more if there are also bathroom fans in use, or a dryer, water heater, furnace, etc. You could adapt the air conditioning intake ducting to pull in outside air when the pressure became negative. The issue is how much air will be pulled in through that path versus the house pressure. If it isn't enough (the pressure is still too low), then some additional flow is needed. This could be done by blowing outside air into the air conditioning ducts. This may work in very temperate areas where heating is not needed. A less lossy path might be considered where outside air is pulled in through a damper. Again, cold air may be a problem. A blower may be needed. Unlike commercial hood and MUA setups where the ventilation is usually run at a single speed and hence the MUA can be run at a single speed, the residential hood blower is usually variable. Balancing the system for various conditions, including open windows or not, bathroom exhaust fans on or off, etc., can be a challenge -- one I am still working on for my own system. Another stage of complexity is to heat the incoming air. This means another furnace circuit, or an electric heater and some large conductors. And all of this requires more ducting, a suitable intake assembly on the roof or exterior wall, controls, etc. Sometimes the physical configuration of the house makes such a system impractical (giving the benefit of the doubt that any MUA system is practical). You may wish to plan on open windows in a remote room that has a very good heating system to temper the air. A kitchen window can work, but tends to disturb the rising effluent of the cooking process, causing some to miss the hood. kas

"The closet the gas furnace is in, is not ventilated. The closet does not have a roof, but opens up into the attic. He does not think there is enough fresh air making it down to the furnace, and he does not think the fumes from the furnace are making it up into the attic." the closet is actually very well vented if it is open to the attic at the ceiling (roof?) of the closet. "He has instructed us to nail some gutter pipe (gutter pipe, because it is square, and will fit the limited space better than round pipe, but to mee gutter pipe seems awfully small diameter) into the closet to increase circulation. One peice going 12 inches into the attic, and another peice 12 inches off the floor. To me this seems awfully suspicious, I cant see how this will work, and I'm scared." I usually install a ceiling in gas furnace closets using ductboard (doesnt burn) from inside the attic. Usually a 5 or 6" vent pipe from inside attic..12" above insulation with a bug screen. the pipe goes thru ductboard ceiling to where the air intake of the gas furnace is located. I've started putting an inline manual damper..open when furnace is in use..closed for cooling season. "He also noticed that someone has stapled fibergalss insulation to the inside of the closet door, and we should remove that. That the entire door needs to be replaced with a very tight fitting door." Someone was trying to overcome the temp transfer from top of heating closet being open to attic. Bat insulation is not a good idea..but ductboard works well. and door should be weatherstripped. while the venting will supply the air needed for the furnace, it won't vent fumes. there shouldn't be any fumes if furnace is operating properly..there are vent pipes attached to the equipment that vent out of the roof. as for the smell...it could have been a sealant that he used or many things. I would call the original person who did the install and tell him your concerns. Granted there are better materials to use but it sounds like he/she was on the right track. better to close in ceiling and make it air tight and bring fresh air to the furnace than to leave the ceiling open to the attic. just my experience here in hot humid La. it may vary if your area is different. best of luck.

at the location my exwife and her new husband live now there was a similar problem several years ago. the older couple that lived in the OLD house called the gas company and the HVAC co to complain they smelled gas shortly after a new furnace was installed. neither company found anything and chalked it up to something dead. the older couple put up with it for a month, it got worse each day, spreading from room to room. finally it got so that they could smell it in the kitchen. well, the older lady went to fix supper one night, turned on her gas stove and BOOM! the whole house was literally blown to pieces. turns out that the gas co had a leak inthe underground line right before the gas meter. in no wind conditions the gas would work it's way into the house and slowly build. most of the time it dispersed before reaching harmful levels, but finally it built up enough that it exploded. she was killed, he suffered major burns over a large portion of his body, and even the neighbor's house was destroyed since it was only 20 feet away. if you even THINK this is gas, don't settle for "i can't find anything" MAKE THEM FIND IT! car exhaust does nto smell like rotten eggs. sewer gas does nto smell like rotten eggs. NG, LP, and rotten eggs smell like rotten eggs. a dead and decaying animal will stink, but again it is a different smell. if you want ot know what it smells like, go to the gas company, they can give you a whiff of a sample so you can tell if that is what you smell.

Keep in mind that baking soda, bowls of vinegar or vanilla do not work overnight and if the windows are open you're limiting the effectiveness of it. Essentially you're working on the whole outdoors rather than just the room. Vent the room for the major stuff and while people work in there, then close it up. It can still take weeks to absorb the odors. If they spilled it in there then you may well have to remove the carpet. If it's fairly new, possibly a square yard or so, (depending on how widespread the spill was) could be removed and replaced with new carpet so you wouldn't have to replace it all. I'm hoping it wasn't so much that it soaked down into the flooring beneath. If she spilled THAT much though and didn't say anything, I'd be having a very serious conversation with her. But back to the issue. Frankly, wouldn't it almost be better to pull the carpet with your sensitivities? If you don't have hardwood under it you could put a parquet, tile or vinyl down. Easier to keep clean, less dust and allergens and throw rugs could be used and tossed in the washer even in the event of a repeat spill. It just stinks (pardon the pun) that you should have to endure this. Whoever did this should kick in on the cost IMO, but of course that's up to you. I'm wondering about the carpet cleaning places though. Most use chemicals that could cause you trouble. There's one around here now advertising that they use activated water and if it works, that would be the route to go to avoid more irritants. Possibly someone could try a cleaning with vinegar water, let it sit a while and then use the charged water system. From what I understand, it works in a similar manner to an air ionizer. The water is electrically charged and dirt and the like has a positive charge so it's attracted to it. There's places selling the cleaner bottles that work this way now for "green" cleaning and I do know that ionizers work so I'm inclined to think this does have merit. Again I wouldn't count out a good ionizer. I have great experiences with them. Again, possibly a friend could rent a cleaner, especially a scrubber and use a vinegar water to absorb as much as possible. Then have the ionizer going with windows and doors shut. I used ionizers back when I smoked and people didn't know I smoked other than having ash trays out. Had a small 12 volt one in my truck too and my dad, who was a nut about smoking, had no idea. Also a friend's company has some that get used by cars or places that have had small fires in them and he cleans them up, puts the ionizer in there for a couple days and it's amazing what it can do. I'm talking about a good one, not a cheapie. Another thought or two. Check with a disaster cleanup place for ideas. They deal with fire and sewer smells all the time so they should know what it takes. Also you should find out exactly what perfume she spilled so you can contact the manufacturer, tell them the situation and maybe they could tell you how to neutralize it? Or if you know what's in it you could do some research on it. Lastly, I'm not sure if your or your guest's homeowners insurance would cover this so it could be a long shot but it might be worth checking it out, especially if you have to replace carpet and the like. Theirs might be more likely to cover it or possibly part of it. I understand your situation. I can't go into a room where people are burning scented candles anymore. I cough nonstop and people can be very insensitive about it. BTW, plain, paraffin, unscented candles, well any fire, candle, lantern, portable burner etc, will help absorb odors too. Obviously they shouldn't be left unattended. I'm just keeping my fingers crossed that you can get that smell out. I know how it lingers from someone being in an elevator a couple minutes, much less soaked into a carpet. Good luck and keep us posted.