Of course the least expensive to operate is the proper sized unit. Make sure they do a heat loss. Do not let them size off the old furnace. This is improper sizing. You have many more options with a boiler. It will give you more hot water than you have now but, that would mean buying an indirect water heater to add to the boiler which could be done later when your fails. The operation cost for heat would be about the same but when the hot water tank is added it would be a lot less expensive than your present water heater. DO NOT USE AN INTERNAL COIL IN THE BOILER! Too expensive. See link. http://www.comfort-calc.net/Domestic_Hot_Water%20_Coil.html

Chisue, I'd say 4K is probably not a bad bid. It is more expensive to retrofit than to install originally and it isn't quite as simple as just running some pipe under your existing floor. I don't see that the value of a 5K home in your neighborhood has much of impact on the conversation. From experience, the cost difference in many home retrofits and repairs in a high value RE value area, in the range you mention, and another in a low cost area, is not that much except when transportation costs of materials is at issue. In fact some services and inputs are more expensive in our lower home value area than in our higher value area, simply because more local trades that do higher end type installs are available and competing for work. From our experience we have to often hire someone from the nearby city --45 miles away -- to do the work and that does come at an up charge, understandably. There is also the fact that smaller jobs also cost proportionately more than larger jobs anywhere. It might help if you don't put down the trades as simpletons. If don't like the bid or can't afford that price, why don't you just go hire someone off the streets to install the tubing, direct the job yourself and just ask a master plumber to make a call to hook it up. LOL. Be sure to pull the correct building permit if ine is required -- it often is for additions to mechanical and plumbing systems.

Sounds like you live in one of those rare climates where radiant floor heating makes sense financially. It is one of the most efficient ways to heat but as live wire points out, if you are including any type of AC or heat pump for cooling, then the upgrade to radiant is probably more of a luxury add-on whose cost effectiveness is very much in question. Sounds like forced-air is still cheaper overall than radiant in your area. Radiant floor heating is less comfortable than forced-air for homes that meet international code levels of thermal performance. If you can feel the heat of a radiant floor by touch, it suggests the building envelope was not proven airtight with a blower door test and probably does not have adequate levels of insulation and fenestration performance. Thermostat response delay or lag time is the reason forced-air is arguably more comfortable than radiant. Outdoor temperature, mood, state-of-rest and other occupant dynamics benefit from quick thermostat response. Radiant floors respond slowly to changes in thermostat. Don't base your experiences of forced-air heating on older, inefficient homes. A home built to international code minimum performance has very low CFM (airflow) requirements. A professionally designed and installed forced-air system results in operation that is barely noticeable. Hire a third party certifier, like energystar to verify your home is designed to meet international code minimums and upgrade to have a Manual J calculation by this third party certifier. The nice thing about energystar is that an outside party will be verifying your home is built to minimum standards and that the HVAC system is installed appropriately. It's also important to choose a builder who is comfortable with this process of checks and balance. It sounds like healthy Indoor Air Quality IAQ is important to your goals as it should be. I would argue that forced-air can be better for dust control because it offers the opportunity to use filters to capture dust in your indoor-air, dust that is present whether you have radiant or not. Most people's problems result from poor construction protection and not having filters at return grills. Filters can reduce dust but should not be the primary strategy for IAQ. Outdoor-air ventilation is the best way of ensuring healthy indoor-air and most systems rely on some amount of ductwork. Using a third party certifier is a great way to ensure these systems are installed and commissioned in an appropriate manner, as most programs are following ASHRAE 62.2 minimum ventilation rates. Eliminating attached garages, vented crawlspaces and indoor combustion appliances are more important for indoor-air quality than any concerns of radiant vs forced-air.

Thank you rweigand - I will check and also try to get some photos of the setup. The filter was replaced just a few days ago. Do you reckon having humidity meters on each floor is a good idea? PS: We're in Massachusetts. The weather has been all over the place in recent days. Its rainy and 11C today and tomorrow, and then dry and 21C on Thursday! Hows that for xmas eve? Never thought I'd see that kind of temperature for xmas! mike_home - There is no doubt we have air leakage issues. We have drafty windows (and it is a very old house anyway) that will be replaced in the 2nd week of January and then insulation will be blown in to the external walls on 19-20th of January by a MassSave contractor. Should we wait it out to see what changes the windows and insulation will bring before blaming the HVAC system for all our humidity woes?