Hi - I am no expert by any means, so I hope some do answer but I can share my experience with you. We are doing a gut renovation and had wanted to use hydronic radiant floor heat in the main living areas and to save some money, use either radiators or hydro-air in the rest of the house. (The air handlers and ductwork would be used for A/C, too.) We chose a Buderus high efficiency LP boiler and were told that we'd be defeating the efficiency of the system if we mixed radiators with radiant floors. This was the opinion of several people we asked. We went all-floor heat. I don't know if this helps but we were asking the same questions. Good luck.

Hi ellessebee,

Thanks for your feedback. That is a bit of a disappointment, especially since I was just talking to a rep from one of the top radiant flooring manufacturers who told me it wouldn't cut the efficiency at all. But of course he has a product to sell. I would bet you will be very happy with your choice to go all radiant, but unfortunately getting into the floors of the rest of our house isn't really an option for us.

Since I'm getting some conflicting info are there any others out there who can weigh in on the efficiency of a mixed system vs. one that is just radiators.

Thanks.

I have no experience with a mixed system, but I would think you are going to loose some efficiency. The way I look at it, if the boiler heats the water to 180 degrees, all the radiators can operate and radiate the heat. If you have a mixed system, the 180 degree water has to be cooled down for the radiant system. The cooling down represents a loss of energy and efficiency.

Talk to a heating contractor who has done mixed system. You want to be confident the system is done correctly.

Any reason why you need a 65 gallon hot water heater?

I would encourage you to keep all your old 1930âÂÂs cast iron rads and yes you can use your cast irons and have in-floor radiant with modern hydronics - while operating at reasonable efficiencies.

I would suggest finding an HVAC contractor that is both knowledgeable and passionate about modern hydronics.

SR

fsq4cw,

Thanks for the feedback. Can you give me some background on why you think we should keep the old cast iron rads? Are they more efficient or is it just that they are as good as the Runtals and we are wasting money replacing them? I certainly like the idea of saving money and putting it into the floor.

Thanks.

Hi Mike,

We currently have a 50 gallon traditional hot water heater and it works well, but runs out if someone takes an exceedingly long shower. Currently we also really only have one bathroom used for showers, but will have a new master bath so I would expect as with simultaneous showers going on we might need it. I'll check with our HVAC guy, but it is probably because of the added bathrooms that he was stepping up the size.

Does that seem too big? I guess if the boiler is sized for the hot water and not the possibly smaller need for heating that would reduce efficiency.

Your old radiators would be just as good if not better than a new runtal. The only reason to change them would be they are ugly or you want something that does not look like a radiator.

If you have a separate 50 gallon hot water heater, then I see no reason to change it. I am not an expert in this area, but I have always debated the pros and cons of having the hot water tank integrated with the boiler.

I have an 18 year old 40 gallon hot water heater and two showers. We never seem to run out of hot water, but then again we don't try to take two showers at the same time. Does the shower have a low water flow head? I think this makes a big difference for those who want to stand under the water for 20 minutes.

Regarding the aesthetics of keeping your old radiators, it is only my personal opinion that they should be kept, however, you must decide for yourself. Keeping the old rads preserves the look and feel of your heritage home. It may also preserve or perhaps even enhance the resale value of a heritage home. The reason for taking them out might be if youâÂÂre gutting the place and while it will look like a heritage home on the outside, it would be completely modern on the inside.

The technical reason to keep the old rads is that they are usually the large ornate heavy cast iron rads that require the lowest water temperatures of that genre and as such are the most efficient. Modern designs that will heat with even lower water temperatures are now also available. These designs are primarily but not exclusively for geothermal hydronic systems. The lower the required water temperature the less energy consumed. Mixing in-floor radiant and your old cast iron rads may be the best choice from energy efficiency, monetary and heritage preservation points of view.

Find the hydronic heating specialist that is on the cutting edge of modern hydronic design and installation techniques. This should include controls as well. Your system will not only be efficient, it will be a work of art - you wonâÂÂt be sorry!

IMO

SR

I am curious for an update in your decision! I've got a 1900 home we are gutting (but keeping floors) and I want to keep the rads. But architect and contractor want something different bc the rads take up so much space...

Who owns the house, the architect, the contractor - or you!

SR

:)

I think a home built in 1900 should have ornate moldings, high ceilings, and radiators. You can probably get smaller radiators and possibly recess then into a wall.

Thanks mike_home. Nothing ornate about our house and unfortunately no high ceilings but definitely big heavy cast iron radiators!

@mecoda, I'm a few hrs down the road in Roanoke. About to do a similar project on a 1920 Craftsman. For some reason some of the rads were taken out leaving some rooms with no heat. I found some smaller rads for $200 for 7 from another house being switched over to forced air so I resized, cleaned, painted, pressure tested & put in place. I plan to connect 4 of the rads & run radiant floor heat in a bathroom expansion & a new master closet/laundry addition. I bought a 6 line stainless manifold on eBay for about around $150 I think. For the rads I'm gonna use a combination of oxygen barrier pex behind the walls & old iron pipe for anything exposed. Instead of a mixing valve, I'm considering (you might also) either connecting the radiant floor heat to the return side of a nearby rad since it would be cooler, but then again, I'd be able to adjust the heat on the manifold by slowing the flow rate. I'm doing it all myself so t's definitely a learning as you go process.

My rough calculations show it is not horribly expensive simply to add a second boiler for the radiators, especially since in our case the radiator rooms are guest bedrooms and temperature can be set quite low when guests are not present. We have a boiler room with enough space for a small boiler with hotter water and its own manifold seems a lot simpler than mixers and wasted energy. The other option would be a separate system to "bump" the water temperature from the radiant boiler from 120 to 140 for the radiators, but I cannot find any products that do this. Any opinions and/or information?

It would have been best to start a new thread, this one’s over 9-yrs old!

All you would really have to do would be to add another radiator to the rooms in question that would make up for the Btu required due to lower water temperature.

IMPO

SR