We have difficulties getting enough heat.Ten years ago, when the
furnace was installed everything was ok. Now when we set the
thermostst to 66 degrees F the house heats up only to 62 on cold days,
and if I open more radiators, the temperature in the rooms which were
heated originally drops. The gas and electric co., with whom we have a
contract, did help somewhat several years ago but was unable to help
last year.

I suspect that the heating pipes are getting clogged with calcium
sulfate eposits(CaSO4). From my chemistry I know that Na2CO3 (washing
soda) will convert calcium sulfate to calcium carbonate, at least in
the laboratory, and the sulfate ion will get bound to the sodium. If
adding sodium carbonate to the heating system will do the same - then
I could let out the soluble sodium sulfate with the water in the
heating system, add tap water, do this several times untill all the
sulfate is gone; Subsequently the insoluble calcium carbonate now
clogging the system could be dissolved in tap water to which vinegar
is added. Has anybody done such a procedure? Was it successful? Or was
the problem worsened by the calcium carbonate formed clogging the
system worse or by the vinegar making holes in the radiators or the
steel pipes?

Does anybody have other suggestions except tearing the walls and
replacing the pipes?

This reminds me of a joke. The question was: will hydrochoric acid
remove the scale from my boiler. The engineer replied, yes, but (a
bunch of technobabble) The question was asked again and again and
again. Finally the engineer replied Do not use hydrocholic acid. It
will eat hell out of your pipes.
 My guess is vineger is slower, but just as destructive. Commercial
scale removing chemicals also are likely to cause leaks. Your best bet
may be some supplimental heating, and limp along as long as you can
with the partially clogged system. Scale is the reason few new
instalation use steam or hot water heating. Usual scale is calcium
carbonate, but it is possible your water has lots of calcium sulphate.
Calcium sulphate is slightly soluable in water, so using distilled or
deionized water in your heating system may remove part of the scale.
If you try to remove all the scale, the distlled water will corrode
your system. If you really want to try it; I suggest carbon dioxide
gas or baking soda = sodium bicarbonate as calcium bicarbonate is
slightly soluable in water, but you will need to flush the system
several times. Don't use any kind of acid or alkali.   Neil

You could try Calgon in the water. This is available nearly everywhere
to prevent scale build up in washing machines and dishwashers etc.
Alternatively you could try the disodium salt of EDTA (ethylene
diamine tetra acetic acid). This is a type of chemical known as a
chelate (claw) and acts by attracting but not chemically combining
with metal ions in solution. Simply put it draws them into a lobster
pot type molecule from which they find it difficult to escape. More
calcium will dissolve to maintain the solubility which will be mopped
up by the EDTA. This is not a dangerous chemical but is somewhat
specialised and will probably only be available from a chemical
supplier. If you notice an improvement in the temperature performance,
then flush the system to be on the safe side before leaks occur.

Hope this is helpful.

cf

Sounds like the valve is full of mineral deposits. Replace it. If the
entire radiator is clogged, hydrocloric acid (muratic acid) will
dissolve it but it will need to be immersed in a vat of acid solution
and dunked in and out, followed with a water bath, this is expensive
and dangerous. The fumes alone are dangerous.

You're better off replacing the radiator if it's clogged. If the pipes
are clogged you'll have to replace the entire system. If you do this
don't use tap water in the system or it will all happen again.

How about thinking like a heating tech. What did the gas co say was
wrong? You suspect your pipes are clogged? Has a professional
confirmed this? Is it a steam system ? Or hot water system? We know it
is not a furnace, they use forced air, not radiators. Has the system
been bled? Are the vents operational?
If it is steam, is the trap clear?

The only thing I can think of is spot heating.

This is an interesting solution, these are heaters in winter and air
conditioners in summer.
http://www.portableairconditioners.us

Don't know if this is really what you had in mind, but it beats freezing or boiling.