Older radiant slab heating systems

[cfabe]

I am house hunting and looked at a house recently that was a slab-on-grade with radiant heat in the slab. The house was built in 1947. The piping exits the slab as two (supply,return) approx 1.5" diameter pipes, that appeared to be copper, but I'm not 100% sure as they were painted. It appeared to be just one zone. There was an approx 20 gallon water tank hanging from the ceiling above the boiler, and the boiler itself was rather old, possibly original. What kind of concerns can there be with a system like this? Obviously I'm concerned about the condition of the piping in the slab, can this be pressure tested? I saw something online about helium testing too.

The upstairs in this home is unfinished but is clear-span and of suitable height to finish into a generous master bedroom suite, perhaps 400 sqft, which I intend to do if I purchase the home. How would one add heat to the upstairs on a system like this? I think I have seen plywood underlayment that had channels in it for PEX, would that be compatible with the system that's installed?

Am I correct in assuming that the slab is probably not insulated on a home this old? Will this be very inefficent? I believe the exterior walls of the house are also solid masonry (they were in the upstairs). There was insulation in the roof rafters, but I couldn't see down into the wall cavaties since there were floor boards. Is this 1100 sqft house going to cost me a fortune to heat?

Interestingly, on the deed the home is referred to as being in the "Radiant Homes Inc" subdivision. Thought that was interesting, I assume all of the houses were built with this new 'wave of the future' system.

Chris

[Larry Ashcraft]

Radiant heat got a bad rep early on as the concrete would settle and the pipes would crack.  It came back with a vengeance in the 90's with the advent of new technology (such as PEX).

We installed it in our 1933 Craftsman about five years ago, but due to lack of insulation in the walls we still have to supplement it with a catalytic wood stove and (recently) with a portable infrared heater.

If this house does not have any leaks in the system, it may be alright for a while.  However, I think you may have trouble down the line as copper pipe is usually given a service life of 50 years.  There are ways to install the heat upstairs, look up radiant heat on the internet.  Ours was from a company called Radiantec, located in Vermont.  They are a very good company to work with.

[Mabs2]

Mandatory answer:  Deal with the system for now, but save up for a geothermal heat pump.
Unfortunatly, I don't know enough about boiler systems to tell you anything more than that.

[280plus]

Copper had problems because the lime in the concrete attacked the copper. I'd be surprised if it didn't leak. You can use plain old air from a little air compressor to do leak checking. The plywood with channels is VERY expensive. Your best bet is to design the floor for extra weight  load and pour gypsum (gypcrete) over tubes stapled to the floor. You can also "staple up" tube underneath the floor. That's probably the cheapest way to go. I recommend radiant heat under tile floors only. Rugs are insulation and require higher water temps and hardwood can have splitting problems if the home is not kept at 50% humidity during the heating season.

Hope this helps. Ask more if you still have questions.

[K Frame]

The "water tank" above the boiler is the expansion tank. When it's operating correctly, it is partially full of water, and partially full of air.

As water heats, it expands. You either give it some place to go (the tank) or it will trip the pressure relief valve. When the system cools, it sucks in air, and you can get an air lock.

DEFINITELY have the system pressure tested. If it leaks, you've got a very good bargaining position. If it holds well, you have the single most comfortable method of heating available.

Levittowns used to be built with in-floor radiant heating. Unfortunately, over the years most systems have developed leaks and have been abandoned.

Repairing or retrofitting an old slab system can be frighteningly expensive if it does leak, and you lose headroom as you have to raise the floors by a minimum of 2". At that point I feel the best way to go isn't forced air heating that so many push, but baseboard hot water, the second most comfortable heat source there is.

If the slab isn't insulated, it will be FRIGHTFULLY inefficient. Given that there were none of the plastic type insulating materials in those days, it's doubtful that it's insulated.

As for adding additional heating capacity, you need to figure out if your current boiler can handle the extra heating load. I have a very funny feeling though, given the house's tenuous slab insulation, that it's going to be very much oversized to deal with the heat loss to the ground.

[280plus]

I've heard of so much heat being lost through an uninsulated slab that the houses have a snow free perimeter where flowers will grow in the middle of winter.

[cfabe]

Thanks for the input. If I decide to pursue that house I'll have to get copies of the utility bills to see how bad they are. The house had some other issues as well, may just pass on it. I do like the idea of radiant heat though. If I ever build I'd strongly consider it. In the house they had carpet and wood laminite on the floors.

[K Frame]

You are limited in your choices of carpet somewhat, but normally you can put W2W on radiant without too much loss in either heating ability or efficiency.