Steam Boiler + Solar Collector + ? = Radiant Floor System

Murray Gates

I have a 4 year old Weil-McClain steam boiler with seperate Weil-McClain Pro 40 water heater servicing a 3 story home and am looking to add radiant floor heating system during a kitchen remodeling project.
I've been told by contractors and plumbers that there a couple of options: 1) utilize cooler water from the existing steam boiler to feed the radiant heating tubes by way of a mixer to further cool the water or 2) install a seperate water heater.
I would like to investigate a third option but am having trouble finding the right mix of knowledgeable professionals to guide me...to install solar panels to heat water for the radiant floor heating.
Questions that come to mind are:
1) Size & Number of Solar panels required;
2) What would be the primary receptacle for the water heated by the solar panels and would this receptacle have to have a secondary heating mechanism such as gas when the demand is high but solar capacity is low i.e. cold cloudy days. If a secondary heating mechanism is required, could the existing Weil-McClain Pro 40 efficiently serve this purpose.

Steamhead (in transit)

Before you do anything

do a heat-loss calculation on the room in question. Everything else depends on how much heat is needed.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Constantin

Hmm

Like you, I am but homeowner. However, I would dissuade you from trying to heat your home with solar panels unless you live in the right area. Even then, solar panels usually pencil out to be more cost effective for year-round domestic hot water heating than space heat.

Like Frank, I would counsel you to figure out what the heat load is for the space. Next, I would determine what water temperatures you'd have to be running to fulfill that need (it depends on the floor emitter type, the heat loss, etc.). Once you know the temperatures required, you can go about determining which heating strategy makes the most sense.

For example, solar hot water heaters will not function during the night - you'd need a storage tank to act as a thermal battery for that purpose. Solar water heaters are also more effective at lower water temperatures, not the best scenario for most RFH retrofits. But, if your house is very well insulated, it could work.

So, my gut instinct steers you towards using the steam boiler as a heat source, provided that the RFH system will not overwhelm the ability of the boiler to still make steam. I'd reserve the solar portion for the DHW, i.e. have a look over at Butler Solar solutions for an innovative way to retrofit solar into extant water heaters.

hr

Stick with SDHW

solar domestic hot water. If the square footage of the radiant is 500 or less consider an electric product. Sounds like it would be a supplement to the steam anyways.

Sure you could mix steam, low temperature radiant and solar. It could be a complicated expensive project.

Solar storage becomes the issue as you need to store enough to get through the night at least. Possibly days or a week without sun.

SDHW is pretty much a 24/7, 365 use. Get a panel or two, an indirect tank as a preheat to your current water heater. Perhaps a 30% tax credit if you work it right

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Christian Egli_2

Keeping things charmingly simple

Here is for breaking down the problem into small manageable chunks.

It seems you already have everything you need. Your domestic hot water comes out of the Weil-McLain 40 tank, I am assuming you have a separate Weil-McLain heater, like 50, 70, or 90 000 Btu/h (and not bleeding steam boiler water to heat the domestic water tank)

With that in mind, it seems very likely that the kitchen floor can be heated off of the Weil-McLain heater, leaving the steam alone. Even 50 000 Btu/h should be lots to heat a residential kitchen, but I haven't seen your home and you should check your numbers. It is always good to listen to Steamhead. Also check your steam heat numbers with the proposed remaining radiation.

That will take care of the kitchen floor

Now you can treat the solar feature independently, like HR and Constantin suggest, by adding a solar pre heating tank on your domestic system. This, you can do with or without the kitchen project.

That will take care of the sun

All this, I think, you suggested yourself in your last point. Here is one more last item I would like to bring up. I understand you are redoing your kitchen and it currently has a beautiful steam radiator.

Why not maintain the radiator even with the addition of floor heat?

You can easily move, remove, reinstall a steam radiator whenever needed and following your any whims, providing the pipes are there... They are already there, why not keep them. I like redundancy and having radiant floor and a radiator combine to make for tailored heat. Now you can get away with even an under heated floor heat system (since that was your fear about solar), the glowing warmth of the steam will always be there for you. Thermostatic valves make all this foolproof.

What if removing your trusted radiator leaves you with no place anymore to dry your kitchen towels? You could even replace the cast iron stud with a more sober radiant panel or perhaps even a dainty artistic rendition of a towel warmer.

I really like your current setup, with stand alone steam and an indirect hot water tank fed with a separate heater. Good luck.

Mike T., Swampeast MO

I'll second the idea of keeping any existing radiator! They can be a bit difficult to work into a kitchen renovation, but the room seems generous in size so surely it can fit in somewhere (easiest if doesn't have to move though).

As Hot Rod mentioned, don't forget the possibility of electric radiant for floors. Unless your electric is utterly ridiculous in price, you'll get warm floors anytime you want without the steam system having to be on and you'll likely find it very cost-effective. Plus you'll hopefully still have your radiator to give the major portion of the heat.