Cast Iron Radiators and Radiant Floor Configuration

FFJASON1

Greetings. I am working on a new install of PEX radiant floor heat in my 1940's colonial. After doing my heat loss calculations the radiant floor heat was going to be a little short to meet the loss (brick, block, and plaster exterior walls). So I was planning to convert my existing Burnham slenderized cast iron radiators from one-pipe steam to hot water. I am using 1/2" O2 barrier PEX with a separate manifold on the first and second floors. The manifolds would be supplied by 3/4" PEX. There are four PEX circuits on each manifold that are all about 260' each. Based on feedback from this discussion board, I am using heat transfer plates under the hardwood floors. The system will be supplied by a Burnham K2 120btu ModCon with a 35 gallon IWH.

The plan is to connect the radiators by 3/4" PEX loop with each floor on a separate zone. I intended to run the radiators a little cooler since they would be supplementing the radiant floor. I am hoping to run them in the 140 degree neighborhood with an assumed loss of 20 degrees. I would then like to use the return water of the radiators to supply the radiant floor at about 120 degrees which should eliminate the need for a mixing valve. This should also return water to the boiler at near 100 degrees.

Is this idea possible? I intended to arrange the valving to allow either the radiant floor or radiators to be shut off independently of each other. What is the preferred way of configuring the supplies and returns between the supplies and returns of both systems on both floors?

Thanks in advance,

Jason

hot_rod

Sure it would give you some additional heat. Ideally you want a radiator with top and bottom connections or one of the conversion valves. I have done a few with bottom only connections with an air vent drilled up top, eventually then whole mass of iron warms even without flow across bottom to top.

I run a cast iron pantry radiator in my bedroom with 120F supply and it warms nicely.

A home run system with TRVs is another option, possibly 1/2 pex runs to each rad. This assures they all get the same temperature. If you series pipe them you will run out of fizz before the end radiator gets supplied.

I believe Oventrop has a similar valve available stateside.

FFJASON1

Rod,

Thanks for the information. I will give that valve some more research. I did also think of a home run system for each radiator. Getting the the first floor ones is easy, the second floor might be a little more tricky.

What are your thoughts on how to supply the radiant floor manifolds off of the radiator return or do they need to be supplied separately with a mixing valve?

Regards,

Jason

hot_rod

To optimize the mod con you want to design around low temperature operation. I'd design both the radiant and radiators to run as independent systems. Are you considering outdoor reset?

Possibly a manifold upstairs and one down where everything is adjustable and able to be balanced.

FFJASON1

Rod,

I hadn't thought of a radiator manifold for the second floor. That would cut down on fishing all that PEX through the first floor walls. Thanks for the tip.

Yes, I intended to use an outdoor reset on the K2. From what I read they are really important to maximize the boiler efficiency.

What are your thoughts on thermostatic control of the floor heat and the radiators? Should they be tied into the same zone valves (one for the first floor and one for the second). Or keep both floors of floor heat on one zone and the rads on two separate.

Regards,

Jason

hot_rod

For ultimate comfort and control I would have an upper and lower zone. If you use a nice radiant manifold you could adjust and balance every loop. I'm not a fan of micro zones where every room would have a t-stat for the radiant.

The radiators would like to have a TRV on each, so no need for an actuator on the manifold for those loops. A TRV is a simple, non-electric, proportional zoning device, use them when you can.

This issue of Idronics has some good zoning ideas as well as a discussion on pressure regulated delta P circulators for zoning.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_5_0.pdf

vaporvac

Have you considered keeping the steam for the rads and add a Hot Water loop for the radaint flooring? What is currently wrong with your steam system?

FFJASON1

We did consider keeping the one-pipe steam originally but the boiler is shot and needs replaced. It cracked about 2/3's the way through last winter. Another consideration was that the current water heater is twenty years old and past its dependable service life. With the steam we always have trouble with a warm first floor and cold second floor as well.

So as part of a bigger (maybe to ambitious) that includes adding central A/C (SpacePak), some electrical upgrades for outlets and lights, we decided to change over the heat while we had full access. We are also taking the opportunity to add some insulation in the joist space ends too.