old boiler and new radiant floor heating

mike g_4

I really appreciate your thoughts and ideas. As you mentioned, i am skeptical about temp and heat it will give off.

I have thought about the electric option, because it is such a small area. It was my impression though, that the electric mats (whether installed for the floor or wall) weren't meant for continuously heating areas, but more for intermittant comfort. Thoughts?

mike g_4

old boiler, new radiant floor heating.

anybody have any advice/opinions on how to replace an old radiator and instead use radiant hydronic floor heating.

House is in southern Wisconsin, the room is a half bath on the first floor. The bathroom is getting completely redone down to the studs. I want to remove the small radiator (gain a little space, bath is only 4 x 5 ft) and still use the same boiler thats used for the rest of the house.

Is radiant floor heating, either in the subfloor or below between the joists even an option? Will i have a problem with BTU, adjusting the temp, or the install?

I am having a hard time finding info on the topic.

Any advice is helpful.

Mike T., Swampeast MO

Almost anything can be done with hydronics--for a price...

Unfortunately, a number of things will likely be working against you and what might seem a simple proposition could become extraordinarily expensive for proper comfort, control and system efficiency.

My gut reaction is to suggest electric floor heating under tile for use in the half bath. Before you remove the radiator however someone should verify that the floor alone will provide sufficient heat. Small baths often have a deficit of heatable floor area. The electric heat could easily be extended into wall(s) if necessary.

While it's sometimes possible to just "tap in" to the existing system for a floor, temperature and time are likely to be your enemies. Many heating systems with standing cast iron radiators operate at a quite low temperature--too low to be used for "underfloor" heating methods yet too high to be used for "above floor" heating methods.

Even if the existing supply temperature is suitable, the problem of time can occur. Most old systems with cast iron rads find the circulator and boiler running in unison. With their large water content, iron rads give off their heat slowly for a long time after the burner stops firing and the circulator stops moving water. Your floors will have little water content by comparison and while the temp may be suitable, it likely won't be "on" for long enough and the floor may well never get sufficiently warm.

A separate zone for the bath could be added of course, but be aware that this cannot only be quite expensive, but that it can be extraordinarily inefficient as running a boiler suitable for heating the entire house just to heat a half bath will introduce a HUGE amount of cyclic waste (especially with a conventional, cast iron boiler).

If you really want hydronic heat for the bath floor, I would suggest finding a very good hydronic heating contractor--not your average plumber.

Again though, I really suspect that electric will be your most comfortable and cost-effective method for such a small area.

Mike T., Swampeast MO

Since the conditions where they will be installed vary so greatly, most manufacturers of electric floor heating systems call them "floor warming" the implication being that they would not guarantee that they alone could heat the space.

Despite having hydronic heat available for floors, I used electric for the majority of my master bath (the shower is hydronic). It has a cast iron radiator as well (with a TRV). It is on a Northeast corner, with significant exposure and a very large glass block window. In typical weather, the electric floor heat cycles and the radiator is stone cold.

If yours is a rather typical old house downstairs half bath with short, single exterior exposure and a smallish window, I would suspect that an electric floor system would be sufficient--especially if you can nicely insulate any exterior wall. One of my baths (fully internal) is located between two bedrooms that are normally kept at about 55F. The bath floor has hydronic heat (constantly circulating) and the doors are kept closed. Despite an air temp that rarely exceeds 62F or so in the heating months and a floor temp that is generally "neutral"--only warm in quite cold weather, I find it the most comfortable "reading room" in the house during the early morning.