Radiant Floor System - New Construction

[Lucas]

I'm getting ready to build a new house in the spring. I hope to have a Varmebaronen Vedolux 650 boiler with radiant floor heat. How should I install the radiant floor? Is there a difference in efficiency or cost between laying it in gypcrete, in a wood track system, or under the sub-floor between the joists? Is there any value to putting it between the joists so you can access the piping in the future?

 

[Nofossil]

I don't have any sense about relative cost, effort, or performance of the options you list so I'm waiting to see the responses on this one as well. I know that under-floor installs can be noisy if you're not careful because pex expands a lot as it warms up.

 

[Bad LP]

Mine was designed 10 years ago and is in gypcrete throughout the first floor (2 zones) and only in the two bathrooms second floor.(1 zone) We are also heating the large master shower floor. First floor is half tile, half mahogany. The bathrooms are all tile. The PEX is on 12" centers. The heat is very evenly displaced in the floor. In fact the only way to tell where the PEX is located is by using an IR thermometer or place your feet close to the outside wall edges. I am using air temp for the t'stats. We love it and so did the dog when he was alive. House is 10 yo. I was told to make sure to keep the tubing away from the water closets because of the wax ring.

The down side is this home is used on weekends year round so in the heating season I must bring the house up online and adjust the heat from 55 to 70 degrees 24 hours in advance however I can turn it back down hours before we leave and not know it. In the shoulder seasons the RFH is mostly useless. The LR wood stove helps with that and I'm seriously thinking of a HW coil being installed into the central AC air handler or I may change out the AC and install a heat pump for these seasons.

Lastly I had to insulate the underside of the 1st floor after the fact because so much heat was being transferred down into the basement below. I have zero noise in my floors but will tell you the PEX in the walls running up to the baseboard heat in the bedrooms and office is noisy.

A very good friend just finished a major entry, washer/dryer/laundry sink area, half bath, kitchen and family room renovation. They used a track/xfer plate system on top of the subfloor. Floor is tile in thinset. They were here this past Friday night for dinner and the topic came up. They mentioned that they can feel with their feet at every single PEX run throughout the space. I found this to be odd but haven't been there yet to confirm. They also love to run the wood stove in the family room. The RFH replaced FHWBB.

I do not know what water loop temp he is running and they just turned the system on so I don't know about noise. The company that did the install is very well known in the area and knowledgeable. He is also using a floor temp sensor.

 

[BHetrick10]

I have no experience with pour overs. Everything I have installed was under the subfloor. The cheaper "U" shaped transfer plates can be noisy. More plates, lower water temps are key. Extruded plates hold the pipe tight. They will not make noise, they do cost more though. Extruded plates still should be a lot less expensive than any pour over or warm board and similar products. I dont not like to run hotter than 115 or so through the floor if so you will feel where the tubing is. 80-90 is my preference if the home is insulated well enough to accomplish that.

 

[leaddog]

I tore down my tri-level 3 years ago and went single story open design. On all the new construction I went with in floor. I had a lot of 1/2 plywood so I ripped it into 8in strips and placed it over the sub floor with a 1/2 space for 3/8 pex. I bought 2 very large rolls of aluminum foil on ebay for $10 each and put that on top and when I installed the pex it pressed into the groove and then I placed a strip on top. I then placed laminate floor on that . I run 120* water or less and I can keep the house at 70* and be very comfortable as the floors are very even and warm. By turning up the heat it will raise the temp very quickly also. I also have a pellet stove I use for fire appeal and if I have that on I need to set the temp at 75* for the same comfort level because of the moving air.
Under the old part and the kitchen I have tile so I have staple up under the floor with homemade aluminum plates. I notice very little noise but keep the water temp under 120* but the recovery is slower. I'm using 1/2in for the staple up. I highly recommend doing infloor like I did. The only problem is if you have to cut into or screw any thing in the floor you must be very careful as it is harder to modify. The 3/8 is cheaper but you may have to run more loops. I don't remember the max but think it is 250ft.
It is the best and most comfortable heat I've found.
leadog

 

[Kelster]

Hey Lucas,
That's a classy looking boiler but jeepers - 2" wood only?

