Starting my radiant research and seeking advice

baltik

I am located in SF bay area near the ocean so it never gets very cold here but it's consistently chilly. My town's average lows are 48 during the coldest months though things do drop into the 30s for a few days.

3100sq ft house is currently heated using a 5 ton heat pump but downstairs is significantly colder than upstairs (sun exposure plays a role here as well).

Separately we are going to be doing a 600ft addition downstairs and will likely use radiant for that.

What I would like to accomplish - use staple up radiant in existing downstairs area (600ft) to supplement the forced air. Use radiant in slab for the new addition as a second zone also 600ft.

Questions:
Is mixing and matching radiant floor types practical?

My current domestic boiler is a Navien npe-240a2, could that do double duty for radiant as well?

Gas and electric are extremely expensive in my area, but I do have excess solar electrical supply, is there a vetted heat pump option for my modest needs? Could i do a hybrid water heater like the Rheem Platinum?

hot_rod

yes, air to water heat pumps are an option. First a room by room heat load. Then a design using heat emitters requiring a SWT 120F or below.
properly designed and installed you should get heating, cooling, and DHW from a hp system

baltik

Thanks for the advice - are hybrid water heaters with built in heat pumps like rheem platinum an option for smaller systems? or is the recovery time just too slow?

EdTheHeaterMan

I did something very similar. Addition with slab on grade. I put tubing in the slab. Specified an additional 2" excavation to account for 2" foam insulation for the entire slab area( the masonry contractor wanted to do 2ft perimeter of slab. He had to come back with BobCat to excavate the entire slab to accommodate the insulation. (He just did not understand the concept).

The balance of the home was staple up. I used a simple piping design with a mod com boiler set at my desired desired water temperature. The ODR curve was set accordingly. The floor in the addition slab was quite comfortable and even temperature. The staple up with Hardwood floor was less effective, but only by 2° on average. During extreme cold (Below 20°F which you may not experience) I dod need to employ the existing furnace to maintain the desired temperature on the staple up sections. the Slab was always comfortable.

I hope this helps.

Mr.Ed


PS. If your existing boiler is currently heating higher temperature emitters that will still be in use, you will need to add some sort of mixing valve or other device to simultaneously provide 2 temperatures from the same boiler.

baltik

Got it - so on the boiler quesiton, I know i will have to do a heat loss analysis to be 100% sure but, theoretically could a hybrid heater be used for hydronic? they rheem's are only rated for 4,200 btu/h

Could a navien 240 (199,900 BTU/h) serve both domestic and radiant? presumably through some sort of heat exchanger

EdTheHeaterMan

baltik said:

Got it - so on the boiler quesiton, I know i will have to do a heat loss analysis to be 100% sure but, theoretically could a hybrid heater be used for hydronic? they rheem's are only rated for 4,200 btu/h

Could a navien 240 (199,900 BTU/h) serve both domestic and radiant? presumably through some sort of heat exchanger

I would stay away from using something designed to make Potable Hot Water or Domestic Hot Water (DHW) to do space heating of any kind. The control design and implementation will be problematic. With your last query, I assume you do not currently have a boiler for any type of space heating... correct?

Then I would recommend the NCB-H Combi or the NFC-H Combi from Navien for heat and hot water, or the NFB or NHB for heating only. I believe the 240 you refer to is the NPE 240. That is a DHW only appliance

hot_rod

The heat pump water heaters probably would not have the output that you need.

An A2WHP is a different device. Typically 3- 5 ton units that can heat or chill the system fluid, some provide DHW.
Here is some reading on how they work and are applied. They are becoming popular in a climate area like yours. An in areas where there is an electrification push.

https://www.caleffi.com/sites/default/files/file/idronics_27_na.pdf

Zman

baltik said:

Got it - so on the boiler quesiton, I know i will have to do a heat loss analysis to be 100% sure but, theoretically could a hybrid heater be used for hydronic? they rheem's are only rated for 4,200 btu/h

Could a navien 240 (199,900 BTU/h) serve both domestic and radiant? presumably through some sort of heat exchanger

Heat pump water heaters are more efficient than resistive electric when they are taking heat from the air around the heater and transferring it to the water inside. If the HPWH is located in the same space you are trying to heat, well, you can see the problem...

baltik

Zman said:

baltik said:

Got it - so on the boiler quesiton, I know i will have to do a heat loss analysis to be 100% sure but, theoretically could a hybrid heater be used for hydronic? they rheem's are only rated for 4,200 btu/h

Could a navien 240 (199,900 BTU/h) serve both domestic and radiant? presumably through some sort of heat exchanger

Heat pump water heaters are more efficient than resistive electric when they are taking heat from the air around the heater and transferring it to the water inside. If the HPWH is located in the same space you are trying to heat, well, you can see the problem...

