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Radiant heating

We are in the planning stage of renovating a bathroom. We currently have forced hot water heating and are looking into changing to radiant heating. We are trying to avoid electric radiant heat do to the high cost of electricity here in New Hampshire and was wondering whether or not is is worthwhile to install hydronic radiant heating under our new flooring. We may consider doing this in another room in the near future as well.

Jay Wulfson

Re: Radiant heating


I would say YES---since the bathroom usually has a small footprint, it's an ideal choice for most people who want to get into radiant heat---walking barefooted on warm bathroom floors is something to experience.

For someone trying to get started into hydronic radiant floor heat, it's a good strategy to start with a small area,such as the bathroom, hone one's radiant installation skills, iron the bugs out over a year or so, then expand one's experience into the rest of the house, if desired.

These are hybrid systems, where for the time being, the rest of the house remains on 180 degree hot water heat & a 3-way or 4-way mixing valve (see TOH site below & diagrams by Harry Campbell) is used to produce 120 degree water via manifolds that runs thru PEX (plastic) tubing that is installed under the bathroom floorboards, or on the bottom part of the flooring (staple-up) between the floor joists, if there is access to do this type of install--click onto the Harry Campbell icon to get all 4 diagrams showing the manifolds & other radiant components.

Could you advise on the square footage of the bathroom & the ceiling height.

Google "radiant floor heat" or "radiant floor heat forums" or "installing radiant floor heat" to get additional relevant sites.

There are numerous sites on the web that deal with this project (some below), but try to hook up with a forum that specializes in hydronic radiant heating, so that you have a "back and forth" dialogue with experienced installers.

A good forum to start with is with heating help---click onto "Ask Questions" when you get to the site, & then click onto the forum that specializes in "Radiant Heating"

The house needs site below starts you at initial steps like calculating a heat loss estimate of how many btu's/hour the bathroom needs, according to its square footage, and then planning the amount of plastic PEX tubing that has to be installed.

Google "A Little Floor Warming Please" by heating engineer John Siegenthaler, who has piping diagrams with the article that explain how this type of project is done---some public libraries carry his book "Modern Hydronic Heating", which is very readable & loaded with info.

There happen to exist a number of radiant floor companies in Vt. that sell radiant floor kits & offer free brochures on their installations & products---the radiant company site listed below is one of these---I don't recommend or have a relationship with any of these companies, but they do offer free installation manuals & won't bug you with literature or e-mails, or try to sell you something---they seem to favor using a high-priced HW heater as the heat source, while I favor using a 3-way or 4-way mixing valve attached to the boiler, or even extending the 180 degree distribution lines of the existing heating system to avoid adding a lot of expensive components (see latter part of Siegenthaler article).

A related strategy is to set up a separate 180 degree zone for the bathroom area using sub-floor staple-up PEX controlled by a 571 series Taco zone valve with its own thermostat, which would control the heat level for the bathroom area.

Your first impulse should be to go with Siegenthaler, Dan Holohan (heating help) and Richard Trethewey (TOH)--Google each one of their names combined with "radiant floor heat" or "installing radiant floor heat" & see what comes up.


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