I install heating systems and there's a few rules of thumb that I adhere to and maybe they will help you in your decision making process. If cost is not object then go for the more mass in your floors. Concrete will obviously out-mass wood.

1) Budget 1' of tubing per square foot of floor to be heated and add 10% for mucking around at the manifolds, extra in front of the windows & doors, etc.

2) If you think you're going to need about 45 btu/sq.ft for a conventional forced-air system, you can get by with 25 btu/sq.ft for a radiant system.

3) if you're installing in concrete, gypcrete or w.h.y. you can get by with lower cost Oxy Barrier PEX tubing.

4) If you are installing on wood (with or without aluminum plates), then spend the extra $$ and go for the PEX-Aluminum-PEX tubing with 'no memory' you'll thank me when there's no creaking or ticking sound as the tubing heats-up.

5) If you have some big individual loads, like a Greenhouse, Pool or Spa then allow for some thermal storage - you can't go too big here. Think of it as a thermal battery for your heating system. Once it's charged, the battery takes over and you can coast, sometimes for a day or two without reloading the wood boiler

If your budget is tight, can't afford concrete floors, you can get by without the aluminum plates stapled to the underside of the wood floors. What's really effective is to staple Reflectix bubble/foil in the joist space an inch or so below the radiant tubing. Works amazingly well.

My 2bits.

 

[Woodfarmer1]

Kelster, what is your opinion on using a basement slab to act as heat storage?

If my slab is heated with say 120* water should I then turn off my circ pump and wait until I have used the heat from my boiler for the main floor before turning the slab pump back on again to circulate that water through my system?

Or what is the best way to use a slab for storage?

 

[Mike Fromme]

I'll be the devils advocate... Skip the wood boiler and storage. Take that money and whatever you planned for a backup system and go with a air to water heat pump and solar panels to offset its energy use.

Might be a little more money up front. But no fuel costs.

If you have free wood to cut, go for it. And then sell the wood to buy more solar panels.

 

[peakbagger]

I took a heating course last year on line taught by John Siegenthaler the generally acknowledged expert on residential and small commercial heating. He covered floor based radiant systems along with many other methods and uses it in selected places in his designs but he was actually a lot more of a advocate for other methods like radiant wall panel heaters located along the exterior walls and embedded wall and ceiling radiant systems. This is probably heresy to radiant floor owners who were brought up on steady diet of This Old House reruns but John had some very good reasons for this. Realistically I am not going to condense a 3 month course in an internet post but be aware that radiant floor is an important tool in a quiver of many approaches and it may not be the best fit if you want the best efficiency. Sure consider it in bathroom and an entryway but in others areas it is an expensive way to go and inherently is not the most energy efficient.

The primary issue is thermal mass and the slow response of radiant floors. The poured in systems have lot of mass and they end up being set and forget. Adjusting the output for daily usage just doesn't work very well as they take a long time to respond to a request for temperature change. This means the room is left at the highest temp required at one point in the day 24/7 whether occupied or not. This may be a good tradeoff for a small bathroom where the warm floor for 5 to 15 minutes a day is worth it to the owner, but that is a comfort decision version versus energy efficiency. The staple up tubing systems also have an issue that unless the floor coverings are optimized, the heat has a tough time getting to where its needed. This design also has a slow response time and the supply temps end up having to be higher than in other options. Most people sit on furniture and radiant goes in straight lines from emitter to the heat sink (the occupant). The heat is coming out of the tubes through some floor mass with an associated R value and then into the bottom of the couch and then ultimately into the occupant. This is a slow process compared to convective heating. He advocates that installing radiant tubing behind a wall or a ceiling with insulation behind and drywall on top allows a direct line of radiant heat from the wall to the person and skips the floor and the furniture. This is a much faster response time and there is far better chance that the heating load can be varied over the course of the day dependent on usage. This backs up John's underlying design concept that every space in the structure should be individually zoned or equipped with local controls so that the amount of heat can be varied with usage. Basically heat the space where the occupants are versus where they might be at some point in the future.

