Hot Ducts Running Against The Roof Are A Common Massachusetts Ice Dam Problem.

by Insulation Geek | Nov 9, 2018 | 0 Comments

If you live in a Massachusetts home and are serious about solving your ice dam problems, once and for all, this article is a must read.

Very often homeowners that have central heating or cooling systems with ducts in their homes, call us about one of two things:

"I have ice dams in the winter that lead to cascading sheets of ice running down the exterior walls of home home and bring water leaks in through the ceiling and interior walls" or "I just can't seem to get my home cool enough in the summer and my nest thermostat is constantly at war with my central cooling system."

So what seems to be the problem? Well, to begin with, its always good to follow sound building science principles, where we take the whole-house approach to look at the entire home as one big connected box. Our goal as homeowners is to keep this "box" at an approximate temperature of 68F in the most efficient manner. Why? So we're comfortable. Human comfort is a major factor in home insulation, energy efficiency and HVAC design. This seems to be sometimes forgotten when chasing energy efficiency numbers.


inuit-hunter-insulationHuman comfort away from home...


So how did we prehistorically stay comfortable in our homes? We insulated ourselves, not the home. We actually wore warm clothes, sheep's wool, bear skin etc. even at home, to keep our 98F body temperature as close to 98F as possible. A quick look at the inuit people today in Alaska is very telling indeed.


home-insulation-sheeps woolHuman comfort at home...



With the advent of the chimney fireplace and wood stoves, we were able to then burn fuel sources like wood, to generate (possibly) enough heat to bring the home to 68F or so, to stay comfortable while exhausting the carbon monoxide outside the home. 


home insulation chimneyHome HVAC system with an exhaust...


The typical amount of radiation from a fireplace depends on a variety of factors. Everything from the type of fuel used to the size of the fire plays a role and so the temperature can be as low as 500F all the way up to 1100F. Imagine that! Talk about a non-efficient heating source for the home. Just to keep our homes at about 68F, we needed to have our heating source at about 800F (x̄ ) mean temperature! 


chimneyA very inefficient HVAC system...


Now think of the central HVAC system as this fireplace or chimney but its much more energy efficient when compared to this old fireplace. Even a conventional gas furnace is about 140F to 170F at the supply plenum. So that's right at the unit. So if you walk right over to your unit now, imagine this 140F heat blowing right out of it to get our homes to the 68F. For a high efficiency furnace this could be as low as 110F. 


hvac causing ice dams in atticThe modern fireplace, sans chestnuts...


Now see those giant ducts coming right out of the HVAC unit? They're carrying this 110F - 170F heat right out to the different parts of the home like tributaries. What is the duct wrapped with? Duct wrap insulation. Made specifically for HVAC ducts. What is the duct insulation made of? Well there a few different options out there ranging from fiberglass duct insulation wraps to bubble wrap duct insulation wraps. Some ducts even come pre-insulated with the wrap around it, to be installed directly by the HVAC insulation technician, when installing the HVAC system. Here a few examples of duct insulation wrap that is insulating your ducts to and from your home's HVAC unit right now:

BUBBLE WRAP HVAC DUCT INSULATION - this is an alternative to the more traditional fiberglass insulation duct wrap. The idea being that its okay if it gets compressed during install and can fit on snugly around the duct. The air bubbles do the actual insulating. This is not unlike the bubble wrap insulation we get from our Amazon packages at home. In fact a few companies manufacture both, packaging insulation as well as duct wrap insulation.  

bubble wrap duct insulation reflective hvac

With an R-value of 6.0 - 8.0 per inch (these are rarely thicker than an inch), the have been used to insulate hvac ducts for quite some time now. 

FIBERGLASS DUCT INSULATION WRAP - This is the more common traditional fiberglass insulation duct wrap we see in most homes with HVAC units in the attics or basements. 

fiberglass insulation duct wrap massachusetts

Going over to your HVAC unit right now, there is a very good chance that either pink or yellow duct insulation wrap like this is what is installed around the ducts. There are actually four types of fiberglass duct insulation - fiberglass duct liner, fiberglass duct wrap, fiberglass duct board, fiberglass commercial board. 

