Radiant Floor Heat in Bathroom and other ramblings...

[Larry Peterson]

Hi All,
We recently finished an addition and whole house remodel. We opted for a tile floor in our new bathroom.
Initially we were interested in doing electrical radiant heat in the bathroom but our contractor convinced us we would be better off with tying in a radiant heating zone on our new propane furnace.

Now that the weather has stayed cold for a couple months here in Massachusetts, we are finding out a few things we werent expecting.
1. Propane is costing us a fortune. $200 every 2-3 weeks.
2. The radiant heating in our bathroom will never reach its setpoint if the rest of the house is set below its setpoint. Even when the house is warmer than the bathroom setpoint, the bathroom zone is on far more than it is off. We have tried keeping the doors shut to the bathroom but it doesnt seem to make a difference.
We have a wall mounted honeywell standard thermostat

on the wall about 5' off of the floor. The floor has 2 layers of 1/2" plywood, a layer of durarock and then the porcelain tile on top of that. The floor joists below are on 16" centers with one loop (2 lines) in each of the 6 bays. I insulated each bay with the foil backed insulation and tried as best i could to keep a 2" air gap where i could. I then put in some R15 non faced insulation bats as shown in the photos.
The zone feeding the radiant heat runs at about 120 degrees when its calling for heat.

So my questions are as follows.
1. Is there just too much mass to heat?
2. Should i have used a different thermostat with a thermocouple located on or near the floor?
3. There is only R15 insulation above this bathroom in the attic. I just went out today and picked up 27 rolls of R30 unfaced fiberglass insulation and ill be installing all of that tomorrow in the attic above the original part of the house. I did have a double layer of R15 up there but a lot of it got trashed during the remodel. Some areas, particularly the area above the bathroom will end up with the 2 layers of the R15 and one layer of the R30 when all is said and done tomorrow. I dont expect all that to change the issues im having in the bathroom that drastically. I do hope that itll help cut down on the heating costs overall as a single layer of R15 just isnt sufficient.
4. How critical is it to have the 2" air gap between the reflective insulation and the radiant lines?
5. Should i consider raising the temp up another 10 degrees to 130 degrees? This seems like a bandaid approach and that there is some other bigger issue here.
6. In the attached pictures, you can see where the plumber ran the lines under the floor joists and into the next bay. Should there have been holes drilled through the floor joists and the lines ran through them?
Would that have made much of a difference?
7. I read about the use of heat exchanger plates. Is that easy enough to do after the fact and would they make that much of a difference?

Any help would be appreciated.

 

[Jadnashua]

How is the pex attached to the flooring? If it is just hanging there without any contact, or if in contact, it doesn't have a metal (usually aluminum) panel to help distribute the heat, I'm not surprised you're not getting good results...120-degree water in pex without a good means to distribute it (intimate contact, ideally with a good thermal conductor) just will not distribute much heat. Even if an edge is stapled up against the subflooring, the conductive heat transfer will be minimal, especially at those distribution temperatures. You won't get much convective heating, either, as I doubt that the joist bays are all that well air sealed.

 

[Sponsor]

 

[Larry Peterson]

Jim,
The PEX is attached using similar (but open) clips as shown in the pictures i attached. The clips are open on one side allowing the PEX to be in contact with the sub floor. So with that said am i looking at the need to invest in some of the aluminum plates? I did some research on them and it appears the extruded ones are a little thicker and seem to be the preferred ones to use for this type of application. The contractor doubled up on the floor joists, so my spacing in the bays varies. 1 bay is at 11", 1 at 15" and the rest are around 13". I see there are 4" and 5" widely available with 2' and 4' lengths being pretty common. The PEX runs parallel with the floor joists and about 2" off each one. I see there are 3 primary extrusions available. U, Omega and C referring to the channel that the PEX sits in.
It seems to me the U or Omega would be the preferred and offer more contact area with the PEX. Im thinking 4" instead of 5" just so i dont risk kinking or bending the radius at the ends of the bays. Are there some better places to purchase the extrusions from?

 

[WorthFlorida]

Is your foil back insulation similar to Reflectix? Reflectix or similar product is not an insulator but to reflected the radiant heat back toward the floor.
What type of furnace you have to heat the water? When you're circulating the heated water and not much of the heated is given off, then the water temperature back to the furnace would be high and not needing much more heat to get it to temperature. If your furnace stores water it would cycle on and off to maintain the temperature if the circular pump was running or not. Other than the cost of the electric to run the pump and you have no energy leaks, your propane bill may be higher if all that heated energy was getting into the room.