There is also the issue that the best efficiency of heating system is to run the distribution temperature as low as possible. To a wood boiler with storage owner that means that for given volume of storage, the lower the outlet temp before the tank needs recharge the larger the thermal capacity of the storage . Alternatively the storage can be run at a lower upper temp to reduce standby losses as well as losses in the piping on its run to the point of demand. The staple up systems and floor systems require higher distribution temps for the same heat output than a radiant wall panel if the temperature is being cycled to usage.

Where the radiant floors seem to excel are for garages or public spaces like churches that have a lot of floor space compared to wall space with high ceilings. Radiant in the floor means that the air temp can be kept low with the equipment being kept warm by the heat radiated from the floor. Convective type air flow works less well as the heat doesn't get to the floor unless its circulated so the entire space has to be heated to a higher temp. I am quite familiar with this when working on equipment that it can be T shirt conditions walking around but really cold when under the equipment. It is also a nice option in a mud room as the temp doesn't have to be kept as high but the radiant heat helps to evaporate any water and also dry boots. As mentioned in bathrooms, its also nice as folks tend to have bare feet and there are lot of obstructions to install radiant wall panels plus more difficult to clean. I expect radiant tubing in the walls and ceiling would also work but not as well as imbedded radiant.

Realistically many of the new net zero Passivhaus/Pretty Good House designs use so little heat that they only install space heaters as backup and usually dispense with hydronic systems. If the heating load is low they are far better off spending the money normally spent on a chimney/wood boiler/storage /controls /distribution system on PV panels with net metering. They then use spot electric heaters and minisplits and I expect more than few of these houses end up with some electric radiant in the bathroom floor. Some compromise and install a very small woodstove to cover them in case of loss of utility. I realize this is tough for most folks to get their head wrapped around but by building a structure right to begin with the energy required to heat it is minimal even in northern climates.

 

[Bad LP]

Peakbagger made some very good points. RFH is very slow to respond to changes in temperature. So slow in fact that major swings in set temps are a waste of time. I haven't bothered to try small changes with a programmable thermostat because I'm only in the house weekends at this point in life. That said there is a lot to love about warm floors and walking around in your socks when its 0 outside. Not sure how to protect tubing installed in the walls from picture hooks. That's going to need a lot of protection. I've been told to ask any bald headed guy about radiant heat in a ceiling. They don't like it.

I'm lucky in a way because I zoned all of the second floor rooms. I will be removing the HWBB this spring and installing panels. These of course will have programmable t'stats to take full advantage of not being in the bedrooms during the day. I do wish I had the opportunity for a towel bar radiator in addition to the heated bathroom floors but there's no way that's going to happen now.

 

[mark123]

I'm getting ready to build a new house in the spring. I hope to have a Varmebaronen Vedolux 650 boiler with radiant floor heat. How should I install the radiant floor? Is there a difference in efficiency or cost between laying it in gypcrete, in a wood track system, or under the sub-floor between the joists? Is there any value to putting it between the joists so you can access the piping in the future?

I built a new house 10 years ago and have a Woodgun 180. I used open web floor joists with radiant pex piping nailed on approx 3" below floor. 1 row on each side of every joist. R20 fiberglass batts towards bottom of joists then drywall for basement ceiling. At first with mixing valve only supplying tempered water it wasn't effective at all. I then turned mixing valve as to supply full hot water sometimes 200 degrees C . 10 years later it is still working great. This is also feeding the in floor pex in basement and garage concrete floors. No cracks and nice warm floors throughout the house. I have 5 zones all on digital thermostats, it took some trial and error with the on off cycles so the house wasn't too hot but it is great now.

