Bathroom remodel: underfloor heating and related decisions

Discussion in 'Remodel Forum & Blog' started by MidAtlantic, May 13, 2014.

  1. MidAtlantic

    MidAtlantic New Member

    Messages:
    4
    Location:
    Southern Ontario
    Hope this is the right section of the forum for this fairly wide-ranging question. Also hope that this long essay doesn't put everyone off reading my post :p

    Edit: please note that based on what people here are saying and some other discussions I've had offline, I've already changed my mind quite a lot since I wrote this post. My planning got so complicated because of the separate zone for the underfloor water heating, so I'm now thinking maybe a small electric underfloor heat may be the best way forward; if it's small and used sparingly, it need not be too expensive.

    TL;DR: I'm a beginner reno/DIYer. We want underfloor heating, started looking at water underfloor heating, then started realising this might mean lots more decisions. Need help figuring out my plan please.

    I've lived in rented places for a long time, followed by a fairly modern condo with my wife, but now we have our first house. The house is solid, but it's old by North American standards; our best guess is that it was built in 1906. It has water radiator heating and no ductwork, and we'd like to keep it that way. We're in Canada, so although sometimes it can get a bit hot in summer we have a window unit for the bedroom those few days when it's too hot to sleep.

    I'm currently interviewing contractors to remodel the main bathroom in our house, which is mostly from the seventies, apart from some newer tiles & taps (maybe from the nineties?) With our first kid due to arrive in November, we're thinking that the time to gut & remodel the main bathroom is now, and not next year when we will have a baby and will be getting no sleep etc.

    Most of the decisions are fairly easy: tiles, vanity, sink, bathtub, shower head, taps and so on. Where it gets more complicated is that we would like to add underfloor heating.

    I know there's two main types: electric and water. We plan to live in the house for a long time, so I'm more or less dismissing electric due to the significantly higher operation cost & lower efficiency. I know electric is generally much easier to install, however. I'm not completely closed to the idea of electric, but it would take a lot to convince me that this is a good idea.

    So: water underfloor heating. I understand that the best way to do this is lay PEX and then overpour: great thermal mass. Unfortunately this idea is probably out as I don't think the huge extra weight would do our old semi-detached house any favours. Without overpour, some other solution is needed to get the heat to where it needs to go.

    We also need a separate circuit for the underfloor heating, since I believe it's not good to run radiator-temperature water through underfloor heating, despite what a couple of general contractors have told us recently.

    At this point the simple (hah!) bathroom reno project planning arted looking more complicated. I took a look at our hot water equipment in the basement, and figured out that it's fairly old. By looking at the serial numbers and some websites, I now know that we have a Kenmore Economizer 6 tank (August 2001), and a Slant Fin Galaxy 125 boiler (around 2005, but Slant Fin serial number system is weird so hard to tell exactly).

    Clearly, the tank is near the end of its useful life and the boiler is getting old too. Although we haven't had any issues with either of them yet, I'd rather replace them with a Grade A modern efficient solution... and before they decide to go kaput in the middle of a Canadian winter.

    If it isn't obvious already, there's a lot I don't know about plumbing. I'm fairly handy and definitely technically-minded, so I'm not afraid to read through complex stuff if it will help me, but I am trying hard to educate myself before I start spending too much money. Figuring out exactly what my plan should be is the first step.

    So the decisions I'm facing include:
    • Electric or water underfloor heating? Probably water, but would like to hear any and all ideas.
    • Best way to ensure that underfloor heating is efficient? Without overpour, I think the best option may be aluminum plates to direct heat upwards through the tile and towards our toes. I know I don't want to waste lots of money heating the joist space.
      [*]Separate water circuit needed for water underfloor heating? I think so, but what's needed to make that happen?
      [*]Replace water tank and/or boiler? Probably a bigger question, but if there's any advantage to getting the work done at the same time, I need to consider this now. Should I try to get this work done in one hit? Should this question be in one of the specialised forums for boilers/heaters?
      [*]Other stuff that maybe I'm not thinking of...?

