Replies

1. 
   rdesigns | Jan 07, 2010 02:10pm | #1

   If you feel there's no need
   If you feel there's no need for additional combustion air in the mechanical room, the easiest and cheapest thing would be to install a supply register (say, a 4 x 10) on the side of the supply duct or supply plenum.

   Test for how much you need to open the louvers on the new register by doing the blown-out match test at the door bottom(s) to see when the air begins to move out of the mech. room instead of being drawn in.

   You could also install 4" duct from the outside that connects directly to the return air of the furnace, along with a manual damper to allow you to control the flow. This arrangement would pull in outside air anytime the furnace runs, which are the times when, currently, the furnace de-pressurizes the space.

   You can get more complex by using a motorized damper that's tied into a timer, or other methods, but I always tend to go for the simplest fixes first. My first suggestion may do the trick--if not, you've lost very little money or effort.

2. 
   rjw | Jan 07, 2010 02:41pm | #2

   >>My fear is that the furnace is sucking up radon and distributing thoughout the house because of the negative pressure in the room adjacent to the crawlspace.

   There shouldn't be any returns in the furnace room or, if I understood your describing, in the area with the potential high radon.

   I don't see any reasons to "pressurize the house other than to waste heat {G}

1. 
   popawheelie | Jan 07, 2010 03:29pm | #3

   My furnace is a high effecience 2 stage furnace.

   The combustion air is pulled in from outside.

   But, when it is on it pulls the door closed to the room.

   So, why is it pulling air?

   Rdesigns has said before that HVAC systems can be out of ballance. The air retuning and the air going out of the furnace aren't equal. So the furnace makes up for it by pulling air from the room.

   Also, the ducts run through the crawlspace and if the returns are at lower pressure than the crawlspace they are picking up radon in there.

   Rdesigns can elaborate on this. I'm kind of scetchy on this whole area.

   A house has leaks. Some leaks are going in the house and they are cold drafts you can feel. Some leaks are going out of the house but you don't feel those. Either way I am loosing heat by cold air coming in or warm air going out.

   If my house, overall, has a negative pressure, it is pulling outside air into the house. It will find a way in.

   Since my house is three stories there is a stack effect and the air leaving the house through openings in the third story cieling is pulling air in from other areas.

   If the basement has openings to the crawlspace and under the slab this negative pressure is sucking in air with radon in it.

   This is in the heating season.

   If I run a duct from outside to the return of my furnace it will ballance that. Then I need combustian air for my water heater and makeup air for my clothes dryer. They are all in the same room. So I run a duct from outside to them in the room.

   But I still might have a negative pressure in the whole house. Especially in the basement where there are radon gasses being pulled into the house.

   I can easily put in makeup air for the furnace return, the water, and the clothes dryer. I will do those two things.

   Should I do anything else?

1. 
   rdesigns | Jan 07, 2010 06:01pm | #4

   As you noted, houses can be subjected to pressure imbalances either by passive (stack effect) or by mechanical means. A 3-story house like yours will--in the heating season--see a stack effect even if no fans are running.

   The operation of fans can either increase or reverse the pressure differences created by passive means. And the big fan always wins. In most houses, the big fan is the furnace blower.

   Without seeing your house, here's what I suspect is happening: the furnace room is being de-pressurized due to 2 causes. 1) Leaks in the return air ducts and/or stud/joist spaces that are used for returns. These returns are probably enclosed in furr-downs and chases that eventually open into the unfinished ceiling of the furnace room. Such furr-downs and chases become, in effect, a vacuum tube that is sucking air from the furnace room and from holes that open into the crawl. 2) the other factor is probably insufficient return air in other spaces in the house. If so, this makes the leaks in the return system even more powerful as the duct system tries to balance supply and return flows.

   My earlier suggestion to add a controllable supply register in the furnace room will greatly help to balance pressures. Also, you could add a large (12 x 14, or so) grille that effectively opens the furnace room to adjacent spaces. This would also help give the dryer a better source of make-up air.

   Next, you could cheaply and easily add a source of controllable outside air by running a 4" or 6" duct from the outside to the return air plenum. With a manual damper. This will allow you to fine-tune the amount of OSA.

   Lastly, with the furnace blower running, go to each room that has a door that can be closed, and do the match test at the bottom of the closed door. If the airflow shows you that the room is being pressurized, you need to give that room an unrestricted path for return air. (Undercutting the door, transfer grille, jumper duct, etc.)

   If passive migration of radon gas is a continuing concern after you do these things, you can move air from the crawl to the outside by either pressurizing or de-pressurizing the crawl with a small fan. The more effective way would be to de-pressurize it by having the fan blow to the outside. 20 CFM would be plenty.

1. 
   popawheelie | Jan 07, 2010 06:30pm | #5

   Thanks rdesigns, I will be doing all of the above.

   I think there aren't enough returns in the house.

   They are harder to run and maybe installers don't think they need that many. Whatever the case, I will be looking to balance it out.

   I found an interesting article on radon abatement.

   http://www.inspection-perfection.com/main/pdf/Radon%20-%20confusing%20issue.pdf

   I'm going to try a passive system for venting the crawlspace first. I can always throw on an inline fan.

   The reason I wanted to pressurize the furnace room was to kill two birds with one stone. But separating out the issues sounds best.

2. 
   rjw | Jan 08, 2010 10:13am | #10

   There are two separate "air streams" going through the furnace:

   1: the air which is heated and distributed through the house (the conditioned air "loop"); and,

   2: the air which is consumed by the combustion process and expelled as flue gases from the house through the flue.

   Assuming your combustion air supply is properly sized and installed, (check the manual which the installer was supposed to leave):

   Then, the negative pressure which is pulling the door shut is from the return side of conditioned air loop: there must be openings in the return in the utility room.

   A good installation, IMO, has a cover over the filter slot and the return ducts junctions are sealed.

   Note 1:

   Although not applicable for your system with an outside combustion air source, folks with other systems (either older furnaces with draft hood or so-called 80+ induced draft systems which use house air for combustion) should know that "significant" high negative pressure (certainly enough to pull a door closed, and actually, much less than that - the only way to know is with a draft gauge) in the utility room/combustion zone can cause "backdrafting" where the flue gases (including carbon monoxide) are pulled into the room's air and then into the return system and then circulated through the house.

   Note 2: the amount of "air pressure"/draft in an "standard or 80+ system is about equal to the amount of "air pressure" it takes to blow out a match a couple of inches from your mouth - that is, not much.

   Note 3: in an 80+ induced draft system the fan does not push the flue gases out - it merely stabilizes the combustion air/gas flow/movement through the heat exchanger, allowing the burners to be designed for more efficiency (rather than being designed to work with a wide range of movement of the combustion air.)

1. 
   rjw | Jan 08, 2010 10:34am | #12

   A "standard" "low efficiency" furnace with a drafthood:

   View Image

   ======================================================

   ======================================================

   A mid-efficiency 80+ induced draft furnace will have some sort of grill in the burner compartment cover (the 2 upper grills, partially cut away in the image below*), will have a metal flue (not PVC plastic) and will not have a condensate pipe (usually white plastic PVC starting at the bottom of the flue:

   View Image

   ======================================================

   ======================================================

   A high efficiency 90+ furnace will have a plastic flue (if it is gray plastic, it is probably a recalled material and must be replaced - white plastic is most common [in my area], black plastic is sometimes used) and a plastic condensate drain line from the bottom of the flue to a drain (not to be confused with the A/C condensate line)

   --------------------------

   --------------------------

   * Important note -in the 80+ "mid-efficiency" draing, the cold air return is shown as a louvered cover to the fan compartment on the front of the furnace

   This is wrong and dangerous: Building codes (generally) prohibit any return air openings within 10' of the furnace, and there should not be a return on the furnace housing itself - that can cause dangerous flue gas backdrafting and will cause it in all but the loosest construction.

3. 
   Matt | Jan 07, 2010 08:17pm | #6

   I think you should install a 4" or 6" make-up air duct into the room from outside. The duct could have a weighted damper so that it will only open when air is needed in the room. Then seal up the doors, etc. It will stay warm enough in the room just based on the ambiant warmth from the furance.

   Then install a simple radon mitigation system which is basically a pipe that sucks air from under the slab (pipe is sealed where it comes through the slab, and then exhausts this air outside. If there was a air path from the CS (which I'm assuming is vented) to under the slab it would be really good. That way you would be getting some air changes in the CS too potenitally getting rid of more radon. You said that the radon is at the Federal limit.... Are you aware that the limit was lowered not too long ago? It is now either at 3 or 4 - I forget which.

1. 
   popawheelie | Jan 07, 2010 08:47pm | #7

   I'm pretty much going to do
   I'm pretty much going to do what you said. I think the fed limit is at 4. I can do the work and test again.

   did you read the article in my last post?

   http://www.inspection-perfection.com/main/pdf/Radon%20-%20confusing%20issue.pdf

   I found it informative and NOT biased.

   Most of the stuff I read is trying to sell you something and alarmist.

1. 
   dude | Jan 08, 2010 06:52am | #8

   when my new high efficiency oil furnace was installed , installers said i needed makeup air so i installed a dryer vent through the wall after removing the flapper and substuting hd screening

   then i hooked on insulated duct & ran it over to where the furnace burner is

   the end of the pipe goes into a 5 gal can about 1/2 way down

   the above setup sure cut down on the drafts i had before in the enclosed utility area , ps building is all stone 30 x 60 2 stories circa 1873

2. 
   Matt | Jan 08, 2010 08:35am | #9

   poppa - off topic suggestion: change the font or something on your tag line. Everytime I read one of your posts I start reading the Will Rogers quote since it is not visually seperated in any way from the rest of the text.... I only needed to read it once... :-)

1. 
   popawheelie | Jan 08, 2010 10:25am | #11

   Got it. I can do that and never get off my butt. ;^)

3. 
   rjw | Jan 08, 2010 11:40am | #13

   Technical nitpick: the feds recommend 4 pCi/L as the action point for active remediation - deep in their information they also recommend action below that point/measurement

1. 
   popawheelie | Jan 08, 2010 11:57am | #14

   Did you read this? http://www.inspection-perfection.com/main/pdf/Radon%20-%20confusing%20issue.pdf

   I found it refreshing. The author was questioning a lot of presumptions.

   The feds might be full of beans. But I will do the right thing regardless of what others think. I've always found that if i try to do the right thing most things will work out.

   Fear is a very effective tool if played out well.

1. 
   rjw | Jan 08, 2010 01:31pm | #15

   Interesting link, thanks.

   My understanding (based on info that used to be on the EPA's website years ago) is that the 4 pCi/l standard is based on extrapolating from figures derived from studies of miners who were exposed to very high levels for long periods of time, and that the extrapolated figure of 4 assumes a straight line into the extrapolated area.

2. 
   popawheelie | Jan 08, 2010 01:45pm | #16

   There's a lot of
   There's a lot of extrapolating go'n on there! ;^)

   I figure like most things there is a limit to science.

   Unless you are scientist getting paid for extrapolating.

   Same thing for statistics.

   I've found that most of the time statistics are used by people to advance their agenda. Well math doesn't lie. right!