 

[peakbagger]

I've been told to ask any bald headed guy about radiant heat in a ceiling. They don't like it. I am just about on the edge of qualifying to comment I think the issue with any heating system is how well the space is insulated. In ceiling radiant was quite popular at one point but that was on houses built to a far lower energy standard. I expect the old systems really had to crank out the BTUs which meant high supply temperatures to make up for heat loss through marginally insulated walls, concrete slabs and single pane windows. I know of at least one person who went with wall and ceiling radiant in a kitchen addition and was quite happy. Since the typical room is much tighter now, I expect the supply temps are far lower thus making it less of issue with those who are follicle challenged. The picture hanger issue is just matter of common sense, use a stud finder and put the nails in the studs.

As an aside I remember my dad wanting to install 6" insulation in the walls when we finished a second floor space around 1970, the building supply stores had to special order anything thicker than 3.5" and the standard recommendation was not to go anything thicker as we would rot out the walls. Many walls of that era used 2" or less and in more southern areas they used none. If energy was cheap why spend the money to insulate?

 

[Mike Fromme]

For retrofits I can see it being more cost effective to do in wall or ceiling... Lot easier to lower the ceiling an inch or two in some rooms then to raise the floor. For walls it's easy enough to cut out and patch a section from the top of the baseboard up 4' or so. Or you could surface mount the tubes on a wall and incorporate wainscoting to cover them up.

 

[Bad LP]

I've been told to ask any bald headed guy about radiant heat in a ceiling. They don't like it. I am just about on the edge of qualifying to comment I think the issue with any heating system is how well the space is insulated. In ceiling radiant was quite popular at one point but that was on houses built to a far lower energy standard. I expect the old systems really had to crank out the BTUs which meant high supply temperatures to make up for heat loss through marginally insulated walls, concrete slabs and single pane windows. I know of at least one person who went with wall and ceiling radiant in a kitchen addition and was quite happy. Since the typical room is much tighter now, I expect the supply temps are far lower thus making it less of issue with those who are follicle challenged. The picture hanger issue is just matter of common sense, use a stud finder and put the nails in the studs.

As an aside I remember my dad wanting to install 6" insulation in the walls when we finished a second floor space around 1970, the building supply stores had to special order anything thicker than 3.5" and the standard recommendation was not to go anything thicker as we would rot out the walls. Many walls of that era used 2" or less and in more southern areas they used none. If energy was cheap why spend the money to insulate?

We were looking at a house design that had a ton of glass (50% glass) in the living room alone, 2 stories high. It was going to need pex in the walls to overcome the loss. I've heard of people heating the countertops in the kitchen to get more surface area but I'm not too keen on that thought. In hind sight our own kitchen is cooler due to being on the north side of the house, 3 cold walls and half the ceiling has unheated (outdoors) space above it. Thankfully there is so much pex in the floor that it was real easy to isolate that area and turn it into its own zone. I added an electric toe space heater at first but don't care much for the noise.

I remodeled a 1970's house a few years back that had electric radiant heat in the ceiling. Of course it was eliminated and a FHA system was installed before it went on the market. I'll bet you could have cut cord wood on the electric meter

Back in the mid/late 60's I remember watching my father roll out fiberglass in the attic of their first house. (He was an engineer) When they bought a larger house in the early 70's the very first thing he did was add more insulation the attic.

 

[Kelster]

Kelster, what is your opinion on using a basement slab to act as heat storage?

If my slab is heated with say 120* water should I then turn off my circ pump and wait until I have used the heat from my boiler for the main floor before turning the slab pump back on again to circulate that water through my system?

Or what is the best way to use a slab for storage?

Hey Woodfarmer,
You can approach this in several ways but at the end of the day, it's whatever works best for you. If your slab is heated sufficiently (to a comfortable temperature, whatever that is), then your boiler energy can redirected elsewhere and if those zones are satisfied then your boiler should cycle-off based on the setpoint at the boiler. You can have a fully automated system or you can keep an eye on the dog to see if he/she is panting excessively

Your slab is an ideal storage medium, so take advantage of it.

