heat for master bath

mwalsh3

I just finished renovating my master bath (live outside Boston) which is about 6' x 10' in size. I currently do not have any heat in the room (small oversight!), but it's actually pretty comfortable as long as I leave the door to the bedroom open. My wife doesn't share this opinion, however, so I'm trying to figure out the best option to add some heat. I have a 10 yr old FHW system in the house with the loop from the old bath capped off in the basement (which is completely open). Reinstallling a baseboard isn't a great option as I don't have a lot of open wall space with the new design the baseboard Some options that I've considered:



1) electric wall heater which is easy to install, low initial cost but might get expensive to run through a cold winter?



2) runtal towel warmer. Could use electric (which I can install) or hydronic (need to get a plumber), doubles as a towel warmer but cost is high



3) install radiant floor heat in the joist bays. My bath floor is tile over 1/2" CBU over 1/2" plywood over 3/4" planks and I have easy access from my basement. I don't know much about this option (can I connect to the old FHW llop, cost of install)?



Any thoughts or suggestions?



Thanks,

Mike

Brad White

Door Number Three

Depending on your heat loss, in fact, I will come right out and say it, you are not likely to heat your entire bathroom by radiant floor alone. But given the easy access, I would do it just because you can!



The factors that are working against you are the relatively high resistance between tubing and tile, about R-2. The other drag on this is the useful area available. Even if you "radiate" the entire floor footprint, what is under the tub and vanity will not be as useful to you as open floor. 



What is working for you is the easy access. In fact, a hydronic towel warmer combined with the radiant may do it, if calculations support it.  If you can do the radiant floor, installing a towel warmer is easily within reach. Warm floors and warm towels are a wonderful thing. The other thing that is working for you is that leaving the door open between uses helps a lot. It also says that your heat loss is not insurmountable. Regardless, it has to be calculated.  But if you go that route, use extruded aluminum plates and insulate well underneath the floor once you are done.



As for cost of installation, we do not discuss pricing here.

I am not an installer, (except for myself),  but do live outside Boston myself, Newton by the way.



My $0.02



Brad

mwalsh3

calculations

thanks for the quick reply.

How do I go about calculating if the radiant (and maybe towel warmer) will be enough for this room?

Steamhead

You would have to use

a heat-loss calculation program geared toward radiant. I think Watts Radiant might have a free version of this.



Also consider operating cost. Electric heat has the highest cost per BTU in most parts of the country, unless you live in an area with a lot of hydro such as TVA or the Pacific Northwest. This will drastically increase your utility bills.

hot_rod

Have it both ways

I have in slab radiant in the bathroom. Nothing beats a warm, dry bathroom floor. I added a Runtal electric towel bar also. I use that in the shoulder seasons, as the heat, before the wood or LP boiler are fired up.



I have it on a timer and thermostat so it can start up an hour before we get up, and for showers in the evening. You can fine tune the output by adjusting the amount of "towel" you put onboard. It warms much more quickly then waiting for the floor "'flywheel" to rev up and belch warmth.



hr

Alan (California Radiant) Forbes

If money grew on trees.......

I would heat the floor using PEX tubing and aluminum plates AND have a Runtal hydronic towel warmer.  The floor heat would somehow have a floor sensor to keep the tile warm even when the air temperature has been satisfied.  And like Brad said, the heat will have a hard time getting through the flooring to the tile, so the floor sensor is essential.



Since there's only one room, I'd be happy to calculate the heatloss.  I need the following information:

- design temperature for your area, i.e. the coldest average temperature

- dimensions of the room (6' x 10')

- height

- square feet of windows and outside doors

- single or double glazed windows

- linear feet of exposed wall

- how many exposed walls

- how much insulation in the walls, ceiling and floor

Brad White

Mike- you can

contact me off-line if you like. For one room, I can calculate that as a courtesy, no problem! Can also create a layout if you like, given you are in my area. 

Alan (California Radiant) Forbes

Heatloss

Maybe let Brad and I calc. the heatloss independently and see what numbers we come up with.  Others could join in as well and we could compare numbers and heatloss software.

Brad White

THAT, Alan, is a fantastic

idea. In a number of ways.

Good suggestion!

Paul Pollets

Electric Mat??

