Is the underfloor radiant heat viable in my case?


Hi,
I'm considering converting two of my hot water radiators to an underfloor heating system. A friend of mine, who is marginally more knowledgeable than me when it comes to radiant heating, alerted me that depending on volume of flow or rate of flow or the length of piping or some other such thing, it just might not be viable. The argument is that if the pvc piping is too long, the drag might prevent the water from circulating well.
Here's a picture of what I currently have, kind of:
http://freeboundaries.com/tight.jpg
On the left and on the right, you are seeing two pipes (galvanized?, 3"?) that go to the radiators. You can see smaller pipes (3/4", I'm pretty sure) branching off and traveling to the actual radiators that I would like to remove. Further down, they are connected to copper pipes that go into the radiators.
I'm not sure if this information is at all useful, but if it is, please tell me what you think about the viability of underfloor heating in this case.
Many thanks in advance,
Aaron
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If the sun shines in the room, you can find the room gets very hot, with the suns heat and the remaining heat in the floor. Go for a light weight floor, plywood is good, room will heat quicker and cool quicker. If your existing circulator/pump is set medium or low, then (provided the floor area isn't too big) the pump will probably manage. If the room is large, then adding another pump to help the water through the new pipe is easy. (Or you can swap to a more powerful pump) Perry
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Anything is possible, but there is more to it than just ripping out the radiators and replacing them with plastic pipe. Your house was set up and balanced for radiators. You can not mix different types of heating on the same boiler loop. This is due to the fact that different materials heat up and cool down at different rates and it will be impossible to balance. If you want to do this, you will need to repipe and seperate the system into different zones with seperate thermostats to control them. With the large steel piping that you have, that won't be easy. Good luck.

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You need a pro to run btu numbers and draw up a set up, radiant heat might run at 110f while at the same time on a cold day the radiators might go to 180f. Its done all the time but it has to be done right.
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Hi,
What does it mean that the system is balanced? My system does not have any valves except at some of the radiators and each of those is constantly turned off and then back on depending on whether the room is being used. Am I not supposed to do that? Or does balancing mean that pipe sizes were chosen intelligently some time ago?
Thanks again,
Aaron
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With most simple systems, there is but one thermostat, usually placed in the living room, used to control the heating of the whole home. Because of the limitations presented by this type of system, other, better ways have been developed.
The simple one thermostat system, uses a simple valve at one end of each radiator to limit the amount of water going through the radiator, and thereby the radiators heat output. This shares the heat available between the radiators that are turned on at the time. This means that when the thermostat has reached its set temperature, the whole system shuts down and other rooms can become uncomfortably cold.
A better way is to have thermostatic valves on each radiator, these set the temperature for each room and when that temperature is reached they turn off, this stops the rooms from becoming too hot, but it doesn't stop them from becoming cold when the single controlling thermostat turns off.
The best way! Each room has its own thermostat with direct control to the boiler. This system, called "Zoned" keeps each room withing half of a degree of its set temperature. This is the most economic system to run and it saves a lot of money. However, it does cost extra to install. And yes, existing systems can be altered to suit.
I have my home "Zoned" but with two mobile thermostats, one for the living rooms, one for the bedrooms. Bathrooms and toilets are joined to both Zones so they stay warm. As we move from room to room we take the relevant thermostat with us. I think that this way we get the best result with the best cost. Perry
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Hi,
Thanks for the very useful information!
So does this mean that my heating system is unbalanced and I should re- balance it? Also, what's the right trade to contact for a feasibility calculation - HVAC?
Many thanks in advance!
Aaron
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An interesting point, from the sound of it, it cannot be balanced, because some of the radiators do not have the requisite valves.
While I am interested in supply pipe size, because the larger the pipe size the more metal and water in the pipe, the more it costs to heat and the more money you waste when you turn it off! Most people, seem to select pipes on the basis of whats on sale today. So, a system does not need to be balanced, as in fact, you sort it out on a day to day basis ,as you feel hot or cold. If you are happy with the system as it is? Then you will be wise to let it be.
However, adding underfloor heating, will change the flow of water. Water always takes the easy route back to the pump. So, the added flow resistance in the underfloor heating, may, and probably will, mean that it will not produce the heat required to keep the rooms warm. Hence the need for either a stronger circulator/pump, or turning the existing pump to full pressure, or adding another pump to boost the flow through the floor.
Adding a normal radiator, thermostatic valve to the underfloor heating pipe, where it comes out of the floor, will provide all the control you can get, with your existing system.
If the existing radiators have kept the rooms comfortable, then under floor heating that puts out the same amount of heat will do the trick. Look up the radiator size on the net this will give you the Btu, then fit the required length of pipe with the same or larger output.
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Hi,
Here's a picture of radiator that I've been talking about that I've been wanting to remove and replace with underfloor heating.
http://freeboundaries.com/radiator.jpg
I would also like to say this: I don't really mind doing something that's wrong and then redoing it. HVAC and plumbers in my area want $1200 per person a day so whatever funds I pore into this will be nothing compared to having someone else come out and do it right. Plus I'll learn a lot.
So my plan is this. I would like to determine the BTU of this unit (can you help?) , cut it out, install PEX tubing at, let's say, double the BTU output and put a valve on it that will allow me to control the amount of heat. If this throws the whole system off balance, I will shut it off and and use a space heater until I figure out how to do it right. We are talking about an area that is about 60 sq ft.
What do you think?
Thanks a lot in advance,
Aaron
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