KB

 

[Kelster]

I took a heating course last year on line taught by John Siegenthaler the generally acknowledged expert on residential and small commercial heating. He covered floor based radiant systems along with many other methods and uses it in selected places in his designs but he was actually a lot more of a advocate for other methods like radiant wall panel heaters located along the exterior walls and embedded wall and ceiling radiant systems. This is probably heresy to radiant floor owners who were brought up on steady diet of This Old House reruns but John had some very good reasons for this. Realistically I am not going to condense a 3 month course in an internet post but be aware that radiant floor is an important tool in a quiver of many approaches and it may not be the best fit if you want the best efficiency. Sure consider it in bathroom and an entryway but in others areas it is an expensive way to go and inherently is not the most energy efficient.

The primary issue is thermal mass and the slow response of radiant floors. The poured in systems have lot of mass and they end up being set and forget. Adjusting the output for daily usage just doesn't work very well as they take a long time to respond to a request for temperature change. This means the room is left at the highest temp required at one point in the day 24/7 whether occupied or not. This may be a good tradeoff for a small bathroom where the warm floor for 5 to 15 minutes a day is worth it to the owner, but that is a comfort decision version versus energy efficiency. The staple up tubing systems also have an issue that unless the floor coverings are optimized, the heat has a tough time getting to where its needed. This design also has a slow response time and the supply temps end up having to be higher than in other options. Most people sit on furniture and radiant goes in straight lines from emitter to the heat sink (the occupant). The heat is coming out of the tubes through some floor mass with an associated R value and then into the bottom of the couch and then ultimately into the occupant. This is a slow process compared to convective heating. He advocates that installing radiant tubing behind a wall or a ceiling with insulation behind and drywall on top allows a direct line of radiant heat from the wall to the person and skips the floor and the furniture. This is a much faster response time and there is far better chance that the heating load can be varied over the course of the day dependent on usage. This backs up John's underlying design concept that every space in the structure should be individually zoned or equipped with local controls so that the amount of heat can be varied with usage. Basically heat the space where the occupants are versus where they might be at some point in the future.

There is also the issue that the best efficiency of heating system is to run the distribution temperature as low as possible. To a wood boiler with storage owner that means that for given volume of storage, the lower the outlet temp before the tank needs recharge the larger the thermal capacity of the storage . Alternatively the storage can be run at a lower upper temp to reduce standby losses as well as losses in the piping on its run to the point of demand. The staple up systems and floor systems require higher distribution temps for the same heat output than a radiant wall panel if the temperature is being cycled to usage.

Where the radiant floors seem to excel are for garages or public spaces like churches that have a lot of floor space compared to wall space with high ceilings. Radiant in the floor means that the air temp can be kept low with the equipment being kept warm by the heat radiated from the floor. Convective type air flow works less well as the heat doesn't get to the floor unless its circulated so the entire space has to be heated to a higher temp. I am quite familiar with this when working on equipment that it can be T shirt conditions walking around but really cold when under the equipment. It is also a nice option in a mud room as the temp doesn't have to be kept as high but the radiant heat helps to evaporate any water and also dry boots. As mentioned in bathrooms, its also nice as folks tend to have bare feet and there are lot of obstructions to install radiant wall panels plus more difficult to clean. I expect radiant tubing in the walls and ceiling would also work but not as well as imbedded radiant.

Realistically many of the new net zero Passivhaus/Pretty Good House designs use so little heat that they only install space heaters as backup and usually dispense with hydronic systems. If the heating load is low they are far better off spending the money normally spent on a chimney/wood boiler/storage /controls /distribution system on PV panels with net metering. They then use spot electric heaters and minisplits and I expect more than few of these houses end up with some electric radiant in the bathroom floor. Some compromise and install a very small woodstove to cover them in case of loss of utility. I realize this is tough for most folks to get their head wrapped around but by building a structure right to begin with the energy required to heat it is minimal even in northern climates.

