Ice dam caused from attic installed heat exchanger?

Heating a not insulated attic in PA seems rather unusual and sounds very wasteful and expensive. I assume you have a sloping roof, right? So why not follow the conventional building practice. Put a heavy layer of insulation on your attic floor, which is the ceiling of your house. Then disconnect the attic heating and leave it at that. The insulation on the attic floor must be done well, professionally. 18 to 20 R should be sufficient to reduce the heat from the house escaping through the ceiling to a mere trickle.

The heat exchanger in the attic is for the heat pump and is the main source of heat for the house, but it does not heat the attic except for the heat loss from that unit itself.

If the heat exchanger in the attic is the source of energy to be transferred by the heat pump into the house, then this exchanger will refrigerate the attic. Something is not computing here....

If the heat pump reverses to become an air conditioner in the summer, the attic is a poor location for the condenser. Again no computey.

Sorrry about the confusion. The heat exchanger unit in the attic has the fan blower for the heat pump and also houses a electric heating coil used as an emergency type of heat that kicks on when the outside temp is too cold for the heat pump to work. My house is built on a cement slab with no basement and the heat is downdrafted from the attic which containes all of the ductwork.

My heat pump is located outside of the house. Hope the added info helps. I also have tried the heat tape on the roof a few years ago and did not work. It seemed to me that the melt, refreeze on that section of roof was too fast and too much for the heat tape to hold up to the task.

You said the ductwork is in the attic? Is the ductwork insulated? If not, it should be. Insulating the underside of the roof would probably help the ice dam problem too.

Probably most important is to get a thermal imaging camera (maybe borrow from the fire department??) and find the heat source in the attic. The compressor and fan motors should not produce that much heat, and the radiator unit will cool the attic space in heating season as stated. So I'm going to guess the ductwork is the heat source.

When I had a heat pump, the unit was outside; why was yours placed in the attic?

The heat pump is located outside, but there is a supplemental heat source located in the attic used as a emergency type of heat when it is too cold for the heat pump to run... this is an electric coil very simmilar to what a baseboard heater would do. It is not insulated and this might be the cause of the heat loss thus causing the very fast snow melt on that section of the roof above.

There you go. An uninsulated heat source in your attic. I'm certain from following this thread that this is your problem. The goal of an attic insulation and ventilation system is to not have a significant temperature difference between inside and outside, 22 degrees is too much. Now, likely this electric heat source has a rating for how much insulation can be applied to it. Verify this before packing fiberglass battings around it. The last thing you want is to create a fire hazard. I won't be to surprised if you find out that this heater is not designed for attic operation and it should not be insulated. Well meaning people have done dumb things.

You have to keep the heat from making direct contact to the underside of the roof sheathing. That is causing condensation on top of the roof that is freezing into a dam. I'm assuming that your ice daming is occuring at the eaves. In that case you need cardboard baffles between your ceiling insulation and the underside of your roof. The baffles must have an air gap of at least 2 inches to the underside of the roof sheathing to allow for the cool air to flow freely.

We're all speculating here that the dominant heat source in your attic is the heat exchanger. This may not be true. While we still have this cold weather you might consider renting an infrared camera or if your ambitious (aka cheap ) you could modify a CCD camera to perform a thermal scan of your attic space. It just might be that you were already loosing heat into your attic space. The earlier heat loss was only marginally below what would create this ice dam scenario. By adding the heat exchanger you've made your room warmer but are now melting the snow on the roof from underneath.

The only other thing that comes to my mind is how is this attic space vented? If air cannot exchange out of this space, you will certainly have snow melt problems.

I'm surprised that you would have a heat pump in PA. The setup you have is common here in Az. The majority of the system is outside and plumbed to the heat exchanger in the attic.

Maybe wrap the heat exchanger with insulation? It takes a lot of energy to raise that volume of air 20 degrees.

BTW, my heat pump has been known to run most of the night on really cold nights, and in the middle of this, it will freeze up and go in to a defrost cycle. That means that it acts like an AC unit for about 10 minutes. Oh, for gas heat.

Welcome to the club. The best think to do is crack an Iron I mean Rolling Rock maybe a Yuengling, turn on the Pitt game and try taming your mullet by rubbing GoJo in it.