Definitely thought of that - the HPHW would be in a separate area and vented outside. I was just curious if they are being used in a radiant application successfully

hot_rod

I played around with a HPWH in my shop, hoping to use it for radiant heat. It was inside the shop for the testing.
The compressors are tiny, about the size you see in drinking fountains I think 1/2 ton capacity. Pulling about 2A when running. It took 12 hours to raise the tank from about 50F to 120F.

Discharge air was about 48F. Fairly noisy also.

Venting it outside may not do much, and bringing in outside, cold air would drop the COP. They use the heat from the space for the exchange.

HPWH were described to me as "trickle chargers." Unless you kick in the resistance also, they are a very slow recovery.

Jamie Hall

Bottom line here, and nothing new. Water heaters -- heat pump, gas, oil, resistive electric, whatever -- and water heaters and designed and built to do that. They are not designed for, not intended to be used for, space heating. The only time they should even be considered is when their capacity is well within the anticipated load, and when the radiation -- whatever kind is contemplated -- will have a supply temperature of less than 140 -- and a return temperature preferably less than 60.

baltik

I still don't quite understand the advantage of having a Navien NCB or NFC for radiant & DHW vs just using my standard NPE 240 and a heat exchanger to separate the 2 sources of water. My existing navien has a similar BTU output and similar turndown ratio. so I am still puzzled by the differene

Alan (California Radiant) Forbes

Typically, on-demand water heaters used for hydronic heating are not happy because on-demand water heaters like a big difference between incoming water temperature and outgoing water temperature (ΔT). If there's not at least a 40°ΔT, they short cycle which shortens their life.

Alan (California Radiant) Forbes

Tempting to use your Navien to heat the radiant, but I would install a small boiler to heat the existing downstairs and the addition. The water temperatures for those two zones could be the same, but it will depend on the heat loss of the existing second floor and which staple-up product you use. I recommend Ultra-Fin. Heat loss calculations will be a must.

Lance

Is mixing and matching radiant floor types practical? Yes, I have three types of radiant, one which uses any water temp even 180F, one staple up and another surface floor under floor tile the last two use temperature controlled loops 110-120F. My barefoot wife is very happy.

My current domestic boiler is a Navien npe-240a2, could that do double duty for radiant as well?
Mfg should answer this, but almost anything with the correct controls can work.

Gas and electric are extremely expensive in my area, but I do have excess solar electrical supply, is there a vetted heat pump option for my modest needs? Could i do a hybrid water heater like the Rheem Platinum? with the latest heat pumps able to do more at lower temps many options are open, but you have no sub zero weather. Remember we live on the floor. Heat in the floor even in a cool room will make us feel comfortable. Just realize the ideal comfort zone is not just the temperature but the proper humidity which is best between 45-55%RH. Still too cold? I here jogging in place can be warming.

Geosman

Thanks for posting your question. First, the HE water heaters are not sufficient for use as radiant heat sources. Your Navien NPE with its internal hot water storage tank and controls for DHW recirculation, is set up to manage a hot water air coil and with the correct Navien controller it should be capable of managing radiant heat for both staple up and for radiant floor heat.
Combining a unit that produces domestic hot water with radiant floor heat has some hazards. Not only does it expose the floor tubing to the full pressure in the domestic system but in using it directly with domestic water shared between floors and fixtures will allow water stagnation in the floor tubing sections.
This can lead to the growth of bacteria during the off season. Of particular concern is the growth of Legionella which, if mixed with domestic water, particularly in a bath shower, could lead to chronic infection. For this reason, systems that combine domestic and radiant loads should be separated by a heat exchanger so that the domestic fluid used to transfer heat to the radiant side of the heat exchanger is minimized as would be the potential for bacterial growth during the off season.
I've made several such applications using a TACO X Block to separate domestic from the radiant side of a system with great success. https://www.supplyhouse.com/Taco-XPB-1-Taco-X-Pump-Block-1-25-HP
Unfortunately these are on back order from this source but when available they provide an excellent means to separate domestic and radiant circuits. The tech line at Navien should be able to provide advice on connecting them with your system and the Navien H2 air control (if needed), found on page 81 of your NPE installers manual.
As for using staple up tubing under hardwood floors....I see it as a wasteful exercise and of limited results. I prefer using aluminum reflector plates and have replaced many ill-advised staple up installations with aluminum plates with great success and to the delight of the owners who were sold on the lower first cost of doing staple up. As a bonus for using reflector plates the fluid temperatures used for reflector plates and radiant floors are similar so there will be no need to run temperatures to 180 for staple up and 110 for the floors as 110 should do very well for both in your area.

baltik

Super helpful, thank you. One more question about radiant as a whole vs forced air. One of my issues with my setup is that the forced air heat just rushes upstairs, does radiant help reduce that effect or would I have similar heat loss due to air rising?