    I'm pretty sure that there's more info I'll need to post if anyone is going to have a chance of helping me, and I'm happy to do that. Appreciate all advice and thoughts from anyone who has taken the time to read this far. The #1 thing I've learned so far is that there's a lot I don't know, and #2 thing is that doing your research beforehand will [hopefully] save upset and wasted $ down the road.

    One last thing: I may not bring much plumbing/reno knowledge to the forum, but I can almost certainly help with computer stuff. I'll try to keep an eye on that forum too.

    Edit: please note that as I'm a new user here my replies aren't showing up, although I am responding! It says a Moderator needs to approve them before they will appear. Sorry to those who have taken the time to respond to me - I am grateful!
    Last edited: May 14, 2014
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,137
    Location:
    New England
    Well, you're correct in that you need to limit the water temperature you use in radiant in-floor heating. You need to restrict the floor surface temperature to a safe value, and you can't use something like 180-degree water to get there! Well, you can, but you need to temper it first to only feed that section with cooler water. So, all you may need is a tempering valve, but it's usually more complex than that.

    Electric in-floor is usually called floor warming. Depending on where you live, you MIGHT be able to use that as all the heat you need in the room, but you may not. While you an get lots more heat out of hydronic, the max limit on electrical is in the order of 10-12W/sqft. That translates to around 35-42 BTU/sqft. In some places, that's more than enough, in others, it might take the chill off the floor, but not much else. There's a limit on how close you can put the wires with an electric warming system, but with the larger size and pumped fluid and no (well, not as much) conflict with radiant, you can make it much more dense, should you need it.

    Note, there is more than one light-weight hydronic screed system out there. YOu might want to check this out as one example...http://www.schluter.com/9_1_schluter_bekotec.aspx . With that type of product, you combine several functions into one: easy layout and installation of the tubing, an uncoupling mat, minimal height buildup, much less weight verses full depth embedding of the tubing, quicker response time since there isn't as much thermal mass (but it is still nice and even), and more.

    You could keep the radiator, or whatever in the bathroom, and then just warm the tile when you want with electric, which may not be a bad solution. WIth the room already warm, it doesn't take as much to just take the chill off of the tiled surfaces. And, you could use that on a cold morning when you don't need the heat. If you have pets, they'll love it, and so will your feet.

    Before you go anywhere near replacing the boiler, you need to get a good heat load analysis done, or attempt it yourself. The trend is still (unfortunately) to way oversize a boiler. This is lousy for efficiency and long life, not counting that it costs more to buy. Most older boilers are at least 2x oversized, and some a lot more. Depending on what you are using for heating the rooms, you can often use an outdoor reset controller, that will adjust the boiler's output to just make it warm enough, so most of the time, it will be running longer, but at a lower output (this would be with a mod-con, modulating/condensing boiler). With one of those, cold-start boilers, there's no penalty for making your hot water with an indirect water heater...it uses the boiler, usually on a separate zone, to heat the water for you. Faster reheat, so you can usually use a smaller tank, and because there's no flue, the standby losses are quite low and they're very efficient.

    One thing to look into is whether there are any government or utility rebates available to help offset some of the costs of doing this sort of energy efficiency upgrades. If available, they may have restrictions on what you can put in, and it can vary, based on the efficiency improvement you're getting. That can sway your decision one way or the other.
  3. MidAtlantic

    MidAtlantic New Member

    Messages:
    4
    Location:
    Southern Ontario
    Thanks Jim! This is definitely food for thought.

    In fact, since reading this and having a discussion with one or two people, I think there are two important things to change here:
    #1 is we're going to forget about underfloor water heating. I know I said I was fairly set on it, but when I take stock, it's the water underfloor heating which is the cause of my confusion & stress here. No need for fancy additional plumbing, no need to design additional water circuits or use arcane valve solutions. It's a small bathroom, and a correspondingly small electric underfloor loop on a timer need not cost too much to run now and again (or even just in winter).

    There's actually no heating at all in the bathroom right now, so I'm thinking maybe a towel radiator would be a great addition.

    This is something I've recently come to learn from reading. The second takeaway is related to the first: #2 is that I shouldn't include changing my water heating equipment as part of the bathroom reno, and if I don't install water underfloor, I don't need to. I can replace them at my leisure.