I searched on line and it seems 130 degree is the max recommended temper for floor radiant heating to protect the wood flooring material especially for hardwood finished floors. I would turn up the water temp up to 140 degrees and give it a try for a few hours and see how it works. If it improves then lowered down to 130 degrees and check it again.

http://www.homedepot.com/p/Reflecti...-Insulation-with-Staple-Tab-ST16100/202851859

 

[Larry Peterson]

Is your foil back insulation similar to Reflectix? Reflectix or similar product is not an insulator but to reflected the radiant heat back toward the floor.
What type of furnace you have to heat the water? When you're circulating the heated water and not much of the heated is given off, then the water temperature back to the furnace would be high and not needing much more heat to get it to temperature. If your furnace stores water it would cycle on and off to maintain the temperature if the circular pump was running or not. Other than the cost of the electric to run the pump and you have no energy leaks, your propane bill may be higher if all that heated energy was getting into the room.

I searched on line and it seems 130 degree is the max recommended temper for floor radiant heating to protect the wood flooring material especially for hardwood finished floors. I would turn up the water temp up to 140 degrees and give it a try for a few hours and see how it works. If it improves then lowered down to 130 degrees and check it again.

http://www.homedepot.com/p/Reflecti...-Insulation-with-Staple-Tab-ST16100/202851859

I did use the Reflectix material you linked to and then put the R15 insulation up after. The furnace is a Weil Mclain WM97+ propane furnace.
I see your point about the return water temps and the furnace not having to run as often. This might not be as big a culprit in our high propane use but the issue with it not heating the room still remains. I shut off the bathroom thermostat yesterday morning and left both bathroom doors open. The bathroom can be entered from the hallway as well as a door off of our Master Bedroom. With both doors left open, the thermostat reads the same as the setpoint for the upstairs thermostat. We will see in a few weeks if the combination of shutting off the bathroom thermostat and adding the R30 insulation to the entire attic has cut our propane bill.

I sent away for a free sample of this aluminum extrusion from Radiant Engineering. http://radiantengineering.com/tfinc
Still open to suggestions on other suppliers. Not sure of the cost on the Thermofin C product they sell, so no idea what itll cost to do the 6 bays.

We also have a superstore water tank that runs off of the furnace, so that could be adding to the excessive propane use. Although i was assured that with only 2 people living in the house, that the superstore wouldnt run that often. I need to look into that and see if the Weil Mclain furnace has a runtime log. We also have a propane stove but that doesnt get that much use either.

The new addition has vaulted ceilings with trapezoidal windows and 9' long windows, so there is a lot of glass. Highly energy efficient Marvin Integrity windows and doors but still a lot of glass. Seems to help keep the house warm during the day but not as insulated as a 2x6 wall with R21 insulation in it. Square footage of the house is 2800.
Maybe $200 every couple of weeks is our new norm for this size house with the furnace running heat, hot water and stove but its a tough pill to swallow.

 

[WorthFlorida]

Reading around, floor radiant heating can be subject to air blocks just like any other hydronic system. I remember well that each year my dad and I would open a valve at each radiator to purge out any air. You can add a valve at the far end of the your system to do just that. Once a year open it up with the pump running to flush it and purge any air. This probably is not be your present problem. As Jim suggest PEX doesn't transfer heat very well and two layers of plywood also does not transfer heat very well either, plus the mass of the Durarock and tile before it heats the air in the room. I would be curious what is the air temperature in the cavity between the foil and the floor? Does the tile floor ever feel warm?

 

[Jadnashua]

I don't have any personal experience with selecting the radiant aluminum channels...maybe someone else has. The trick may be getting them up there without damaging the flooring on top. A staple gun may help. See what others may suggest. You want the metal in as intimate contact with the bottom of the subflooring as you can get. The thinner panels may end up a little warped.

A radiant barrier requires an air gap to work, otherwise, it acts just like a conductor. It usually calls for a minimum of 1/2" air space. If there is any air movement at the ends of the joist bays, without conduction, the convection won't transfer much heat as it will just blow away out the ends. Fiberglass isn't the greatest insulator if there's any air infiltration...it acts more like a big air filter!

