Radiant AND Radiator Water Temps

Mark M

I've heard only a little about this concept and I understand that it anticipates the changes in temperature inside by monitoring the outside, but I don't quite get how it saves on fuel bills. I'm assuming that it gradually raises the inside temperature (when it's getting colder outside) as opposed to reacting to the dip in inside temperature. Does this really save that much? (thanks, and sorry for the late reply)

Mark M

Radiant AND Radiator Water Temps

I have a 100 year-old house in Wisconsin, fairly well insulated and will soon need a boiler replacement. I want one source for domestic hot water, radiant floor heat on 1st floor but keep my radiators on the 2nd so I don't have to rip out a floor or ceiling. What's the best way to satisfy the two water temperature needs? I know about mixing but wondered about any other ways, including two tankless heaters running at different temps. Thanks!

Brad White_120

Mark, you could

go the route of two heaters (tankless? Do you mean indirects which are tanks?).

If such is the case, that is a lot of water to maintain at temperature which not only costs energy but delays response time.

Depending on your floor radiant (thin-slab, staple-up, gypcrete) and the associated water temperature versus what the radiators might need, I would let that comparison dictate your water temperature.

In other words, if the radiant floor is under-floor/staple up or thermo-fin rather than in-slab or above the joists, that might require a warmer temperature than the radiators.

This is especially true if your radiators are oversized (presumed cast iron). Thus you would run your warmer water for the sake of the floors and use a mixing valve/manifold setup to serve the radiators with outdoor reset. May be one of those times when floor heat takes hotter water than radiators.

Technically, each might benefit from a manifold setup for ease of installation if nothing else.

That is what I would do; two temperatures via manifolds.

My $0.02

Brad

Mark M

Thanks Brad. To clarify, I do have old oversized cast iron radiators, was going to staple up PEX under the floor, and was referring to tankless heaters (only as one option) where I think a small reservoir tank is recommended for radiant side of the heating system. So, I hope I'm not having to maintain too much standby water. But, I'll consider a boiler or dual-duty HW heater, too.

I assumed the temp. difference to be 120F (radiant) vs. 180F for radiators, so I was surprised to hear you say that the floors might actually need the warmer water (but perhaps not 180). Sounds like you think the floor should be warmer than 120(?)--especially since it's a retro installation. Is it possible that both systems might be happy with a single temp. (with one heat source) and allow each of the 2 systems to run its respective pump as long as necessary to satisfy its thermostat? Then I can simply mix it down for domestic hot water.

Brad White_9

Warmer water to the floors

I agree, Mark, that at first the concept of using warmer water for floors versus radiators was counter-intuitive. The concept was brought to me by fellow Wallie Paul Lessard. I had to think about it too but this is why:

The radiators in my case are 60 to 70 percent over-sized, 100 percent in some cases. Thus, I can use 130 degree supply water if I want, on a design day and with TRV's on the radiators.

The floors in question have two layers of softwood (pine and yellow pine) plus rosin paper, carpet and pad. OK, the carpet goes eventually, so let's discount that.

According to my Rad Pad, the basic R value for staple up with plates at 6 inch spacing is 2.0, plus the wood layers at another 1.6 R value. Total R value is 3.6. My floor heating load is 20 BTU's per SF for the area in question and this requires a floor temperature of 81 degrees F. To achieve this with the tube spacing stated, I need 145 degree water to achieve this output. To get that full 15 degree premium, I have to fire the boiler to that point and mix-down for my radiators.

Again, it all depends on your "radiation to heat loss ratio" but it was amply demonstrated to be entirely possible to have that situation. As you said, you may find you can get by with "one flavor" (temperature) and do perfectly well. But first, you have to know...

Oh- if using a combination DHWH for domestic and heating, use a brazed plate exchanger. DO NOT intermingle domestic water into the heating system.

Mike T., Swampeast MO

Nice heavy extruded aluminum plates (like Thermofin) can certainly keep supply temp requirement down compared to bare tube staple-up. In my house I had to use copper in the Thermofin for the radiant floors to work at the same temperature as the iron rads.

Fortunately, ground floor heat loss is generally lower as there is no ceiling loss. Unfortunately, the dead men knew this and your upstairs rads were likely sized for operation without any insulation--thus they become even more grossly oversized with an even lower temperature requirement.