    I will be on the lookout for rebates when I do come to do that work, for sure.

    Thanks again for taking the time to read my post and respond in detail; it's helped me organise my thinking and I can see a clear path to success now.
  4. Dana

    Dana In the trades

    Messages:
    2,919
    Location:
    01609
    In a bathroom you have limited square footage to deal with given the plumbing fixtures & cabinets, and you DON'T want to heat the floor under/near the toilet.

    If the rest of your heating system is high-temp (150F+ water) a suspended-tube radiant floor is pretty cheap to install, and gives you the cushy warm-floor thing, but you may need to augment it with a heated towel rack or a short piece of baseboard or something to meet the design heat load. Only if you're planning to go with a low-temp radiation in the whole house to max out the efficiency of a condensing boiler would it make sense to micro-zone the radiant floor with a low-temp sort of approach.

    With hi-temp suspended tube you'll want the tubing to be about 2" below the subfloor, 2- runs per joist bay, and 2" off the insulation below, keeping the tubing at least a foot away from the toilet, and insulating the subfloor & drain pipe near the toilet.

    How big/what type is the current radiator in the bathroom? Does it keep the bathroom warm enough, or would you like it a bit warmer in there? How many square feet of radiant floor can you get?
  5. MidAtlantic

    MidAtlantic New Member

    Messages:
    4
    Location:
    Southern Ontario
    Duly noted about the toilet - thank you. I assume that's because it could do bad things to the wax ring seal and no-one wants a leaky toilet...?

    As I've said, I'm no expert, but isn't that quite inefficient? My understanding is that you end up paying to heat the joist space. If I'm wrong, well... I'm here to get myself an education so I'd welcome the lesson!

    Any changes I make to the heating of the house will be piecemeal. We can't afford to redo the entire house all at once, and we also have to live in it, so the high-temp radiators are here to stay. If I was building a new house from scratch, I'd put in heavy concrete floors everywhere and in-floor water heating, but this is an old house and I need to work with reality and our budget :)

    The heated towel rack is likely where it's at for us. I like this one: http://www.doorsixteen.com/2011/03/21/my-friend-the-towel-radiator/.

    Currently there is no heating in the bathroom at all(!) which means that in the Canadian winter it's pretty chilly in there and we often end up running the shower for a couple of minutes prior to actually getting in. Obviously that's not a very efficient way to heat a room...

    When I eventually redo the kitchen, I will look at a microzone for in-floor water heating and a heavy high-thermal mass floor for that, since I'm also planning to redo the basement and it would be relatively easy to provide the necessary support via the foundation, whereas the bathroom is on the second floor so I don't dare put the heavy floor needed for high thermal mass in.

    Not many; the room will be around 7x9 feet (once I'm done moving the wall to expand it) and you have to factor in a bath & toilet as well as a slightly irregular shape. Maybe 30 at a rough guess?
    Last edited: May 14, 2014
  6. MidAtlantic

    MidAtlantic New Member

    Messages:
    4
    Location:
    Southern Ontario
    I've actually changed my mind: I think a small bit of electric underfloor heating is the best choice for my sanity, as it's the water heating which is making my plans so complicated.
    I'm planning to add a heated towel rail, so the underfloor only needs to be auxilliary/nice for the toes.

    Thanks - saved for future reference.

    Yep. This is actually what I'm going to do, despite my original post being very pro-water-heating.

    I'm going to keep it simple by avoiding the headache of water-based floor heating and separating the projects: worry about the bathroom, then replace the old hot water heater tank with a new efficient one. I'll certainly look out for rebates, although I bet my wife finds them first as she has a knack for that sort of thing :p

    When it's time to replace the boiler, I will certainly make sure I do it properly. Until a few days ago, I would have assumed bigger == better always, but I'm now seeing that it ain't necessarily so.

