Insulating Ducts - Worth the Effort?

[ERPARKER]

My wife and I were very excited when the temperature finally plummeted on Saturday here in Northern Virginia. We turned off the furnace, stoked up our newly installed Lopi Declaration and it started pumping out the heat. As I feared, however, the layout of our house is far from optimal. The living room, where the insert is installed, is nice and toasty. I came in once and found our cat on her back with her belly pointing towards the fire. Our kitchen, however, which is on the other end of the house was down to 55 degrees by Sunday morning and there seemed little I could do to warm it up. I turned on the blower in the forced air a/c system to try and redistribute the heat but was disappointed in the results. Using an indoor/outdoor thermometer I stuck the outdoor temperature probe into the duct. The temperature did seem to change based on how hot I was running the Lopi but the range was on the order of 59 to 61 degrees! Still too cold. Two other rooms were also very cold.

Ignoring for the moment the placement of vents and feeds, what kind of results have folks had with insulating their ductwork? Much of our ductwork is standard uninsulated sheet metal that runs through our accessible, but unfinished basement which is typically in the 55 degree range in the winter when the furnace isn't running. I'd have to get out a flashlight to check on the runs through the crawlspaces. I would expect to see some improvement by insulating, but can I expect to see a significant improvement?

 

[carpniels]

Hi ER,

your story is exactly the story of my winter. Same problems, same heat distribution issues.

I am actually insulating my heating ducts as we speak. Not only for the free heat of the stove, but also so that when the furnace kicks on, I do not have a lot of heat loss in the basement. It is a lot of work, but I believe well worth it. I am using the reflectix insulating foil. Easy to cut to size and tape.

In the mean time, I have fans strategically placed in the house that bring the heat where it needs to go. That works quite well.

Carpniels

 

[elkimmeg]

If you were to cut one inch strips out of the foil bubble wrap insulation apply them first say ever 16" instead of R4.2 with that dead air space it actually increases you R value up to R6. Which if you are using heat and Ac is where you should be. Insulation quites the system and reduces condensation of you exposed ducts in the cellar during the summer. By reducing condensation, you also retard Mold and mildew growth. If for no other reason, that has to be considered. Without insulation you are wasting fuel developing heat, that never gets to the living space. With combined heat and AC, you will save enought money, you could have paid for the insulation 10 times overin the first year. The first poster actually gave the best reason for insulation. Imagine the amount of wasted heat before it gets to your living space. and the drastic reduction or heat loss even before it arrives?

Besides fans. has one thought how to install a zone damper in their system, to move heat where you want it. With a zone damper, it opens and closes and directs heat to only the where you place the second thremostat. A perfect solution to those back rooms. I know you are still using the furnace but only for a limited area. and a limited amount of time. Then place box fans to move the cold air from those areas. Which will draw some of the stove heat there maybe not all that is needed, but some which will delay your thermostat from constantly calling
Insulation, zone damper, and box fans, will solve your delimar and save you quite a bit of money

 

[begreen]

Yes, you will see a significant improvement, especially if the job is done well. Before insulating, seal all pipe joints. Don't use cloth duct tape. OK to use the shiney aluminum tape. (Get this in large rolls from heating supply house. The little rolls are obscenely expensive.) Then insulate. Your mileage will vary with the fuel system and length of runs. Typically heat-pump systems see the best benefit due to lower warm air temps. Long runs through unheated spaces will show the maximum benefit. Do them first.

 

[scfa99]

If you were to cut one inch strips out of the foil bubble wrap insulation apply them first say ever 16" instead of R4.2 with that dead air space it actually increases you R value up to R6.

ELK, i'm not following the 1 inch strips. So you shouldn't wrap all of it? just every 1 inch for every 16 inches? How does that work?