If you have one, or can borrow one, an infrared thermometer or a FLIR will allow you to see how well the heat is distributed across the floor, and may also help diagnose where that heat is going.

If your radiant piping has a supply and return water temperature gauge set, check what your supply and return temperatures are and let us know. If not, it's a good measure to install them. If you can feel the supply and return lines near the manifold, do you notice much difference between the two sides? If more than one zone, differences between the zones?

YOu can find the energy content of propane, and compare your use to the heating degree days for the period in question to first see how many actual BTU's your using, and then assess how efficient your setup is. There can be a huge difference in cost for heating the indirect based on user preferences...there's a big difference between a 5-minute shower with a single head verses 30-minutes with multiple ones! IOW, it's hard to say what size and the cost needed to supply your hot water just based on the number of people in the house! Throw in how often you wash clothes, dishes, and other things, it may or may not be a significant portion of the energy usage. Last, in most places, propane may be about the most expensive fuel choice. It may be your only one (well, electricity can be worse depending).

 

[WorthFlorida]

You really cant't get any better than a tankless system for efficiency. It does seem that your heating needs really jumped with the remodel. Do you have any ceiling fans to push down the excess heat at the ceiling?

Check with your electric company web site. Some of them will have charts with fuel comparison and cost since they usually want to push electric usage where they know other fuels are more costly.

My brother has a two story log home in Vermont (weekend retreat) and heats with a tankless system and propane. No problem with heating except the bill for the propane. Two years ago he installed one of those stoves on the lower level that burn paper pellets. It really gives off a amazing amount of heat and it is computer controlled. The unit at the time was about $1400 and he buys the fuel pellets by the pallet from the local hardware store. No Home Depot's in West Dover. Something you might look into for the future.

http://www.exothink.com/Pages/btu.html
BTU Content of Common Fuels

Electricity BTU's
1 KW/hr 3,413
OIL BTU's
1 Gal. #1 Fuel 136,000
1 Gal. #2 Fuel 138,500
1 Gal. #3 Fuel 141,000
1 Gal. #5 Fuel 148,500
1 Gal. #6 Fuel 152,000
Gas BTU's
1 lb. of Butane 21,300
1 Gal. of Butane 102,600
1 Cu. Ft. of Butane 3,260
1 Cu. Ft. of Manufactured Gas 530
1 Cu. Ft. of Mixed Gas 850
1 Cu. Ft. of Natural Gas 1,075
1 lb. of Propane 21,600
1 Gal. of Propane 91,000
1 Cu. Ft. of Propane 2,570

 

[Larry Peterson]

Thanks for the replys guys. The floor does heat up if i set the Tstat high enough and let it run continuously. I got the quote back from Radiant Engineering and it looks like 1 box of the heavier extruded aluminum plates would be about $168 plus shipping. It comes in 20 4' long pieces and i need about 72'.

There is no return temp gauge but i could probably rig something up and attach it to the garden hose fitting for the drain port.
I knew going in that propane would be a little more expensive but thought the higher efficiency furnace would have made up for some of that.
That and conversations with friends and 2 plumbers convinced me to go the propane route.

We did and are looking into a pellet stove as a supplemental heat source but in these parts you need both an air intake and exhaust pipe ran to the stove. I have a woodstove in the basement but its getting old and is a pain to keep going. The pellet stove would probably replace it. Pellets aren't cheap either, so the pellet thing is going to have to wait until the money situation improves.

It would be great if someone else could provide some feedback as to how much of an improvement i should see using the extruded aluminum plates and if that seems like a good price for 80' of it.

 

[Dana]

Terminology: A "furnace" is not a boiler. What you have is a boiler, not a furnace. The heat delivery fluid of a space heating furnace is air, not water.

A temp of 120F is pretty low for a no-plate staple-up, but there isn't a significant efficiency hit to just bumping up the water temp of a condensing propane boiler to 125F-out (or even 130F) which will be cheaper and easier (and more tweakable) than heat transfer plates. But let's not get ahead of ourselves here- I'm not quite understanding your system.

Is the bathroom it's own micro-zone, or just one room among others on a low temp 120F water zone?

Propane in MA is ridiculously expensive at about $3/gallon (this week's pricing). Burned in a 95% efficiency boiler a gallon of propane delivers about 0.95 x 91,500= 87,000 BTU/gallon. Normalizing to $ per million BTU (MMBTU) that's (1,000,000/87,000=) 11.5 gallons/MMBTU, which at $3/gallon costs ~ $34.50/MMBTU, (plus pumping power used.)

