Many people dislike forced-air systems (furnaces and heat pumps), because of drafts, dryness and air stratification problems. On the other hand, many people praise hydronic systems (hot water boilers-radiators-baseboards or radiant floor heating).
But in practice the difference in quality and the advantages and disadvantages of each system are much more nuanced.
Overall there isn't a huge advantage of any system, and even issues like cold drafts and dry air caused by forced-air systems are usually a symptom of other problems, involving home leaks, undersized ducts, oversized furnaces or clogged filters. Proper maintenance, high levels of home sealing and correctly sized ducts and furnaces, can solve these problems and make forced-air systems able to provide high levels of comfort.
The bottom line: there are other advantages and disadvantages that should be considered.
Our Video on Boilers vs. Furnaces:
Advantages and disadvantages
In very simple terms we can say that furnaces and heat pumps systems provide a quicker way of heating our rooms, and that their ductwork can also be used for cooling and ventilation, which doesn't happen with the pipes of hydronic systems; and also that there are less customer complaints about furnaces and heat pumps than about boilers (at least in the US), or that they are cheaper than most hydronic systems.
But hydronic heating have also some advantages: namely, they can provide very high levels of comfort, and are quieter and easier to zone (room by room heating) and less prone to heat loss.
Obviously, some of these pros and cons - the price, the heat loss, the reliability... - are variable and dependent on the exact system and installations issues.
Ducts and pipes
Ducts are more prone to leaks and heat loss than pipes. Leaks can remain undetected for long periods, but they may amount to 30% or 40% of the heat produced by the furnaces and heat pumps. Ducts require pressure, to keep heated air flowing evenly to the registers; without proper pressurization, the system will not work, but it also increases air leakage in ducts, and heat loss.
On the other hand, there is a downside in the hydronic distribution systems, already mentioned: pipes can't be used for cooling, or for ventilation, contrary to what happens with ducts.
Ducts have, after all, a positive and very important advantage too – all the more that hydronic systems are also subject to heat loss.
Installed boilers are often oversized, which greatly affects their efficiency. The more the boiler is oversized the greater the cycling losses. In other words: instead of working smoothly and responding to the heating needs, oversized boilers will restart too frequently, wasting more energy.
Be aware to sizing criteria. If a boiler is sized to meet the heating requirements of the coldest days, it may become grossly oversized in less extreme temperatures, and cases like this should be carefully considered. In many cases, it makes sense to use an auxiliary system during the coldest weather periods.
Do not underestimate this issue. Energy losses due to oversizing can be huge, and boilers should be sized according to the type of building and its insulation levels, or the type, number and size of windows, and never according to simple rules of thumb.
Slow and quick heating rates, and zoning
It’s easier to divide a house into separate heating zones (room-by-room heating) with hydronic systems than with furnaces and heat pumps. Hot water boiler systems can easily be designed with separate circulator pumps and piping.
But on the other hand, hydronic systems are slower to respond to heating needs. Rooms will take a longer time to heat up with radiators, baseboards and radiant floors. And that, in practice, can make hydronic zoning rather ineffective. Zoning strategies, to be effective, require heating and cooling systems able to respond quickly to the room occupancy – something that hydronic systems do not provide.
In other words: the zoning advantages of hydronic systems can be very illusory. Zoning with air forced systems – involving special duct dampers, and thermostats in each zone – can be more effective than zoning with hydronic systems.
On the other hand, zoning does not make much sense in modest-sized homes with high levels of insulation and sealing, and high-performance windows.