The highest rated duct insulation typically available in residential applications is R-11. The R being unit of measure of resistance to the heat loss that occurs. So essentially the R-11 is what is supposed to keep the 110F-170F heat from that HVAC unit from being lost (somewhere). Its a phenomena called line loss or transmission loss. The idea being that its more efficient to wrap the duct with insulation so that the heat isn't lost through the ducts on the way to the room you want to carry the heat to. There is a reason we are talking about this and if you're serious about solving ice dams problems, this is important to understand

So where does this heat loss occur? Well, it depends on where the ducts are located as well as what the temperature difference is between the inside of the ducts and the outside of those ducts. The temperature difference plays a huge role in the heat loss through ducts. So when the HVAC ducts are located in the cold attic, in the winter, we expect R-11 insulation resistance to stop the 110F-170F heat from the ducts from escaping outside? Likewise, when the AC ducts are located inside the hot summer attic, can we expect the 120F or 130F Massachusetts summer heat in the attic, to not penetrate the cold air blowing from the AC, through the R-11 ducts? The line loss occurs indeed when the ducts are running through the attic struggling to get the insulation to your home. Moreover, insulation on the attic floor seems to exacerbate the issue.


check+forced+air+ducts+in+the+attic insulationHot ducts losing heat in the attic and melting the snow on the roof...


That's like installing the chimney outside the home and expecting the ducts to get the heat into your home indeed! Nope, it actually gets lost in the attic. Now, in the Massachusetts winter, when we have snow sitting on the roof and its 20F outside with the ducts blasting this 110F-170F heat into the attic, the snow starts to melt at a faster pace than the sun's rays melts it, while the snow at the gutter isn't melting as now heat is able to get to it. This often leads to ice dams. PLEASE NOTE: there are other reasons for ice dams too but this is a major contributing factor, particularly in Massachusetts homes.


IMG_5126HVAC units and ducts often squeezed right up against the roof in tight attics spaces are a major cause of ice dams...


Why is the R-11 point important here? This is because the R-values for home insulation in Massachusetts are determined by the Department of Energy. The current Massachusetts building insulation code for attics for example is R-49. So that means that you as a homeowner must know that the Department of Energy has determined that to keep the 68F temperature heat in your home from being lost to the outside winter temperature in Massachusetts of 20F, you need a resistance of R-49.

So again, that means the Massachusetts building code states, STOP 68F from bring lost to 20F by using R-49. Then how can we stop 110F-170F temp heat from being lost to the attic that is supposed to be at an approx. 20F winter temp by using R-11? PLEASE NOTE: R-11 is the highest available duct home insulation on the residential side, reality is closer to R-5. 

We are not talking about common duct insulation system failures either. This can range from fiberglass insulation being compressed, zip ties being loose, duct tape peeling off, cuts and holes in the ducts itself etc. Human variables can play a major role in determining duct insulation effectiveness too.


hvac duct insulation installs

Heat loss from duct leaks commonly occur from installation mistakes as well...


We are talking about the ideal situation and still we have major heat loss. Particularly when we have hot ducts right up against the cold roof as we recently saw in this Brookline, Massachusetts home insulation project:

IMG_5131Hot Ducts against cold roof causing ice dams in Brookline, MA 


When a client calls us up for an assessment of their home for ice dam issues related to insulation or HVAC, one of the first things in our checklist that we look for is understanding the existing HVAC unit and ducts plan. Are the hot ducts running right up against the roof causing the snow to melt through major heat loss into the attic?




IMG_5128Further HVAC and insulation investigation in this Massachusetts home...


During the actual insulation project, we chase your ducts. This means we follow them right from your unit to the outlet. We want latitude to be able to solve the problem and when agreed upon prior, this allows us to work for you to solve the ice dam problem. Sometimes the space is very tight. The supply duct is right in there along with the return duct. This is what happened to us with our Brookline ice dam insulation project. 


IMG_5135Supply and Return Ducts right up against the roof


Once the access was cut through the drywall, we noticed that the space was way too tight for us to make anything happen through the wall. In addition to this, the exterior wall batt insulation had been installed between the ducts and the HVAC ducts by the previous local insulation contractor. This was a major concern for us as well. We had to get a bit creative. 


IMG_5127Chase the ducts and chase the roof line to solve ice dam problems...


We had to go into the floor below the top level floor and continue our work there. Sometimes we recommend rerouting your ducts and relocating those ducts somewhere else if possible. These are all very important decisions to make in resolving ice dam issues and ice dam related problems.


IMG_5121Bring the Ducts into the home...


THE SOLUTION to Ice Dams in this case IS TO BRING THE Ducts INSIDE THE Building Envelope. This is the ideal situation that we strive for. Our home insulation project managers work with you to learn all about your duct work and hvac system and then work backwards to solve your ice dams issues. 




Ensuring that no heat loss occurs to the roof causing ice dam problems is the best thing for Massachusetts homes.


Once you have the roof well insulated now and ice dam problems have been solved, its smart to remove some of the old insulation as well and dispose it off for a multitude of reasons that we will discuss in another article. 


IMG_5122The attic kneewall before insulation removal from the Brookline, MA home...



Lath plaster wall of the attic in this old Brookline home after insulation removal...


Are you a Massachusetts homeowner that is tired of ice dam problems? Is your home like this Brookline home? We'd love to help. Please fill out our contact us form here.

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