    Thank you for taking the time to respond in detail. I did reply yesterday but I think the forum ate my post.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,137
    Location:
    New England
    The only time bigger could be considered better is if you regularly do deep setbacks, either because you're not home that much, or whatever...the house will come up to temp quicker. But, it takes awhile for the whole house, the contents, etc., to cool way down if you have decent insulation, so for shorter setbacks, you can...the better the insulation and the closer to design output, you may find it is more efficient to just let it run, since it will normally be running at a more economical (condensing) level...running full out, things will be too hot to condense much, if at all.

    Ideally, on the coldest design day, the heating system would run constantly and just be able to provide the amount of heat that is being lost. Constantly running ends up being much more comfortable. And, a good part of the inefficiencies of any heating system are when it first turns on and then off again. The smart ones can modulate to adjust their output to what the house needs and run longer at that low level. But, most houses, with any kind of insulation and decent windows, actually probably needs less heat on average than the smallest modulating mod/con boiler can provide, so you lose some, even with them.

    It is critical to get the thing sized properly for max efficiency and comfort. ANd, by using a smaller one, closer to the design needs, your out of pocket to buy the thing is smaller, too.
  8. Dana

    Dana In the trades

    Messages:
    2,919
    Location:
    01609
    Any heat that goes into the joist space is still inside the thermal envelope of the house. The temperature inside that joist bay might hit 35-40C, which increases the heat loss at the 3-4" of band-joist on the end, but you can (and should) insulate that band joist to at least R20, if it' isn't already, and there should be at least R13 below the tubing to keep it from heating the room below (much). It's the heat-loss equivalent of adding 2" of room height to the walls- not exactly a deal-breaker, and not very different from the edge losses of a heated 4" slab.

    To isolate it from room below R15 Roxul or R13 fiberglass 2" below the tubing with cheap aluminum foil (the stuff used for your kitchen is good enough- no need for overpriced aluiminized polyester bubble-pack "radiant barrier" ) laid on top to reflect the radiated heat off the tubing and subfloor back at the subfloor works. The effectiveness of the aluminum will fade a bit over a few decades as it collects dust, but it's not a critical factor (you could even skip it if you wanted to.)

    It's not so much that suspended tube is inefficient, but that it is not very responsive to rapid changes in heat load, and has somewhat limited total heat delivery per square foot. If you've been doing OK with no heat emitters in the room at all, 25-30 square feet of full water-temp suspended tube will likely be enough even without the heated towel rack.

    Systems such as Ultra Fin can deliver over 20BTU/hr per square foot, which may be more than the room's total heat load, and might make the floor uncomfortably warm to bare feet with 150F+ water pumping through it.

    Don't oversize the heat output of the towel rack either- the Runtal in the picture on that link can probably more than heat the space all by itself.

    For purposes of roughing out the heat load of that bathroom, how many square feet of exterior wall does it have (and what is the wall construction type/insultion), and how many square feet of window (type & U-factor, if you have it), and assuming you have an insulated attic above, how much insulation? A postal code or nearby city would be useful for looking up weather data to figure out roughly where the 99% outside temperature bin lies to come up with a design temperature. Most place in southern Ontario have a 99% outside design temp between -20C and -15C, but there are both warmer & cooler places. From there we can do way better than a WAG on how much of the load would be covered by suspended tube floor, and how much towel warmer would be too much.

    When micro-zoning it's important to have enough radiation &/or thermal mass on each zone that you don't end up short-cycling the boiler into low efficiency and early mortality. The Galaxy 125 probably has about 125,000 BTU/hr input and at least 100,000 BTU/hr of output (and is probably at least 2x oversized for your actual heat load). There isn't sufficient thermal mass in the boiler itself to keep from short-cycling, so it's up to the system designer to prevent that by guaranteeing a minimum radiation on each zone.
Similar Threads: Bathroom remodel
Forum Title Date
Remodel Forum & Blog Bathroom Shower Remodel Jul 5, 2014
Remodel Forum & Blog Big problems arise after bathroom remodel: advice needed May 8, 2014
Remodel Forum & Blog Bathroom remodel with wall hung toilet. Need advice on plumbing and venting. Mar 10, 2014
Remodel Forum & Blog Bathroom remodel: Project management software Jan 14, 2014
Remodel Forum & Blog Bathroom remodel - This looks like a big mistake, what do I do? Sep 19, 2013

Share This Page