A lot of the houses around here, mine included, don't have proper overhang, so you can't get a good transition zone between the insulated space and the outside. So, you always have that melt zone somewhere.

I've had to remove a window on the first floor in order to open the header and install a drip collector, and I've drilled at least a dozen holes in the subfloor to drain the water. I've also opened up a pretty good hole in the basement. And, I still have water coming in. If I had it to do over, when Julie Baloney predicted 4-8" of snow, I'd have ripped the back gutter right off the house. It would have been cheaper.

Misery loves company.

No matter how the attic gets heated, that is not the problem here. The sun would also melt the snow and create the same problem. The problem is ice damming on a less than optimum sloped roof.

I'm sure changing the slope is out of the question so attacking the snow and resulting ice is the way to go.

The hard way is to construct, or buy if it can be found, a snow rake and scrape the snow off the roof. It can be done, my elderly father insisted on doing it for years. He also used to direct a stream of hot water onto the roof. Effective but wasteful. Then he had a purpose designed, heated wire, in a triangular pattern at the lower 4' of the roof with returning wires running through the gutters and through the downspout, installed. Turn it on whenever the sun is shining or temp is over freezing. Any meltage that drains into the gutter runs out the downspout and doesn't have a chance to freeze and backup from the gutter onto the roof under the shingles. Once the sunlight moves off the roof and the temp drops, there is no more meltage and the system can be turned off. There are contractors that install these systems or they are available at home centers. Simple pipe heat tape is not sufficient.

As a roofer in upstate NY, there are several options; Install proper vent between the rafters, and insulate. Be sure to install vents in your soffit.

Another way is to install snow slides; there sheets of aluminum made for that. They cover the bottom 3 feet of the roof.

The best (and most expensive) way is to install metal roofing. The snow and ice will not stay on it long.

I think you should consider a metal roof also
I had metal installed on the back half of my old two story here in Kansas
with a steep gable type roof and now with the very bad snow storms we've had
it wakes me up at night as the snow slides off the metal roof, overshoots the gutter
and goes thud thud thud on the ground all night

But I'll get used to it and the peace of mind knowing it's not overloading my roof
and I don't allow any car parking under it either

But there's no possibilty of any ice daming or snow loading on that side of the roof
and it was cheaper than asphalt shingles but this old man won't be doing any
antenna up work there now as I can't stand up on metal without sliding off

Hi:

I have a metal roof, 45 degree slope and the snow for the most part slides off. However in the SW quarter, the rapid heat-up melting and then freezing turns the gutters into an ice jam. I believe, I will have to put in heating cable. Otherwise the gutters will rip off.

I feel that your best bet is to take some mineral wool insulation and insulate the ductwork where your electric heater is located. Where is the external heat exchanger, ie refrigerator in winter and condenser in summer located? You don't wan't to insulate these sections.

Good-luck!

This is a common problem in Canada. If heat is trapped in the attic it will melt the snow at the eaves and water will find its way down to the ceiling below.

Building codes require that the roof insulation placed on top of the ceiling must allow intake of fresh air between rafters via intermittent soffit vents placed at the eaves overhang.

If you a have vented attic as described above, ensure that the insulation does not impede air flow. There are plastic pans available at building suppliers for such situations.

Cheers

Vince

What kind of ventilation do you have in the attic? You are going to need more ventilation in the area of the heating system.

Ridge vents are great in the summer but once you get enough snow on the roof to cover the vents then air circulation stops and ice dams begin. I've been putting mushroom vents on our house because the ridge vents just don't work in snow.

You have to make sure the vents in any overhangs are working and not clogged by insulation too.

Tough to say more without seeing or getting more details about the installation. I do agree that the metal roof would solve the problem but the $$ involved will make your eyes pop in the short term.....

