Radiant heating and two contractors with vastly different opinions… Is there anyone out there who can settle this? Both contractors are very smart with engineering backgrounds and many years of experience. Long story short: 89 year-old steam boiler…I need a new heating system. First floor: (sub floor 1 x 6 plank – entire level) two bedrooms and hallway have ¾” hardwood flooring covered with pad and carpet; living room and front entry ¾” hardwood flooring; dining room ¾” hardwood flooring and linoleum; kitchen and bathroom have 1” cement mud and ceramic tile. Second floor: two bedrooms and master bath are getting radiators, no radiant heat. One more twist: In the next two to three years we plan to tear out the carpet and linoleum and recover the entire first floor (except the kitchen and bathroom), over the existing hardwood and sub floor, with ½” engineered hardwood flooring. Contractor number one says that I need to go with a water boiler system instead of a geothermal system because the hardwood floors and carpet are insulators and the geothermal system does not put out enough heat. Contractor number two says the thicker the flooring the better. Carpet, wood, the more wood the better, more insulators means better thermal mass and geothermal heat is perfect for my application. Which contractor is right?

I have no idea if the amount of flooring is a problem for you specifically with geo because I don't know your heat load or radiant application method. So what I'm about to say does not mean that geo radiant will not work in your house (though I do have to note that it's unlikely without supplemental heat, or very low heat loads).

Neither of them know for sure without doing heat load calculations either, I should note, and if neither one is, you need to find a new contractor. Especially if you're going to drop the dime on geo, you need to drop it with someone who is running the numbers.

that said, the fellow claiming all the insulators are "thermal mass" is totally wrong.

NRT.Rob, Thank you for your reply. Both contractors are doing heat load calculations. Contractor one came up with heat/60,000 Btuh and cooling 42,000 Btuh. So supplemental heating is required. Both guys would be using PEX tubing under floor between the floor joists for the first level and radiators for the second level.

The heat loss calc has to be done on a room by room basis to be able to know how much of the heat load for that room/zone can be supplied by radiant, and at what temperature, since some rooms are far lossier per square foot of floor area than others. A heat load of 60K isn't terrible if it's distributed over 3000ft^2 of exposed wood floor or greater, but it's quite the challenge (or impossible) to get that much heat out out of 1200' of wood floor without either frying your feet on it or compromising the wood with higher (higher than efficient geo) water temps.

The "more wood is better" theory based on thermal mass only works if the radiant is installed above the subfloor to be able to work at the lowest possible temp. If it's a staple-up, thinner stackups get more heat into the room at any given temperature. Carpet & pads tend to be more insulating than wood and has minimal thermal mass and generally to be avoided if you're trying to keep water temps low, and/or maximise the fraction of the load carried by the radiant. Mayhaps he meant "more wood than carpet" as finish flooring(?).

Wood is far more insulating than (and doesn't have nearly thermal mass as equivalent volumes of) concrete & ceramic, but if the radiant is installed under the upper layers as opposed to below the sub floor it doesn't hurt to have thicker wood below, and it's operating temp can be low. Higher insulation value is by no means an indicator of higher thermal mass- it's usually quite the contrary, but they are for the most part independent aspects of a material. If it's truly the contractor's position that putting more wood & carpet between the tubing and the room the system is a performance enhancement due to the thermal mass, lose their phone number- they haven't a clue!

It's sometimes easier/cheaper to run radiant ceiling than radiant floor, which has the advantage of more unobstructed surface area, but if you're living there at the time, demoing/replacing the ceilings is pretty messy compared to retrofitting staple-up radiant on first-floor only working from an unfinished basement.

Dana1, thank you for your reply. my house is 2400 sq ft so if the floors were all wood/tile it sounds like you agree geo radiant floor heat could work? (both contractors did a room by room analysis.) but it sounds like it is not recommended to use geo radiate floor heat for rooms with carpet, is that correct? is it okay to use radiant floor heat in carpeted rooms if using a water boiler with higher water temperatures is employed instead of geo?

technically you might make geo work under carpet too. however, carpet is a red flag with a low temp method like geothermal to "tread carefully" and, in MANY BUT NOT ALL cases, you'll need a radiator, loop of radiant ceiling, or some other form of supplemental heat in carpet areas with geo.

Geo CAN work in any case. whether it will or not depends on the contractor, your heat load, floor coverings, and install method for the tubing.

I would like to also add that may seem tempting to satisfy the 60,000 heat load with a 5 ton GSHP. Don't short yourself. Geo is one of those systems where slightly bigger is better, especially on the earth side. Then have a buffer tank on the waterside. Along with the other advice given, only then gshp may work.