At kwh of electricity in a resistance heater delivers 3412 BTU. So it takes (1,000,000/3412= ) 293 kwh/MMBTU. At 20 cents/kwh (typical pricing from large utilities in MA, say National Grid or Eversource) and normalizing to $/MMBTU that's $58.60/MMBTU, which is quite a bit more expensive than propane. If you're on one of the cheaper small municipal systems with 12 cent/kwh (all-in) retail power it would be at rough cost parity with $3 propane.

As far as auxiliary heat goes, a ductless mini-split may end up being cheaper heat than pellet fuels ( $15-20/MMBTU with 20 cent electricity, $10-12 with 12 cent electricity) and would be able to deliver high efficiency air conditioning as well as heating. At $250 per ton the source-fuel heat of the pellet stove runs ~$15-18/MMBTU, and even at 85% efficiency (brand new EPA better-class stove) would be about $18-21/MMBTU. Current pricing in MA is $257/ton delivered in bulk, but closer to $300/ton bagged. Between the PITA factor of storing & managing bulk-fuels, the local air pollution issues and the potentially differences in operating cost, the marginally higher initial cost of installing a decent quality cold-climate mini-split is probably "worth it".

A wood stove in a below-grade basement doesn't meet current IRC code, since the air inlet to the house/room is higher than the firebox, making it more prone to backdrafting. Being forced draft, a pellet stove wouldn't have that issue.

 

[Larry Peterson]

Terminology: A "furnace" is not a boiler. What you have is a boiler, not a furnace. The heat delivery fluid of a space heating furnace is air, not water.

A temp of 120F is pretty low for a no-plate staple-up, but there isn't a significant efficiency hit to just bumping up the water temp of a condensing propane boiler to 125F-out (or even 130F) which will be cheaper and easier (and more tweakable) than heat transfer plates. But let's not get ahead of ourselves here- I'm not quite understanding your system.

Is the bathroom it's own micro-zone, or just one room among others on a low temp 120F water zone?

Propane in MA is ridiculously expensive at about $3/gallon (this week's pricing). Burned in a 95% efficiency boiler a gallon of propane delivers about 0.95 x 91,500= 87,000 BTU/gallon. Normalizing to $ per million BTU (MMBTU) that's (1,000,000/87,000=) 11.5 gallons/MMBTU, which at $3/gallon costs ~ $34.50/MMBTU, (plus pumping power used.)

At kwh of electricity in a resistance heater delivers 3412 BTU. So it takes (1,000,000/3412= ) 293 kwh/MMBTU. At 20 cents/kwh (typical pricing from large utilities in MA, say National Grid or Eversource) and normalizing to $/MMBTU that's $58.60/MMBTU, which is quite a bit more expensive than propane. If you're on one of the cheaper small municipal systems with 12 cent/kwh (all-in) retail power it would be at rough cost parity with $3 propane.

As far as auxiliary heat goes, a ductless mini-split may end up being cheaper heat than pellet fuels ( $15-20/MMBTU with 20 cent electricity, $10-12 with 12 cent electricity) and would be able to deliver high efficiency air conditioning as well as heating. At $250 per ton the source-fuel heat of the pellet stove runs ~$15-18/MMBTU, and even at 85% efficiency (brand new EPA better-class stove) would be about $18-21/MMBTU. Current pricing in MA is $257/ton delivered in bulk, but closer to $300/ton bagged. Between the PITA factor of storing & managing bulk-fuels, the local air pollution issues and the potentially differences in operating cost, the marginally higher initial cost of installing a decent quality cold-climate mini-split is probably "worth it".

A wood stove in a below-grade basement doesn't meet current IRC code, since the air inlet to the house/room is higher than the firebox, making it more prone to backdrafting. Being forced draft, a pellet stove wouldn't have that issue.

Dana,
A lot of good info and thank you. The bathroom is on its own zone and is the only radiant heating in the house. All the rest of the house is fin baseboard heat. Their are 4 zones on the boiler. The primary being the super store, the upstairs, downstairs and then the bathroom.
Our most recent propane bill was $2.41/gal.

We had our eyes on a ductless system for AC but ran into some major overuns during the remodeling and that was one of the first things to go.
Honestly i wasnt even aware that those systems could be used for heat. My most recent electric bill was $108.00. KWH used was 683. Cost pr/KHW is almost .16 cents. We are on a town run municipal electric service and our rate is usually higher than most others.