I'd use an electric mat, if the tiles aren't installed yet.

mwalsh3

calculations

thank for the offers to do the calculations - here's the info:



- design temperature for your area, i.e. the coldest average temperature

** I live just north of Boston, and would guess average winter temps are in the 10-20 deg range. We just had one of the coldest days in recent history (-5 for a low) so that's probably a worst case



- dimensions of the room (6' x 10')

** more accurate dimension is 5'10" x 9'3", which includes a 5'10" x 2'8" shower



- height

** 7'7"



- square feet of windows and outside doors

** one window (5.5 sq ft) and 1 interior door (~16 sq ft)



- single or double glazed windows

** double glazed



- linear feet of exposed wall

** one exterior exposed wall 5'10"



- how many exposed walls

** one



- how much insulation in the walls, ceiling and floor

** R15 in all walls, about 12" of blown in stuff in the attic, nothing in the floor



Thanks again.

Brad White

Weather Data and other questions

Being a Boston-based person, I can take the lead on the technical issues, if that is OK.

The ASHRAE winter design temperature for Boston (granted this is at the airport, surrounded by water), is 9 degrees. Outlying areas, but inside Route 128, we would use 6 degrees.



FYI, if you are talking "average", most people are surprised, but Boston winter average is in the  high 30's, 38-39 degrees actually. It is the cold snaps we remember. But the "design" temperature occurs less than half of one percent of the time and this is the number we use, accepting that the record for Boston was -18, recorded during The Great Dog-Hydrant Unity Parade of 1934. Median for January is about 29.5 degrees, half higher, half lower, so you can see the spread. But design, I would say 6 degrees.



Mike, if you can be more specific, we can pin that down further. Not a huge issue in the scheme of things.



Understanding that there is no insulation in the floor, what is the temperature in the basement below? Is it at least indoor basement space?



The R15 in the walls, I will presume 2x4 construction, probably a lot of framing percentage given a window in a short wall, and high density batts. Sound good?



I trust that there is a bathroom exhaust fan. Does this duct directly outside? That can be a disproportionate air leak for a small room, even with a flap damper. But let us know.



Otherwise, enough for me to get started. You other guys?



Brad

mwalsh3

calculations

Brad,



I live in Swampscott, which is just north of the airport - I'm about 3 blocks mile from the ocean. Does that help with the temperature question?



The basement below is indoor space (my workshop) which is ~67 degrees.



The window is new and my contractor beefed up the framing in the installation, so that wall is high in farming percentage and I used the high density batts.



The fan is a Panasonic that vents outside - dampers in the fan itsels as well as outside on the vent

Brad White

Good to go, Mike

That helps. I will still use 6 degrees. How windy is your location? 

Nick W

Heat lamps in the ceiling work well.

We have a weirdly shaped bathroom that is hard to heat. It has 4-1/2 feet of baseboard radiator, but the radiator is poorly located to heat the entire bathroom. The builder wisely installed two 250-watt heat lamps in the ceiling. These add about 20 Btus/sf and make the bathroom very comfortable for bathing. The heat lamps are operated manually with wall switches. They warm up the floor very quickly.

mwalsh3

calculations

wind is not bad at this location

Brad White

First Pass

My first pass has your room heat loss at about 900 BTUH. The variables or rather, where your measurements are not taken precisely, is that you have the net inside dimensions of the space and not the outside edges of the volume. Specifically, your 7'-7" ceiling height does not define the wall height. I would assume 8 feet for those because one has to consider that the "wall between the floors" also has heat loss. Likewise your width and actual conducting area is wider than our net room width. Does that make sense?



Anyway, my first pass is my newer program, LoopCAD 2010, which has a nice little BIM engine to generate 3D views. I took a guess at your joist spacing and orientation. I will follow up later with another method.

Alan (California Radiant) Forbes

Heatloss

My numbers come out way higher than Brad's.  I'm using Slant/Fin's Hydronic Explorer and the heatloss at the design temperature of 6 degrees outside temperature is 1,535 BTU's.



Maybe we need to compare factors:

doors and glass - .65

exposed wall - .07

ceiling - .02

floor - .15

infiltration - .012



Brad calc's. 15 BTU's per square foot and I calc. 26 BTU's per square foot.

Brad White

That was one of my

first times using the LoopCAD program and I will do it both manually and with CHVAC to check it out, but I too was surprised it was that low. It is just one wall and window, good roof. Infiltration is the big dog and that may not be much. I lean towards your numbers though as a gut check.

Brad White

Numbers In

I calculated this by hand and using CHVAC and came up with the same numbers within 5%.  Indoor temp. at 72, outdoor temp. at +6. Delta T = 66F



Rounded, 1,000 BTUH which benchmarks out at 20 per SF. Range 992 to 1018 BTUH.



