How to save on heating expense — a handyman project

A 50-year old two-story home in New Jersey with forced hot air has expensive heating bills in winter



This handyman project explores ways to reduce heating expense for a two-story house, with an attic, with forced hot air. Alternative strategies are outlined. This article is public domain — please feel free to copy text and diagrams without attribution. — tom sulcer November 19, 2011

January gas bills of $500+ per month prompted a New Jersey homeowner to explore ways to cut costs. Sealing cracks in the space between the door and the surrounding rectangular frame using foam with a sticky backing was done. There was a crack beneath the exterior door and the floor — about a quarter inch — which was filled by installing a wood riser piece (sanded to fit) as well as putting in a rubber door “sweep”. Exterior windows will be caulked. And insulating the attic is an obvious option.

It might be a good idea to consider hiring an energy auditor to make an inspection, and who plugs in data (including pictures from heat-sensitive cameras) into a sophisticated computer model.  These expert systems are further empowered with information collected from tens of thousands of similar homes, and bolstered with information such as fuel consumption statistics. The results can be a fairly accurate and revealing picture of which possible actions would bring the most bang for the buck.

Still, I am puzzled by the relatively high heating bills, and my sense is that weatherstripping and caulking will help somewhat but that will not lower my client’s heating bills enough. What gets me thinking is remembering what I saw in the attic — vent ducts which carry hot air to second floor rooms (which have grills in the ceiling.) Funny, but this is one of the few houses where I saw hot air ducts in the attic — why there? So it gets me to thinking.

See, here is what a two-story house with attic would probably look like, if built today. The blue box is the heater which takes in somewhat cooler basement air, warms it, and sends it through the house via gray ducts.

And here is what the homeowner’s house looks like. Heating ducts are routed through the attic. It’s somewhat more complicated, since there’s an addition to the house perpendicular to the main house which does not have an attic (which is not shown in the diagram). But the diagram represents a basic picture of the main structure. The gray is the ducts carrying hot air to different rooms. What I’m suspecting is that the uninsulated attic with uninsulated ducts seems to be where much of the heat escapes.

And why were the ducts to second floor rooms routed through the attic? Seems like a roundabout way for heat to travel. My guess is the house was built before forced hot air ducts became prominent, and a previous homeowner converted to a hot air heating system. It is easy to carry heat to first floor rooms since ducts can be routed through the basement. But installing less-than-pretty rectangular ducts through the first floor, to warm second floor rooms, was less than an ideal aesthetic solution. Apparently, then, heating was routed through the attic for aesthetic reasons, and energy efficiency at the time was less important than beauty. Such is my guess.

Wouldn’t there be significant heat loss in that uninsulated attic, with heat radiating away from the thin ducts into the cold attic air, and cold radiating back into the ducts? (see the previous diagram with red arrows representing heat loss and blue arrows representing cold chilling the attic ducts.) According to thermodynamics, energy seeks an equilibrium point between the warm air and the cold attic air.

So, let’s consider possible solutions.

Here’s one possible solution. I remember reading somewhere that the attic floor (1) is the best way to insulate an attic overall. There are two ways to do it — beneath the attic’s floorboards (requires removing them temporarily, inserting insulation, putting them back). Another way is simply to put insulation on top of the attic boards — this can work if the homeowner does not plan to use the attic space for storage.

We can insulate attic walls (2) as well, but we will need to keep a space between the exterior roof wood and the insulation (X). It adds a step but it’s worth it, since it means that moisture can exit the roof through the spaces. (If moisture is trapped, and then freezes, it can crack the wood and lead to more problems — the general idea is that houses should breathe.)

The benefit of the solution above, that is, insulating attic floor (1) and walls (2) is that the attic will be much warmer, and that heat from the ducts will not be lost as quickly as before. This could provide substantial savings, in my view.

But then what about possibly insulating the ducts (3) themselves? At present the attic ducts (shown in gray in the diagram) are the thin silver kind with folds (making for easy installation) — similar to the gray dryer exhaust ducts which collapse and expand — but much wider of course. But they would not be strong enough to support insulation wrapped around them. So, what are the options? Possibly replacing the folding ducts with strong metal ducts (like one sees in the ceilings of some upscale restaurants, which are painted) which are rectangular and would support the weight of insulation around them. Or, possibly replacing the folding ducts with insulated ducts. Or, building some kind of lightweight supports to surround the existing ducts which allow insulation to be placed around it to keep the air in. These steps might be more labor-intensive but in the long run might be well worth it.

But the plot thickens. Inside the attic, I turn the camera around and shoot several shots.

Here’s looking forward. You can see the ducts looking like laundry exhaust tubes leading through the attic down to second floor ceiling vents.

Turning the camera around, there’s this creature. Is it a monster from Star Wars? A sea creature? I think it’s a furnace — an attic furnace. First time I’ve seen one. What’s key is how thick those silver ducts are — are they insulated?

I see signs of insulation between the attic floor and the second floor ceiling sheetrock (it’s a cavity usually about a foot deep). It’s the pink stuff to the right of the silver foil. If the attic floor is insulated, then that is not the problem.

So at this point, the question becomes: is it worth it to try to insulate the attic walls? And how thick are the silver ducts? And are there any leaks? These are things to keep in mind on the next inspection of the attic.

And what other ways are there to improve heating efficiency?

One possibility is to steer heat to the rooms where warmth is key. Rooms which are unused, or used less often, can be kept cooler by closing the air vents.

Checking attic ducts for leaks (5) would be good too. They’re usually easy to fix.

The vertical crawlspace leading to the attic can have an insulated trap door installed.

Or, a removable shelf can be installed with insulation added above it.

Another thing to check: has the filter(s) been replaced regularly? Many hot air systems have filters to keep out dust and other air particles, either for each vent, or a big one in the basement, or a combination. They need to be cleaned or replaced regularly.

One last possibility. I am assuming that incoming air comes from the basement, but it may be the case that incoming air comes from the outside. If so, this will lower the energy efficiency. It is one more thing to check.

Most likely, a combination of the above methods will work.

Here are a few other projects I’ve done recently with write-ups and pictures: