Which gas heat is more efficient, furnace or fireplace? It depends

Q: We have a 10-year-old home with a glass-front gas fireplace in the family room, the sort many newer homes have. It has a pilot going all year, and this summer I noticed heat outside the house emanating from the pilot light. Now that the weather is chilly, we turn on the fireplace many evenings, sometimes with or without the house furnace set to operate. The question is, which way is cheaper to heat our house, the fireplace or the furnace?

A: Nominally, a newer gas forced-air furnace (78 percent to 94 percent efficient) is almost always going to be more efficient and comfortable than a direct-venting gas fireplace (most range from 65 percent to 82 percent.). However, the fireplace can be cheaper to operate since it allows you to create "zones" if desired.

If there are rooms you can keep cooler, such as extra bedrooms, heating a portion of the home with the fireplace might slightly decrease your total utility billing. Duct losses (air leaks) in forced-air heating systems also can create surprisingly large efficiency losses you will never experience with a fireplace.

In the summer, you have absolutely no need for a running pilot light in your fireplace (the gas bill or unwanted heat it provides), so shut it off. The mere fact that you have a pilot reduces the overall efficiency of the fireplace — AFUE (Annual Fuel Utilization Efficiency) vs. steady state efficiencies) — so in the end the electronic ignition furnace comes out on top. Of course, the fireplace looks better and is a whole lot warmer when the power goes out!

This conversation was predicated on the most popularly installed type of gas fireplace, a direct-venting unit, not the type that vents through a vertical chimney or lacks a sealed combustion chamber — these are much less efficient.

A ventless fireplace is virtually 100 percent efficient, beating any kind of gas furnace hands-down. While that may sound great, ventless fireplaces have a host of other problems real and imagined, such as moisture buildup in the building.

Q: What is the proper method of painting T-111 plywood siding? Painters usually spray paint with no special effort to further coat the cut edges of the plywood exposed by the grooves. The result is that those exposed edges have very little paint protection. Yet lumbermen and home inspectors I've talked to say that after spraying, the grooves must be gone over with a brush or roller in order to get a good coat of paint on the exposed edges of the plywood. I am having some difficulty sorting this out with my contractor and would appreciate any help you can provide.

Q: I have a bet riding on your answer. We are repainting a 6-year-old building with latex paint. The siding is T-111 plywood. Does the entire building need to be primed, or just the bare areas where the paint has peeled? Does the building need to be back-brushed, or does spraying alone do an adequate job?

A: More than any other siding I can think of, T-111 absorbs paint like a sponge. Older T-111 tends to get slightly raised grain, making it even more difficult to cover. A building I own with this siding was painted professionally recently. At my direction, the contractor bid for only one coat, partly because I was too cheap to pay for two coats, and partly because we were hoping it would adequately cover with one, as the siding looked great. The west side had the most sun and rain exposure over the years, and therefore the most raised grain.

It didn't cover. Not even close. He sprayed paint heavily from all directions, left, right, up and down, until paint literally was running down the wall. I went out two days later with a roller and got the worst areas. And then I did it again. And again. Yeah, four coats on that blasted west wall!

In hindsight, it might have been easier to just remove the siding and dip it in a vat for several hours. But I'm not bitter about it. So yes, I am a big believer in back-brushing and rolling T-111, both for the raised-grain issues and to force paint into the grooves.

All bare spots need to be primed. The painted areas should not need primer.

Darrell Hay answers readers' questions. Call 206-464-8514 to record your question, or e-mail dhay@seattletimes.com. Sorry, no personal replies. More columns at www.seattletimes.com/columnists.