Factors:

Net Wall: u= 0.071

Glass: u=0.68

Roof: u=0.033

Floor: u=0.05 (but at a 10 degree DT)



Infiltration: Crack method at 0.5 cfm per LF, face exposure method, ACH method (0.75 ACH) and volume method, all came to a range of 288 Btuh to 384 Btuh. I used 375 as an average of the methods, favoring the higher.



Depending on the net radiant area, radiant floors might do the entire load, but I would put in a towel warmer just the same. Loss of radiant floor by the vanity, water closet "hold back" area and such, would favor that.



So, radiant with a floor sensor, small mixing valve and small circulator should be plenty. Roth Mini-Shunt maybe?

mwalsh3

calculations

thanks for your efforts.



Just want to make sure that when we're talking about "radiant" in this case it's the type that can be installed under the subfloor - in my case in the joist bays in my basement as my tile is already installed?



Sorry if I wasn't clear on this from the start

Brad White

Clear to me...

Yes, underfloor with extruded plates, barrier PEX tubing. With radiant, your "back load", the higher BTU loss downward even with insulation, is a decent portion of your hot water heating load because of the higher temperature difference. Even so, your total flow rate will be less than 0.20 gpm. The smallest pump you can find may have you wanting to put radiant floors in the mudroom, doghouse...



Which way to your joists run, parallel or perpendicular to the length of the room? And the spacing, standard 16" OC?

mwalsh3

questions

the joists run parallel to the long dimension of the room. If this does require addition of a new zone to my boiler (?) would it be possible to extend the radiant to the master bedroom? For some reason this is the coldest room in the house.

Brad White

For the effort

and assuming that the underside of the bedroom is similarly exposed below, I would do that too.

Here are the basic rules:



Heat loss needed for each space. If the floor coverings are similar (I doubt you have tile in the bedroom but the overall R value is the same), you can use the same temperature water to each, so one zone to do both.



Regardless of what else you do, yes, you will create another zone, defined by a circulator, mixing valve and controls, to make a reduced temperature water circuit for your floors. If your bedroom has appreciably different characteristics, it MAY require a different water temperature. If we play our cards right, we may be able to get them both to have the same temperature. If the bedroom already has some heating source as it should, then the radiant becomes less critical and we can use it to take the edge off.



But yes, all things are possible and it will justify the base expense of the circulator, manifold and controls. Beyond that it is piping, plates and insulation.

icesailor

Existing Heat:

Waz-up? You have 4.5' of existing baseboard? That works out to be 2200 to 2700 BTU's. More than twice what is needed and calculated. Over the years, I find that a bathroom this size is 900 to 1000 BTU's with 20% added for extra in bathrooms. I always install 3' of Slant/Fin rather than cut it. If it was 1500, I would have gone with 4' rather than risk a cold bathroom if they run the fan in the winter.

If this bathroom doesn't heat properly with 4.5' of baseboard, something is wrong. Those infra-red ceiling lights are piercing the insulation and the heat is being sucked out of the bathroom. For me, personally, there isn't a way on Gods green earth I would put radiant in the floor of a bathroom as small as this without putting a K42 or a "Quiet One" kick space heater to heat this place.

But hey, that may work for you. I've not seen it work for anyone else but it might work for you.

750+ BTU's for the floor? That's a foot of baseboard. If the floor is insulated over a warm space, it should be more like 150+ BTU's.

JMO,

Brad White

The bathroom now

has no heat at all, an oversight.



Good points on the heat lamp disturbing the insulation.

BTW, with radiant, given the insulation below and that it is a "positive", the heat loss is not to the room but to the system. A minor point, I admit.

icesailor

Radiant Floor

Only if the system water is colder than the floor. Heat flows to cold, dampness flows to dryness. If the water in the radiant loop is hotter than the floor, the heat is flowing into the floor.

As I understand it.

Brad White

As far as

room heat loss is concerned, a radiant floor, especially being insulated as it should be, and especially if operating, has no significant heat loss, especially being above a heated or semi-heated space. Point being, when radiant floors are used, the heat loss is a negative number (negative from the total being positive to the space).

However the "load" is factored into the radiant flow and temperature calculation, just is not factored into the room heat loss.

OneHungLow

Roth mini shunt

Hi Brad and all, You mention the Roth Mini Shunt....a nice little ****'y, but limited to 122 degrees. Are there other manufacturers pump packages like this that are comparable with a high temp, 180 degree, zone? The product availability is dizzying for those of us on the low end of the learning curve.

Brad White

122F limit on Roth Mini Shunt?

I did not know that!

If so, what a shame, that nice entry level product.  I learn something new every day.



And for that, today you will be known as "Other One High!"