You're likely to need a two-temperature system in any regard but I would try to engineer the radiant to work at temps as close as possible to the radiators. Thhis especially true if you ever plan to use a high-efficiency condensing/modulating boiler.

Mark M

Thaks Mike (and Gary),
Mike (or anyone), the aluminum plates make sense to me. Many companies and people are pushing them, but one seemingly very experienced installer (http://www.radiantdesigninstitute.com/) says hogwash to these plates. He says they are unnecessary, make noise, and that you only need to staple a full loop (two parrallel 1/2" PEX tubes) between every two joists. Any thoughts to that thinking?

Thanks in advance.

hr

Did that company come by

and do a room by room heat load for you, and discuss options? If not they are just guessing as to what you home really needs

I also believe the extra cost of extruded transfer plates is well worth the money spent for most applications.

Virtually every radiant tube manufacture offers extruded plates, and most have phased out the thin noise maker flashing gauge plates.

Oddly I recently looked at a job suppled by the company you mentioned and it was supplied with thin "aluminum transfer tissues"???

hot rod



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

ALH_4

Well

After reading a few pages on that site, I would recommend not visiting it anymore. One reason given for not installing low temp radiant above floor in gypsum is that it "Requires expensive and confusing mixing valves and controls on boiler". If these are confusing, this person has no business in the heating business. Also this person has had failure problems with gypsum? Something must have been wrong. It looks as if he is a proponent of suspended tube radiant. Yes it is easier to install. No it will not perform anywhere near any system that provides direct contact between the tube and the floor.

Hot Rod's thermal images completely refute this site's assertions about plates. And on the same page as he says that plates have no benefit he shows some sort of plate in his "staple-up" diagrams.

-Andrew

Ron Schroeder

Mark here is a good read

http://www.heatinghelp.com/pdfs/247.pdf#search="radiant floor heat staple up vs plates"

Mike T., Swampeast MO

Do you currently have radiators on the ground floor? If so, why are you removing them?

What is the construction of the actual ground floor floor? 100 year-old homes frequently have floors so thick that even heavy extruded plates will need MUCH higher temperatures than your upstairs radiators.

Mark M

hot rod,
No assessment has been done by this or any contractor yet. I'm glad to hear that there is strong opinion for it.

Mark M

Bruce, excellent read indeed. Thanks. (interesting to see that people are quite split on the issue)

Mark M

Mike, I do have radiators on the 1st floor and I have a 3/4" subfloor with 3/4" Maple on top, no carpet. Why am I removing them? My bottom line is efficiency. I have to replace my boiler soon anyway and after a $520 gas bill (peak) last Winter, I'm looking at all options. And that was keeping the thermostat at 65F. Incidentally, I wrapped my basement-exposed radiator feed and return pipes before last Winter and I think my house was actually colder. I'm wondering if that backfired. Anyway, the potential difference between water temps is what brought me to The Wall to begin with. Given all other factors the same, do you think that radiant heat is more efficient that the traditional boiler & radiators in an older house? BTW, I also like the idea of combining all water heating into one unit.

Mark M

Thanks, Andrew. Well, I missed the part about suspended tube radiant. I saw his stapled-up photos and my impression was that he suggests going with two PEX passes between every two joists instead of one pass with plates.

Mark M

Brad, thanks for the insight. That helps a lot. And I was assuming that I would have to use heat transfer. I know some push the "open" system but the humidity (no A/C) in summer would ruin my floors with all that cold water sweating going on!

Mike T., Swampeast MO

With that floor construction I sincerely believe that your radiators will prove significantly more efficient as they'll almost certainly need lower supply temps--even if you use copper tube in heavy extruded plates.

Install TRVs (thermostatic radiator valves) on ALL radiators. Use a Viessmann Vitodens (presuming gas is your fuel). MAINTAIN 65F or so via the TRVs and enjoy WONDERFUL comfort and AMAZING efficiency.

Such will not be inexpensive--but it should be VERY comparable to what you are considering and I can nearly guarantee that the option I suggest will be more fuel efficient and nearly as comfortable as the best radiant floors.

ALH_4

v=ir

Re-reading my post, it was prety negative.