Dave Carpentier

Heat always rises. The beauty of in-floor heat is that it starts low and drifts up, increasing our comfort. If you have high-mass (a slab), or a lower-steady flow in a staple up, then the comfort is fairly continuous. So, even though the heat is going to go "up" regardless, we get to spend more time in the happy zone.
We have in-slab on our main level, and forced air on the second level. The second level's floor gets some heat from the main level. The heat does migrate up thru the open stairwell , but I installed air returns in the main level rooms, and balanced things (restricted the upper floor returns) so that some of that upper-level heat does seem to flow back down (ie, the lower level is slightly depressurized compared to upper). As a bonus, having air returns in the lower rooms helps to circulate the air too (in-floor only can make for stagnant spaces, I think).

hot_rod

Heat travels to cold, in any direction. The greater the temperature difference, ∆T, the faster the energy travels between hot and cold.

Hot air rises, aka forced air heat A temperature check at the ceiling of a radiant floor heating system, compared to a forced air system, is an eye opener.

Dave Carpentier

hot_rod said:

Heat travels to cold, in any direction. The greater the temperature difference, ∆T, the faster the energy travels between hot and cold.

I've always thought of the heat from in-floor as rising, but didnt consider the direct effect of delta within each small cube of space within the room.
With forced air, it's a bag of hot thats usually shot upward from below windows. So the delta near that bag is high and its already heading upward.
With in-floor the heat starts across the entire room floor and , if btu in is near btu out for the room, the delta is very small in any cube.

When we built the place 20 years ago, I was just going to go oil forced air on both floors. My Scottish pipefitter buddy that was helping with construction kept twisting my arm towards in-floor at the very least on the slab (main floor and garage). Im glad I took his advice.
Over the years, I've tried to convince friends that were building to go hydronic but they typically say something like "oh, no.. im just going to put a simple furnace". Simple is good, of course, but man.. spread the pleasure of hydronic out over a 20-40 year span that you might be in the house..

hot_rod

Dave Carpentier said:

Heat travels to cold, in any direction. The greater the temperature difference, ∆T, the faster the energy travels between hot and cold.

I've always thought of the heat from in-floor as rising, but didnt consider the direct effect of delta within each small cube of space within the room. With forced air, it's a bag of hot thats usually shot upward from below windows. So the delta near that bag is high and its already heading upward. With in-floor the heat starts across the entire room floor and , if btu in is near btu out for the room, the delta is very small in any cube. When we built the place 20 years ago, I was just going to go oil forced air on both floors. My Scottish pipefitter buddy that was helping with construction kept twisting my arm towards in-floor at the very least on the slab (main floor and garage). Im glad I took his advice. Over the years, I've tried to convince friends that were building to go hydronic but they typically say something like "oh, no.. im just going to put a simple furnace". Simple is good, of course, but man.. spread the pleasure of hydronic out over a 20-40 year span that you might be in the house..

Dave Carpentier

Wow ! Thats wilder than I expected.
So not only is in-floor more efficient due to not requiring quite so much btu for our bodily comfort, it also keeps a lot less heat up on the ceiling (and top part of the exterior walls) where the higher delta can drive it thru and be wasted.

baltik

Geosman said:

I've made several such applications using a TACO X Block to separate domestic from the radiant side of a system with great success. https://www.supplyhouse.com/Taco-XPB-1-Taco-X-Pump-Block-1-25-HP
Unfortunately these are on back order from this source but when available they provide an excellent means to separate domestic and radiant circuits.

Thanks again for the helpful and practical advice, the installer I spoke with keeps pushing me for a full replacement of the navien, claiming that the external heat exchanger will make the system extremely inefficient. My counter is that the combi units already use internal heat exchangers so the right setup shouldn't make a big difference in efficiency. Given you have experience in this area, would love some real world feedback.

Another thought I had was the use of an indirect water tank (can be used either for DHW or radiant) is that a better alternative to a heat exchanger setup?)

hot_rod

properly sized and applied a plate HX can be very efficient. Close Approach sizing can get the B side temperature within a few degrees of the A side input, very little loss.

The answer lies within these pages, along with long hand math, to calculate performance.