Insulating plumbing vents and drains?
sayn3ver
| Posted in Green Building Techniques on
Is it worth the expense and time to insulate drains and vents? Essentially they are outdoor spaces inside your envelope? Just trying to decide before closing up some walls.
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Lance,
Drain pipes have no connection with outdoor air; they connect to septic tanks or municipal sewer pipes, which are below grade and generally fairly warm.
I have never heard of anyone insulating a plumbing vent pipe. The vent pipe only pulls in outdoor air when water is draining down a pipe, so the cfm flow of outdoor air is quite low. I wouldn't worry about it.
All drains are typically connected to a vent. There is no separation between the drains and vents. The entire house drain is vented to the outside typically.
I have a 4" main drain connected to a 4" vent. I have a 4" radon vent. All vent through roof.
I realize they aren't sucking in air actively. But the inside of that pipe is theoretically outside the conditioned space.
Lance,
If the air in a vent pipe is still, the temperature of the air in the pipe will eventually reach equilibrium with the temperature of the pipe wall. If the pipe wall is at 72 degrees F, the still air will eventually reach 72 degrees F, too.
As soon as you pull the plug on your bathtub, a small volume of outdoor air will be drawn into the vent pipe. Once the water has drained, that small volume of outdoor air will begin the process of coming up to indoor temperature.
I think Lance might be onto something here even though it is normally ignored. When the air in the pipe is at room temperature and it is cold outside, it will be lighter than the outside air. In a narrow tube, it might sit still despite that inversion. But in a 4" pipe, the hot air could easily slip out one side of the top while a pocket of cold air came in the other side, initiating a convection loop that could replace all the warm air with cold. The heat loss might be negligible when you have 2x4 walls sloppily stuffed with fiberglass, but it could be measuable in a pretty good or better house. As soon as it gets cold it would be easy enough to drop a temperature probe down a vent and see.
"easy enough to drop a temperature probe down a vent and see."
Charlie, If you look at the walls with a thermal imaging camera I don't think you see enough of a problem with vent pipes to justify messing around with them.
In cold/very-cold climates insulating the plumbing vent stacks increases the likelihood that the vent will become plugged with frost. Without a convective path from the conditioned space air to the stack (assuming the traps are all properly configured & filled), and the heat loss is very modest. But without the passive heating from where the stack runs through conditioned space the smaller convective loops inside the stack cool to the point where it condenses & freezes once it passes through the insulation layer.
http://www.structuretech1.com/wp-content/uploads/2013/02/Plumbing-vent-frosted-shut-three-inch-ABS.jpg
If insulating it causes frost problems, that means the insulation is doing something, which means that without it there is heat loss. If you've got a thermal camera, that's one way to get an idea of the size of the heat loss. We could also just make a guess like assuming that we have R-1.5 thermal resistance from the inside of the pipe to the house, and that the temperature inside the pipe is halfway between indoor and outdoor temperatures, which would be equivalent to assuming it's R-3. Then consider the area (10 square feet?), and you can conclude that the heat loss in on the same order as a double-pane low-e argon window. If you care enough about that window to consider triple-pane, you probably care enough about the vent loss to consider doing something about it.
Unfortunately, insulating it doesn't seem to be a good idea, based on Dana's picture.
An alternative is to use AAVs (air admittance valves) in conjunction with one other vent that can release positive pressure in the sewer line if necessary. Some passive house builders are advocating that approach. Others say that AAVs are less reliable than traditional vents. The argument that comes back is that yes, as vents, they are less reliable, but roof penetrations are notorious weak points and avoiding them is going to make the building as a whole more reliable.
http://www.ecobuilding.org/code-innovations/case-studies/plumbing-venting-with-air-admittance-valves
Charlie,
How many vents are we talking about? The house I just finished has one 2" and one 3". They both go through a foot or so of cellulose in the attic and into interior walls. If we had decided to insulate them we would have had to do not only for the vents but the two hundred or so feet of drains they connect to. I have no idea how you would even do that. What about where they penetrate wall plates or go through joists? What about drains not isolated by traps, like toilets? What are we talking about in terms of energy losses? We are chasing a solution to an insignificant problem.
Yes there is some heat lost, but it's a pretty small number. In less-cold areas where it normally gets above freezing a few times per week the frost up issue goes away, and if you really want to insulate the stack it doesn't create a problem.
But in those climates the amount of "payback" on insulating a plumbing stack is even less than in cold/very-cold climates. The insulation money would usually be better spent elsewhere.
That's all I was asking. Is it worth it? Because you'd have to do all the drain piping like mentioned.
Just seems like we worry about insulation levels else where and then pipe outdoor air to each fixture in uninsulated conduits.
I'm not going to worry about it for my own project unless people were recommending the added expense and time.
They are uninsulated conduits to/from nowhere, since there is no active air flowing, only modest amounts of convection in & out right at the top. It's nowhere near the same impact as an actual air leak that size, but even a 4" diameter air leak would have a fairly small energy impact, even if you lived in Antarctica. Most homes in the US built prior to the IRC 2009 air leakage standards have air leaks equivalent to a fully open double-hung window or two.
If your energy costs were $18,000 USD/MMBTU it might be "worth it", but if your energy costs are that high moving to a warmer climate would be a better investment. :-)
It seems that I'm being accused of recommending insulating vents and drain pipes. I don't think I said that although I might have implied it was a good idea. To be clear, I think the heat loss is real, perhaps on the order of the heat loss of one good double-pane window. If you could do something about it for less than the cost of upgrading one window from double-pane to triple-pane, it would be worthwhile if you think buying triple-pane windows is worthwhile. But it's certainly not going to undermine the energy performance of the whole house.