 

[roac]

There is no doubt that insulating is good and is actually tax deductible this year and next. But with that said it will not help enough to aid in the heating of those other rooms. When your furnace is on the air that is in the ducts has been super heated well above the desired temp set point, the reason is obvious, less time to heat up your home. The problem with a forced air system when using a wood stove is being able to get warm enough air into the cold air return. To get it to truly work correctly you would need to really warm up that room where the cold return is and if you have more than one then you can forget it as it will be mixing with that cold air. Whenever you use fans whether it is the furnace fan, box fans, or ceiling fans is that the air needs to be really warm or you will have a wind chill effect. Tell the cat to move over and warm yourself in front of the fire!! :lol:

 

[elkimmeg]

cut and apply the 1" strips first then wrap it the over the strips. It creates a dead air space, which add to the insulation value
It now becomes a system value or R6.0 instead of just R 4.2
B green also aptly pointed out to seal the joints with HVAC tape first.
If you look at the air bubble foil wrap you will see 1" spaces in the wrap to cut the strips

This only applies to the foil bubble wrap product not the fiberglas wrap

Fiber glass one should use 1.5" or an r value greater than 5.0

 

[ERPARKER]

There is no doubt that insulating is good and is actually tax deductible this year and next. But with that said it will not help enough to aid in the heating of those other rooms. When your furnace is on the air that is in the ducts has been super heated well above the desired temp set point, the reason is obvious, less time to heat up your home. The problem with a forced air system when using a wood stove is being able to get warm enough air into the cold air return. To get it to truly work correctly you would need to really warm up that room where the cold return is and if you have more than one then you can forget it as it will be mixing with that cold air. Whenever you use fans whether it is the furnace fan, box fans, or ceiling fans is that the air needs to be really warm or you will have a wind chill effect. Tell the cat to move over and warm yourself in front of the fire!! :lol:

Thanks ROAC,

This pretty much matches my experience. The forced air system (used only for air conditioning) has just three returns, one on each floor and one in the basement (which is almost always closed). For one of my experiments, I closed all but the one return nearest the stove (but in a different room). I could immediately hear the blower motor straining so stopped that experiment ASAP and accepted that I was going to have a mix of warm air from that room and cooler, but not cold, air from our bedroom upstairs where the other return is located. The "wind chill" affect is also significant though I was thinking of getting plastic deflectors for the vents where this is a problem.

Based on the other responses, it sounds like insulating the ducts will be on my long-term projects list instead of my short-term projects list.

Eric

 

[ERPARKER]

cut and apply the 1" strips first then wrap it the over the strips. It creates a dead air space, which add to the insulation value
It now becomes a system value or R6.0 instead of just R 4.2
B green also aptly pointed out to seal the joints with HVAC tape first.
If you look at the air bubble foil wrap you will see 1" spaces in the wrap to cut the strips

This only applies to the foil bubble wrap product not the fiberglas wrap

Fiber glass one should use 1.5" or an r value greater than 5.0

Thanks for the info Elk,

This explains why I couldn't find the "separators", that the Refletix web site talks about, for sale anywhere. I would have been looking all over for these.

Eric

 

[carpniels]

Hi Eric,

I also was confused about the separators. I called reflectix and they told me to cut them the same way Elk did. I also first taped the sections before insulating them.

About your straining fan: check if you can set it to a lower speed. I am going to insulate first and then test the different options of the fan. but mine has separate settings for speed so if you have that too, change the speed to slow and it will not strain to suck in air if you only leave one return open. Better is to change the return to the ceiling so it will suck in the hottest air in the room. That is one of my long term goals.

Carpniels

ps. ELK. I hope you are right about the sound deafening. My forced air system is loud and wakes me up at night.

ps. Be green is correct about the price of the alu tape. Home cheapo has the small ones with 50 ft for $6 and high's has the 120 yards for $16. A no brainer.

 

[elkimmeg]

For sound deadening chose Fiberglass insulation the foil air bubble will help some but not as much as fiberglass

 

[scfa99]

ELK,

Awhile back you mentioned you wrapped your hot water heater. I have a 75 gallon WH and can't find an insulation kit anywhere that fits 75 gallons, even looked all over the net. Anyone have any ideas?

For wrapping the vents with fiberglass. What r value fiberglass should i get and is in rolls like the attic insulation?

As always thanks

Matt

 

[saichele]

Might try just closing the return inthe warm room, and the vents in the cold rooms. That way you're sucking cool air from the distant areas and pulling the warm air through the living space, not the uninsulated basement or attic. Downside is that you're blowing cool air into your stove room. It all depedns on your layout, but I've found that works pretty well to warm the cool rooms and cool the hot rooms.

Steve

 

[saichele]

SCFA-

I got a big foil backed fiberglass blanket from Menards for about $20. Went around a 50 gal with a lot left over. Might be enough for you.

Steve

 

[ERPARKER]

So I advise to give up on the central fan method of heating the house with the wood stove.

Yeah, and I figured that I wouldn't be getting any heat out the other end until I'd warmed up all the ducts between the return and the vent.

