Q. I need to replace my gas furnace. Are there specific questions I should be asking when I get estimates? I would appreciate any direction you might give me.
PAT VREELAND, Chatham
A. I came up with seven questions to get the conversation started as you vet contractors.
1. What size unit are they are planning on using, and how did they figure out the size? Over or undersizing will make your system work harder to keep you comfortable and could significantly shorten the life of your unit.
2. Which manufacturers do you use, and which one of those do you think is best? No one manufacturer offers solutions that meet every need. Be wary of companies that carry only one manufacturer.
3. What is and, more important, what isn’t included in the quote? Be aware that one of the biggest differences in quotes (and what is often not stated) is whether or not all the old components will be replaced with the installation of the new equipment, including fittings, pipes, valves, connectors, dampers, safety switches.
The quote provided should state, in detail, everything needed to complete the installation. This means permits from your city, removing the old equipment from your property, and all the parts and labor to complete the installation and replace old components.
4. What do your guarantees cover?
5. Is your company licensed and insured.
6. Do you take out permits?
7. What happens after the installation? Once a system has been installed, proper maintenance is the key to keeping it running.
Q. I recall a question a couple of weeks ago about window films that can be used in a stairwell where tempered glass is required (“Step-by-step instructions for removing window film,’’ Jan. 29). I replaced a window at the bottom of a short stairwell. At the time it never dawned on me to use tempered glass. To replace just the sashes is rather expensive; it seems the films might be a cost-effective alternative. Can you give me some more information on this product? Is it something a DIYer can undertake, or is it only professionally installed?
A. The safety film is called 3M Scotchshield Safety & Security Window Films, Ultra Series. This film makes windows harder to penetrate and helps hold glass fragments together after impact from break-ins, natural disasters, and the occasional lacrosse ball. Been there, done that!
The 3M film mitigates hazards from shattered glass through its micro-layered and tear-resistant properties. It also maintains a high level of optical clarity. Yes, a DIYer can do it — but very carefully.
Several readers wrote in with possible causes and solutions for the reader whose AM radios transmitted static every time the thermostat was turned up to 70 degrees (“How to repair a peeling ceiling,’’ March 12):
Rob, you are right on with your diagnosis as the cause of static on an AM radio. It is most likely radio interference (RFI). The easiest way to find the cause of RFI is to walk around the house with a portable AM radio and find out where the static is the strongest, and then shut off that source. LED light bulbs and fluorescent lamps are common sources of RFI. If you don’t find a strong source in the house, try outside. Go to the nearest light pole. Utilities have switched over to LED lights, and some radiate a lot of RFI. The wire to the house from the light pole acts like an antenna and brings the RFI into the house. If you complain to the utility company, it might come out and change the light bulb.
I am a ham radio operator and had an RFI problem with the street lamp. The utility replaced the lamp, and the RFI went away. Also, the fluorescent lamps in my attic are very close to my outdoor antenna. I need to have them turned off when I use my radios.
DICK WIKLUND, K1MGH, North Falmouth
I saw a similar issue when a new fluorescent light was installed; it interfered with the furnace! The solution? We moved the furnace’s circuit breaker to the opposite side of the panel.
JACK BURKHARDT, New England Institute of HVAC
The cause, it occurs to me, are the sparks being thrown by the carbon brushes on the commutator of the burner’s motor. If one were able to open the motor, you’d see those sparks. In a similar vein, when my old ’78 Land Cruiser still had its original AM radio, I had to buy special “resistor’’ spark plugs, which limited the interference.
Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to email@example.com or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.