All of you have some really great ideas. Some I've already tried and some I haven't. A new metal roof is out as just replaced it 5 years ago with another asphalt shingle one. I strongly hope that if I insulate the enclosed heating coil, that should eliminate the problem. I was up in the attic yesterday and could feel very warm air around the heating coil and tried a thermometer test the night before and in to the morning. I kept the thermostat set at 60 degrees so the heat pump would work with out the electric coil kicking in to supplement the heat, the outside temp. had little change. The attic remained a temp. of 41 degees thru the night and early morning. I then bumped up the thermostat 2 degrees, just enough for the heating coil to turn on and in half of an hour the temp. on the thermometer rose 14 degrees. The thermometer was placed about 3 feet to the side of the heating coil enclosure. That kind of makes sense as the snow on the roof above the area has been melted now for days and as you go further away the snow is still up to my knees.

I went out today looking for some good duct wrap insulation and had a hard time finding any at all. I ended up buying Frost King brand fiberglass with foil backing and R value of 6. I hope this works... we're supposed to get another 4-8 inches of snow today. This has been the worst winter here in the 17 years of being in this house. I know I'm not alone, but when is it ever going to get warmer?

Patience. Global warming will take time

I do have ridge vents at the peak and also have vented soffit at both ends of the house. I also have baffles installed in the attic to keep the insulation off of the rafters where it meets the soffit.

There are a couple of things you can do to reduce the ice dams.

First, make sure the insulation in the attic was installed correctly and has a sufficient R-value rating for your area. If not, you can have someone blow insulation into the attice.

Second, make sure your soffit is well vented. At a minimum, there should be a vent shoot in every other rafter (ideally every one). The shoots are placed at the eve of the roof. This keeps the insulation from blocking air flow.

Third, make sure you have proper venting in the roof. Check to make sure the peak of the roof is vented across the entire roof except for the last 2 feet. You can also add powered roof fans to ensure air movement. The powered fans also help remove heat in the summer.

Fourth, make sure all of your duct work is insulated. If the duct work isn't covered by the insulation, you can add insulation to cover the duct work. This will help reduce the heat loss.

This should resolve the problems inside the attic. You can still get ice dams along the eaves due to the freezing and thawing of snow on the roof. You can also have ice dams due to ice build up in the gutters.

you could also go to wood heat. You can get wood free from most small tree services throughout the year. Crank your wood heat up so your house stays about 80f all winter. All the snow will melt off pretty quick and not dam up in your gutters. I did have one downspout freeze itself closed from the water running through it and freezing ,though this week.

All your replies are good advice.

In my experience the temperature inside the attic should be almost the same as the outside temperature. Heat loss through the roof melts the snow and the resulting water freezes on the eves, which remain cold because they overhang the attic walls. Water backs up under the shingles and leaks into the attic. So, ventilation is the key. Keep the attic cold. Insulate the floor of the attic and anything producing heat that's on it to stop heat escaping into the attic.

Radiation, conduction and convection are the three modes of heat energy transfer. I doubt the hot unit is touching the roof so it is propbably safe to rule out conduction.

Can you take a surface temperature reading of the underside of the roof deck directly over the unit and some air temperature readings in a few other areas in the attic? This can shed light on heat gain by convection. I suspect this is your culprit causing the frozen section of the roof directly over the unit.

Heat energy travels towards cold amd radiant heat is emmitted in all directions. The colder air comes in contact with the hot surface, picks up some of that heat energy and the hot air rises and is replaced witrh colder air. That convected heat energy is then transferred to the underside of the attic roof.

The key statement here is "comes in contact with the hot surface". The problem being mostly caused by the radiant or convected heat gain to the roof will be a source of debate for certain, However, the hot surface of the unit itself IS the cause and the problem that must be dealt with to lessen or stop the amount of heat gain to the air.

You need to reduce the exterior surface temperature of the unit to help your problem with radiant heat loss and that will result in less loss/transfer of that heat by convected heat .

I work with an insulating coating that has stopped problems similar to this on hot equipment and surfaces. As an example; In a hospital we coated a boiler and the steampipes in the boiler room. We reduced the surface temperature of the metals from 267F down to 155F with around a credit card thick application. This proved to be a 35% reduction in heat loss through those metal surfaces.

I am certain it would have a similar effect on your heating unit.

Send me a note to ceramatech_engineering@yahoo.com with mailing information and I will be happy to send you a cured sample on a stitchbond polyester cloth. You can lay that on the surface and take a few temp reading to see what it could do for you.

I think we are going to make your unit more energy efficient at the same time we fix your problem.

Hal Skinner

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