Hey Peakbagger,
I'm envious of your session with John Siegenthaler. I've been looking at taking that online course as well but find the cost to be prohibitive.

He's correct that radiant ceiling and wall panels are gaining in popularity. I sell radiant panels but by far the market for Ceiling mounted panels accounts for the bulk of the radiant panel business. It's basically an extruded aluminum panel with 1/2" copper tube bonded to the backside of the panel. Very popular in perimeter zones for commercial offices, schools and health care, but I have yet to see that trend extend to residential, which is probably due to the comfort level of residential designers and trades people. Having said that, you can't argue with more Mass which is the huge advantage that in-slab radiant brings to the table and even the best in-wall or ceiling systems will never replace in-slab (imho).

I agree with John's concept of 'zone every room' and that's the ideal but at what cost?

Netzero / Passivhaus designs are whole nother kettle of fish. Heating a house with light-bulb sounds great but how many of us can really afford to build a house of that type. I expect the cost will come down over time when North American manufacturer's get on board and we don't have to import building materials like wood fibre insulation from the EU.

My 2bits.

 

[peakbagger]

I don't advocate for Passivhaus, I recommend the folks in Vermonts's Pretty Good House concept http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/pretty-good-house. They se standard materials and get 90% of the benefits for far less cost.

John advocates local control valves direct mounted on the radiant panels for each room versus a full out zone. The home run designs off a manifold are nice but pricey.

 

[Fred61]

The problem with using a concrete slab as storage is that the concrete doesn't readily absorb the heat like water does and is nearly un retrievable using the method you want to use. Water flowing through pex doesn't absorb the heat from the concrete at a fast enough rate to make it worth your while to install any mechanicals to do it.

The best way to retrieve heat from a concrete slab is going to happen naturally and that is stratification. The warm slab will radiate enough heat to make your house think it lives 150 to 200 miles further south than where it is actually located. It reduces the load on the upstairs zones.

Kelster, what is your opinion on using a basement slab to act as heat storage?

If my slab is heated with say 120* water should I then turn off my circ pump and wait until I have used the heat from my boiler for the main floor before turning the slab pump back on again to circulate that water through my system?

Or what is the best way to use a slab for storage?

 

[Woodfarmer1]

That's the answer I was looking for Fred, as that has been my experiance.
My system was the same as Mark123's except I had to add two stelrad's in my great room as the I floor radiant wasn't up to the task.

 

[Bob Rohr]

The very best first step is a room by room heat load calculation. Once you know the heat load of each room you can determine if radiant is workable. free online calculators from SlantFin and US Boiler.

The more wood and flooring above the radiant tube the higher the operating temperature required. Generally radiant floors should not run above 80- 83 surface temperature or they become very uncomfortable to stand on.

In some cases the floor area is not sufficient to cover the heat load, and additional heat is required. The RPA suggest 20- 25 BTU/ square foot is reasonable. Beyond that you end up with excessive temperatures at the floor.

A rule of thumb is 2 btu/ square foot temperature difference.

So a floor temperature of 82 in a room with 70 ambient would be 12X2= 24 BTU/ square foot.

Radiant walls or ceilings could run 90- 100 as you don't generally stand on them, so much higher output per radiant surface area.

Radiant floors in a bath and kitchen where most standing is done. Radiant walls or ceiling, or panel radiators for additional areas are my choice. Those are quick responding and easy to retrofit.

I like panel rads in sleeping areas as they are easy to zone with TRV valves and can be set back for room by room temperature control

 

[Woodfarmer1]

What's the best way to extract more heat, reduce the flow and speed of pumps or increase flow rate?

 

[Kelster]

What's the best way to extract more heat, reduce the flow and speed of pumps or increase flow rate?

The best way to extract more heat is to add more heat transfer surface area. Varying the flow rate up/down will only change the temperature difference in the fluid:
Qbtuh = GPM x TD x 500 (assuming no glycol)

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