Can you insulate old plaster walls?

[Charles]

My home was built in 1944, and even the new addition, a porch converted to a dining area about 20 years ago, has lath and plaster walls. Is there a way to insulate these walls?

Also, would it be practical to reinstall oil heat? We now have a heat pump - we bought into the "it's not your old heat pump, it will save money over oil" sales spiel.

[home improvement guy]

It appears there are two very different questions here on the same topic - energy efficiency - and I'll try to answer each.

It is possible to insulate lath and plaster walls. Many homeowners do this as part of remodeling projects, since the walls have to be ripped into anyway. I assume that is not part of your overall plan, however.

Some old-house experts have told me over the years that thick plaster walls and the wood lath underneath are thicker than most drywall. These walls were designed to breathe, meaning that they provide more than enough ventilation to prevent growth of mold.

I don't subscribe to this; I'm just sharing.

Two of the houses I have owned had plaster walls, and I tried to seal gaps where the walls met the floors and the roof, to reduce air intrusion. In the house that had an attic, I insulated the floor there. But my efforts didn't seem to make either house more energy-efficient.

The method I've seen most often is blowing cellulose insulation into a hole punched into the plaster wall. This has to be done very carefully, so the insulation is evenly distributed and doesn't settle in one place.
Obviously, it's difficult seeing behind the walls when this is done, but qualified and experienced insulation contractors are very good at it.

At the website www.urbanpatch.org , I found a great video series that demonstrates the technique. Look for a link to the "Delaware Project."

Heat pump versus oil? Add natural gas to this question. Each has its merits and negatives. Research is the key to success, and you need to do your homework.

Don't skimp on price. The most energy-efficient option is the only way to go, even if it is the most expensive.