The only thing I see as a viable solution is AAVs, combined with some vent that can provide pressure release if needed. Is it worth the extra cost? Actually, my impression is that AAVs are cheaper than paying a plumber to run vents and a roofer to make the penetration waterproof, not even counting the need to airseal the penetration. So as far as I can tell, that's like if the window dealer said you could have double pane for the regular price or triple pane for a few hundred less. I think I'd choose triple pane given those options ... although if Dana is offering me the opportunity to move to a milder climate I might consider that as well.
Malcolm ,
ALL water closets have traps . That large surface of fluid you see within the toilet would be a trap . Vents with the exception of those connected to septics are not as inactive as is being portrayed . If you are connected to a sewer , your VTRs and your neighbors VTRs are in fact venting the public utilities sewer , unless one believes that the small 1" holes opposite each other on a manhole are sufficient vent for that huge system . This is why all sewer taps are made at or above the centerline of the main , so the vent is never rendered ineffective .
Richard,
Of course toilets are vented. They are "wet vented" so as you say, the trap is the bowl. My point was that if you are going to insulate everything before the traps you would have to somehow insulate the toilet too.
The active role of any building's vents in the larger sewer system is the reason building codes restrict the use of AAV's to very specific situations - meaning they aren't much of a solution.
Charlie,
No accusations from me, I'm just thinking through the implications of trying to isolate the drains. There are all sorts of building details that posters here worry about, like isolating interior footings from the slab, the thermal bridging of the nails in their sheathing - and vent pipes - which are too high hanging fruit to worry about. Rather than being in the order of energy loss of a window, they are probably more comparable to standing in an open door for a few minutes saying goodbye to guests, and completely dwarfed by the plug-loads and occupant behaviour of the owners.
We have pretty good idea as to what works to dramatically reduce the heat loss of building envelopes. Spending time thinking up solutions to things that don't make an appreciable difference just seems a waste of effort to me.
Which building codes restrict the use of AAVs with the exception that every dwelling must have one vent that is connected to the sewer and terminates in the open air ?
They certainly are a solution to the extensive series of piping running through walls in what are supposed to be very good houses in the fact that they certainly do eliminate a cold thing in your house problem , which might I add runs through the entire house from bottom to top .
A wet vent by the way is when one uses a drain receiving discharge from another fixture as the vent for a fixture other than the one it serves . All toilets are not wet vented . Some vents are dry and some are wet .
Q: Which building codes restrict the use of AAVs with the exception that every dwelling must have one vent that is connected to the sewer and terminates in the open air ?
A: Ours.
"A wet vent by the way is when one uses a drain receiving discharge from another fixture as the vent for a fixture other than the one it serves ."
What made you think I needed an explanation of what a wet vent is? And no not all toilets are wet vented, but dry vented ones still rely on the bowl to keep sewer gases out, so I'm not getting your point?
What you haven't done is offer any explanation for why we should worry about this at all.
Ours is very vague Malcolm . Which code do you use and what state or city do you reside in ?
I did not think you needed an explanation but posted one for others whom may not know and so they could be informed and not go forward thinking all toilets are wet vented as you stated .
I did not offer an explanation because I too believe it is just a bit much minutia to be concerned with , but then again can see the point in asking the question .
I didn't mean to create such an issue. I was merely pondering while running some electric if anyone has done it or recommends it? I'm a commercial electrician and I believe the only time I have seen it done was on some huge 8 or 10" drains handling runoff from the flat roof. I'm almost sure they did it for two reasons...
1) for sound deadening since the drains were near a store entrance.
2) they were cast iron due to the plenumn ceiling and the insulation might have allievated any swesting as these drains were boxed with drywall below the ceiling.
Lance,
Sorry. It was an interesting question well worth discussing. Martin and dana gave you good advice. Sometimes discussions of things that turn out to be pretty inconsequential take on a life of their own here. It's really my problem if I find them annoying, not anyone else's.
Richard,
I live on Vancouver Island. We use the BC Plumbing Code, which is a regionally amended version of the national one. Except for very specific situations, such as kitchen islands that can not be vented conventionally, AAVs are not allowed in new contraction here.
Malcolm ,
just so you are aware , I was not defending AAVs , On occasion like an island sink like you stated , I may use one , but as a norm I still run VTRs . I guess the other problem would be a US vs Ca codes .
A cold water drip (let alone a hot water drip) from a leaky fixture running out the drain will probably waste more heat energy than the conduction and convection of HVAC conditioned-space heat through the vent stacks. And if your on a septic tank, you might get some heat gain (exchange into the PVC) as a result of the heat rise out of the tank as it passes through the piping. In fact, a temp read on the vent stacks might tell you more about the free heat production than the building heat loss.
Investing in tank heat capture might pay off.
http://solarenergyengineering.asmedigitalcollection.asme.org/article.aspx?articleid=1455940
In our neck of the woods (Vermont), it is required by code to protect the vent stack from freezing. Horizontal runs are covered with insulation bats in the attic, usually.
Of course, all penetrations where drainage or vent pipe goes through walls, especially into attic, should be sealed around the pipe to prevent infiltration. Also required in fire code for commercial to prevent drafting/spread of fire.