The pex radiant heat provides about 30 BTU per foot, compared to about 600 BTU for baseboard. So, the pex is strung in a pattern to provide the same heat you know now.

I'm not sure what you mean with the other considerations about outside temperature, sunny/cloudy.

If I could do it over, I'd use under-the-floor radiant anyday over my baseboards. I think many people would. Be sure to use the oxygen barrier, heat pex.

Temperature doesn't change all that fast, so I don't know why the gas stove was suggested. If it can be heated with baseboard, it can be heated with pex radiant.

Or, are you not talking about this option?

baymee: We are looking at hydronic radiant flooring heat. Sorry I wasn't clear about that.

About the sunny/cloudy thing: We get tremendous passive solar heat (I think that's the term) from the sun because of a wall of windows on the south. On a sunny, 50-degree day it is easily 78 degrees in the living room without any heat on. On a cloudy day it will be just above 50-degrees in the living room. So, since the boiler would use an outside thermostat to control the temperature of the water, I would get the same heating from the boiler on a sunny day as on a cloudy day. We'd bake on a sunny day (I'd be opening windows) and waste fuel. Hope that's clearer now.

The reason the gas stove was suggested was exactly because the temperature doesn't change all that fast, we were told. In that sunny/cloudy scenario, if the day starts off sunny but then turns cloudy, the temperature in the living room will drop quickly. We were worried that hours later we'd still be waiting to feel warm.

Thanks for the advice about oxygen barrier heat pex. Will look up what that is.

So, did you NOT do radiant?

We built over 30 years ago when pex was unheard of, although it's been available since the '60s. I would not retro now, but those who have it, love it.

The outdoor tstat is a recent entry to our local area, but it's always used with an indoor tstat. Depending on your floorplan, you can use zones in your house and separate tstats inside. If the living room reached temp, no heat would go to that zone, but in another part of the house, there would be heat.

infloor radiant heat is not responsive like baseboard hot water heat. the reason is because the pex is usually encased in a material that does not quickly respond to heat. the same qualities that make it hold a steady temperature make it respond less quickly.

Thanks very much for responding. This is such a crucial issue for us in the design of our remodel/addition. The design of all the rooms and the heating system (even the type fuel) is based on the answer to this one question.

I've spoken with one radiant flooring owner who said we would need a gas stove for quick response, but he owns the gas stove manufacturing company. And I've spoken with one heating pro who installs a lot of radiant heat; he said he thought he might be able to design it so I wouldn't need a gas stove, but I know he knows that's what I want to hear. I'd rather not design it wrong and be miserable 'til death us do part.

Again, thanks for the help.

As stated above, if it's put into concrete, it may respond slowly, but also consider that concrete will hold its heat, so once the slab is heated and the room temperature met, you will have consistant heat. If the weather changes drastically, which is not too common and the windows aren't open, I don't see any problem.

baymee: no concrete involved. basement & crawlspace. subfloor in place. will apply radiant above subfloor & beneath finished (wood) floor.

I'm hoping to meet up with someone who actually uses radiant heat in a volatile climate. Since we are not building from scratch, there is a limit to the amount we can insulate, so that is a factor too.

Right now it is 48 degrees out and I've had to open a window because it climbed to 80 degrees in the living room from solar radiation. If it were to turn cloudy, it would drop to @55 degrees very quickly -- hopefully less quickly when we add insulation. I'm turning forced hot water system on and off several times during the day when it's sunny out.

Lot's of people use it in PA as the only source of heat. We have tons of solar gain during the day, at work. The boiler doesn't run for most of the day. But at night it works all night.

A thermostat is a stupid device. It knows that the room is supposed to be 70 degrees. If the sun comes out and the solar gain brings up the room to 71, it decides not to work. When the sun goes away, it becomes cold and starts working. That's all it is, a simple switch.

You need a combination of A/C and heat, but I don't see why you need a backup heat source.

You may also have a problem because of where the thermostat is located.

bymee: I hope you're right and we won't need a backup system; that would be ideal. I guess we'll have to install insulation and new windows and get a heating contractor to give us his/her best guess. Fingers crossed.

what you've indicated is that you do NOT have an indoor thermostat for your system, only an outside temperature sensor. Is this correct?

weedmeister: We don't have a radiant floor heating system now. Right now we have forced hot water registers (thermostat in living room). But since we are tearing down half the house and replacing the flooring, we thought the radiant floor system would be a good choice, especially in that the house will be tiny and we need all the wall space we can get for cabinets (storage). But because New England weather is so changeable and our home receives a lot of passive solar heat, we are concerned about having to wait hours while the radiant floor system catches up -- even with 3 thermostats. If we need a backup system, it will change the interior design -- to find room for a gas stove -- and might change the fuel from oil to gas.

I have radiant heat in my addition, forced hot air in the rest of my home. I live in central NJ and you are invited to see hot it works if you would like to come to my home.

Yes, it does not respond quickly to temperature changes, thatÂs true, but the pluses make it worth it. I have it in a guest bedroom that is in a "slab on grade", that means a cement slab floor. On the coldest days, that room feels great! There is no sound of hot air blowing around. The air doesnÂt dry out your skin and nose. If the door opens and cold air rushes in, it remains warm. It just feels really nice. I have it in my bathroom. When I redid my bathroom and added stone floors, the room looked good but, was unpleasant to be in. When I added the radiant in the addition, I ran it in my bathroom too. I ran a lot of extra in the shower. It feels beautiful! I ran it under wood floors in my kitchen addition and it doesnÂt work very well there. The company said itÂs about 20% less efficient under wood floors, thatÂs not been my experience.

I dealt with radiant tec in Vermont and they were very easy to work with. I dealt with David and I can really recommend him. I had a handyman install it after I figured out what I need done. The company helped a lot with the design. If anyone is thinking of doing it themselves, hereÂs what I recommend. I went through a lot of trouble trying to make a continuous run with the tubing from the water heater, to the whole room, and back to the water heater. That was very hard. Where I couldnÂt do it, my plumber made " joints". If I had known that I could have him do that from the beginning, it would have been so much easier. I thought the joints would be a problem. They are not. You do have to get a plumber to do parts of it, unless you know how to do that type of thing. The part where it was installed in the slab, I did myself. That was EASY. (IÂm a small, middle-aged woman.)

As far as the thermostat goes, you can install it anywhere you like. It will read the temperature of where ever you put it.

I got creative when installing it under my shower. There is a step up to my shower so there was a space under my shower, (this was not new construction). When I put it in the floor under the shower, the pocket of air under the shower, insulated it from the tubing and the shower was staying cold. HereÂs what I did. I opened the wall next to it. And made three "u" shaped runs of copper pipe and inserted them to the space below the shower. My stone shower feels like heaven on a cold day. It would be too expensive to do whole rooms in copper but it didnÂt run too much to do the shower. ItÂs well worth it!