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:
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,
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
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.
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.
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?
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
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
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.
Thanks for the very useful information!
So does this mean that my heating system is unbalanced and I should re-
Also, what's the right trade to contact for a feasibility calculation
Many thanks in advance!
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
Here's a picture of radiator that I've been talking about that I've
been wanting to remove and replace with underfloor heating.
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,
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