I'm inclined to think that insulating the ducts is still worth the effort, especially since we plan on living in this house for at least another fifteen years, but I'm not going to set high expectations that it will make a big difference with the wood stove generated heat.

 

[carpniels]

Hi ER,

I concur. I am insulatating the ducts to save money when the furnace is on. And I will try the wood stove air diversion with the furnace fan just to experiment a little. I might even go so far as to install a special return at the top of my stove room. That way 150+ degree air is sucked in and distributed (if I close all the other returns). Another fun experiment!!

Carpniels

 

[hydestone]

One other thing to keep in mind is that you don't actually "lose" heat in your crawl space (if it is in fact air tight). There will be a net heat gain in the crawl space which will radiate up through the floor. The gains will appear minimal however as they are distributed over a large area rather than distributed through diffusers to select areas.

 

[ERPARKER]

Another fun experiment!!

Carpniels

Just don't burn down your house.

I take it you decided not to go with the Declaration. You had expressed an interest before.

So far, all of my experimentation has been with the stove, what kind of scrap wood I can use to get the fire going, and how well firewood stacked uncovered for five years burns. I used to throw away my small wood scraps (no treated, no plywood) from my other various projects but now I use them as kindling. I also have half a box of tongue and groove cedar planks (from a completed closet project) that seem to burn pretty well.

 

[michael]

Hey, insulating is good, but, as I've noted previously, a central heat duct system will not heat via a stove unless the ducts are in a conditioned space, which is not usually the case.

Why? Simple - the unheated ducts act as radiators and radiate your room heat into your unheated basement.

If your basement is 55, R-6 ain't gonnuh make enough of a difference. 75 degree room air passing through 50 or so feet of cold ducts and a cold massive furnace is not going to come out at 70. Add the moving air thing and it's a lost proposition.

So I advise to give up on the central fan method of heating the house with the wood stove.

I agree with Frank on this one and go a step further. In my experience, insulating your duct work in an unheated basement is just a waste of time and money. You may actually achieve very small gains using your central heating system, but I have never been able to measure the difference. Once your ducts cool off between cycles, they have to start at room temp again. Insulation can't keep the ducts warm and toasty between cycles.

Wrapping your water heater is another matter. It is constantly heating and trying to maintain that set temp. Insulation will help here

 

[elkimmeg]

I guess condensation using Ac in the summer is not an issue in your basement? . Mold and mildew does form in moist enviorments.
that metal joist pan bay is an ideal magnet for condensation, for that matter exposed metal duce work as well. The truth is insulation is more important to cold AC in than heat. Insulation becomes even a larger component of energy saving for AC than heat.

Supply = returns for a balanced system. Eliminating returns which usually are not adequately matched or in ceilings or not optium locations to get heat distrubuted from the wood stove balance is thrown out the window. Do you really think it going to work?

Returns are meant to remove cool air which heavier if you remove the heavier air then you can drawn in lighter warmer air.
The worst location for returns is in the ceilings you are returning heated air there is no way to draw out the heavier cooler air at floor level.
If code would allow me there would be high low feed and returns for combined ac heat systems.
Then there is the issue of proximity of removing available combustion air of the soild fuell burning appliance. There is a chance that removed air is made up by drawing exhaust from the appliance. Closing down other returns to draw over the stove increased the risk of drawing in co and co/2's. . As you are re-desigining your systems supply = returns and casting all safety to the draft. I just wanted to point out to you heat HVAC engineers, there are a few dymanics you have not factored in. No I am not a design engineer, I'm the guy that sees poor designing and installations every day. Be carefull of what you do.

Did you ever wonder what it takes to heat or cool a room? A little more than placing one 6" duct here and there is involved. First one has to factor the temp as it leaves the boiler then reduction of you main trunk line to maintain pressure. to finnaly using 6"7" 8" 10" feeds and how many and their locations ( 4 or 5" for bathrooms), Factor in the same vollume for returns. Then there is the difuser and it pattern of distributing an air flow. One has to calculate the room vollume and the heat capacity of the ducts and then the CFM flow under the lbs of pressure applied. Many burmers have pully systems where a different pully connection will either turn the blower motor faster or slower, meaning if needed higher velosity can be used. This is only part of the complexities involved. So while you are re-engineering your ballanced systems, Eliminating returns?? I'm shaking my head just wondering about thought process