When comparing plates to staple-up, think of heat like electric current. Air is an insulator. The heat is trying to get from the fluid inside the tube to the floor surface as efficiently as possible. The temperature difference between the fluid and the floor surface is analogous to the voltage. Your heat load determines what current you need between the fluid in the tube and the floor surface.

What do you do to maximize current-carrying capacity?

1) Increase the voltage, ie. increase the temperature differential. This means either making the room colder or making the fluid hotter. Making the fluid hotter reduces the efficiency of your boiler. Making the room cooler reduces your comfort.

2) To increase the current carrying capacity you can also reduce the resistance. Plates or concrete pours are fat wire.

For maximum performance you want to carry the greatest current with the lowest voltage.

Running two loops of Onix per joist bay will likely cost more than plates.

-Andrew

Mark M

Thanks for that advice. I've been looking at heat sources but hadn't run across that one yet. Sure would be easier to simply replace the source. As for TRVs, are they worth the expense and hassle? I wonder if they can even be installed with my old pipes (will this old stuff unscrew?) I have old manual valves on them today.

Brad White_125

The Value of TRV's

Expense and Hassle... How does one quantify that? Personally I find it all within my budget and skills.

I am installing nine TRV's right now. I got six done last weekend and will do the others next weekend. I budget roughly an hour and a half for each, some take more, some take less depending on how constrained they are. Moving the furniture sometimes takes as much time as disconnecting the radiator...

(The system is all drained and dry by the way....great place to start rather than one at a time....)

Break the old radiator valve unions, move the radiator out, spud wrench and an old wrench with a helper (five feet of 1" pipe for extra leverage) and I am good to go.

I am using Macon valves which use an Allen-wrench style Metric hex wrench tool for nice, positive spud insertion.

Expense varies, bodies run in the $75 to $100 range retail (wide range yours may vary) and the thermostatic heads vary as well, the remote sensing and adjustment types costing more. The standard heads (setpoint and adjust in one) are the least expensive and work when the valves are "horizontal angle" types, not the vertical types which give false readings. For a complete valve and head assembly, I would budget $100 to $150 per radiator.

The radiators I am working on have not been worked on since they were first installed in 1922. The valves go in with the same C-C dimensions as the original Capitol valves and the NPT pipe standard is the same... they so far have gone in very well. Just as Mike T. said, use a backing wrench so you do not loosen up unintended joints....

Worth it? I think so... Every room gets it's flow. They can level discrepancies between sizing/output and heat loss especially with constant circulation.

The system I am installing is a loop system so water not being used on one side or radiator will be available to the others instantly. I expect very even pressures, hence flow potential, all the way around the house. I will let you know when done in this case, but have them on my own house and have for years. Every room a zone essentially, albeit high limit in control. Best thing going just the same.

My $0.02

Brad

Mike T., Swampeast MO

I've yet to find an old hand valve that cannot be removed with reasonable ease. Do though ALWAYS use two wrenches in opposition to one another--one wrench on the valve the other on the pipe. The tailpieces are another thing... I just remove them along with the old tapping bushing and install a new bushing, but others say they don't have too much trouble getting the tailpieces out.

The advantages of TRVs are legion:

1) They're VERY tested technology, long-lasting, accurate and reliable. With some the "packing gland" can even be replaced without draining the system.

2) They allow room-by-room "zoning". Each room can be maintained at whatever temperature you desire. Yet, while each room is effectively "zoned", the boiler only sees the system as a whole--not a bunch of different zones. Considering the cost of zoning by other methods, the price is an utter bargain.

3) TRVs and pneumatics are the only control system I'm aware of that offer proportional flow control as inherent to their operation. TRVs are MUCH less expensive than pneumatic systems. Proportional control is the only practical way to restore flow in old converted gravity systems similar to the original design but with ever-improved balance. Given the age of your house, yours was likely a gravity system originally.

4) TRVs self-adjust for "unusual" losses and gains on a room-by-room basis. Within reason, rooms receiving high solar gain will not overheat; nor will rooms experiencing high loss (say due to heavy wind) underheat. Such a high degree of compensation is difficult with any other non-proportional control system.

Iron radiators with TRVs are ideally suited for condensing/modulating boilers. This is especially true with old gravity systems when the shell has undergone significant thermal improvement. Not only will the TRVs compensate for imbalances (be they original or "created" by the thermal improvements), but they will, with proper boiler adjustment, keep flow rates low and delta-t high while maintaining the bare minimum radiator temperatures required. Taken together, this allows a condensing/modulating boiler to truly thrive and deliver exceptional efficiency.