Our addition is split down the middle with 1/2 being the new Master Bedroom and the other 1/2 the new living room. Both rooms have 13 foot vaulted ceilings. Looks like there are multirroom Ductless splits. I agree that dealing with pellets isnt something we have the room or patience for.
Id much rather invest in the ductless system and have the added benefit of AC in the summer. I dont see us getting into a system like that for anything less than $5-7K

Right now though id just like to get the radiant heat working in the bathroom. Why do you say adjusting temps on the radiant zone would be more tweakable than using heat transfer plates? Cheaper and easier yes but i would think the transfer plates would only help and that i could still tweak the supply temp.

 

[Dana]

If you use extruded heat transfer plates you'll likely have to tweak the temperatures DOWN.

Let's go to first principles, and actually take a stab at DESIGNING (at least at a napkin-math level) a solution rather than wasting time & money hacking. It starts with a heat load calculation.

How many square feet of exterior wall, and what is the material stackup from the outdoor paint/siding to the interior finish paint/tile whatever (including insulation R-values) ?

How many square feet of attic or cathedralized ceiling, and what is that material stackup (including insulation)?

How many square feet of window, and what is the manufacturer's published U-factor for the window?

What is your ZIP code? (Needed for 99% outside design temperature purposes.)

Then..

How many square feet of exposed radiant floor (not under tubs, toilets or cabinets, etc.)?

What is the tubing size? (Half-inch PEX is typical, but 3/8" and 3/4" are also used in staple-ups like this.

Is the boiler operating at a fixed 120F, or is it operating under outdoor reset control?

BTW: Microzoning low-mass radiation like staple-up is prone to short-cycling the hell out of the boiler on zone calls, and you may want to combine zones, since bathroom loads tend to be quite small. The problem is outlined at the napkin-math detail this bit o' bloggery. What boiler model/make boiler do you have?

Also, with an inch of plywood (about R1.2-R1.5) between the tubing and Durarock the time lag and high/low temp hysteresis for staple-up radiant floors is way too long for the built in anticipation of most standard thermostats to manage well, and adding heat transfer plates won't fix that (much) . The inappropriate thermostat is likely a major part of the problem, since you report that if you crank it up to where it runs continously, the floor eventually warms up. Depending on the calculated heat load may be better off with just a floor thermostat, which would be cheaper and possibly more effective than extruded heat transfer plates. If you the floor to 73-75F and forget it for the winter. The room temps might vary from 68F to 75F, but it'll never be uncomfortable.

Regarding ductless heating, a typical cold climate 3/4 ton mini-split can deliver over 10,000 BTU/hr @ +5F (Worcester's 99% outside design temp), and comes in at about $3K in competitive bidding. A 1-ton is good for about 15 KBTU/hr @ +5F and runs between $3.5-4K in competitive bidding. A 1.25 tonner would run about $4-4.5K. A pair of 1.25 tonners would have more capacity than the heat load of my whole house, a 1920s 2x4 framed antique with clear-glass storm windows. As auxiliary heat you would use it like a pellet stove, point source heating in a larger more open space.

Multi-split systems tend to be less efficient and more expensive than individual multi-splits, and the common mistake of installing one head per room is usually an efficiency disaster due to extreme oversizing for the whole-house load. It's better to take a look at the rooms/zones you care about the most, and run an aggressive Manual-J load calculation on those rooms, at both the 99% outside design temp, but also at +47F. The efficiency of the systems in heating mode are tested at +47F, and the test includes determining the minimum-modulated output at +47F. Ideally the mini-split would have a minimum output @ +47 that is smaller than the room/zone's heat load at that temperature, yet still have sufficient capacity to cover the load at the 99% outside design temp.

In this climate sizing for the heat load is far more important than sizing for the cooling load, but in extreme cases (a lot of unshaded "sunset view" west facing glass) the peak cooling loads can sometimes exceed the peak heat loads.

If you have a heating history on this place uncontaminated by wood-burning (where the source fuel BTU & efficiency vary by quite a bit), it's possible to put an upper bound on the whole house heat load based correlating propane use against heating degree-day data for your location using this methodology.

 

[Larry Peterson]

Dana,
Thats a lot of info i dont readily have. Ill work on this over the next couple days and get back to you.