There are many condensing/modulating boilers. I recommended the Vitodens by Viessmann as there's good chance it can be directly attached to your system (provided you use TRVs on ALL radiators) using only the single built-in circulator. Not only does this reduce cost in materials, but it reduces the time required to install the system. It is an expensive boiler--probably the most expensive residential boiler--but its quality is superb and the radiant burner, heat exchanger and variable-speed circulator are all unique in the industry.

While TRV installation can definitely be considered a DIY project, boiler installation is not. If you choose to use a condensing/modulating boiler do your utmost to find a heating contractor who is already familiar with their use. Barring that, find one who is at least willing to do some study and learn something new.

Unknown

That website is very out of date. The old lightweight plates, Maybe you could make some claims like that. the transfer was better, but not hugely better with those things, and if you didn't do good design and installation, you could get noise problems.

The newer extruded plates out there don't make noise and can really, really drop those water temps as well as ensure output. Staple up tubing is quite obsolete in MOST (not all) cases, IMHO.

That said, it sounds like in your case you need to find out what temperature you can run those radiators at, then try to match it with the radiant. If that's not feasible, a two temp system may be in order.

Mark M

Excellent overview and advice Mike. I'm very heavily leaning towards simply keeping the radiators with TRVs and sinking the money into a top notch boiler. I was looking forward to the heat under my feet, but ....

Last thing, if the meter's still not running ;-), I would like to use the boiler for a dual system. Would you simply T off the boiler output with one side going to the faucets and one to a heat exchanger? I've convinced myself that it would be more efficient to consolidate. Is this only conventional wisdom?

Mike T., Swampeast MO

leaning towards simply keeping the radiators with TRVs and sinking the money into a top notch boiler

If my personal experience is any reasonable measure, such will provide a great balance between comfort and versatility while allowing nearly the highest possible efficiency.

I'll never downplay the comfort of large radiant panels (be they floors, walls or ceilings), but you can sincerely get VERY close to their comfort with your iron rads, TRVs, and the TRUE constant circulation of water AND heat. Certainly possible to add radiant floors in areas, but my most sincere recommendation (for efficiency) is that such floors MUST be able to work at or below the temperature required by the radiators. This can EASILY require complete re-engineering of the ENTIRE FLOOR SYSTEM in older homes (e.g. strip down to the floor joists).

I believe the "dual system" you're referring to is call "indirect domestic hot water". Certainly efficient and generally MUCH longer lived than "hot water heaters".

Considering your original post--and presuming you didn't expect this to be a complete DIY via "web radiant"--if you use TRVs, a top-notch condensing/modulating boiler and finest indirect domestic hot water tank, the final cost shouldn't be much different.

Steve L.

If you keep your cast iron radiators and set up your system with a control to adjust the water temp based on outdoor temp you should see lower fuel bills.

Mike T., Swampeast MO

Yes, you correctly understand the concept--as the weather gets colder, the supply temperature gets hotter.

"How" and "how much" fuel savings depend on the boiler, the system and how it's operated--there is however nearly universal agreement that it does save some fuel in nearly all applications.

If your system is a gravity conversion (as I suspect), it likely already operates with a sort of reset. This because the thermostat(s) are likely satisfied WAY before the boiler ever reaches the temperature set on the aquastat.

If your thermostat(s) turn on both the boiler's burner and the circulator(s), and there is no bypass line around the boiler, this is almost certainly the case. As is, there would be little to benefit from outdoor reset.

If however there IS a bypass line around the boiler or if the boiler is configured to heat to the aquastat setting regardless of a call from the thermostat, there are potential savings.

When reset really shines however is when it's teamed with a condensing/modulating boiler. Some form of reset is almost universal to such boilers. It's built in to most, an option on a few. The reason it REALLY saves in this instance as it allows the boiler to operate at MUCH lower temperatures. With condensing/modulating boilers, the lower the temperatures, the greater the efficiency. With typical sizing of old iron radiators (and hopefully added insulation and improved weatherization), the temps involved can be extremely low--lower in fact than most anything save radiant floors using tube in concrete slabs.