Tuesday, February 9, 2016

Underfloor heat versus handknit socks

One of the first big decisions we made for our whole-house renovation was to use radiant floors, and that was super exciting because I hadn't known you could heat a house so simply.  Wouldn't you still need the odd radiator to take up prime real estate at the windows, or a baseboard heater or a duct forcing warm air into cooler rooms?

Nope, you don't.  If you insulate properly, you can heat your house from the bottom up with tubes full of warm water.  And we are insulating our house properly.  I should have noticed my handknit sock collection trembling a little when we made this connection, but I was busy.

It's possible to cool your house, at least a little, using cool water in the tubes instead of warm, but it's not as elegant a system because hot air rises and cool air drops, and I am pretty sure I read of some difficulty in the process of changing over the temperature.  Chances are that if you put your heat under the floors you are going to have to cool some other way.

But that was just a secondary reason for our decision, shortly before we were ready to apply for our building permit, to go with a forced air system instead of radiant floors.

(Yay! sang the handknit socks, just loud enough to be heard.)

Digression Alert! I'm going to talk about cooling for a bit, so if you only want to get back to the sock part of today's story just scroll down until you see End Digression in bold text.

Our designers' first solution for the cooling element of the house had been to block out heat with low e windows and insulation, and use ceiling fans for emergencies.  But as much as we want to dramatically reduce our carbon footprint, we knew that wasn't practical for us.  In terms of real estate alone - even though we intend never to sell this house - you can't pour that many luxury features into a home and expect to get your investment back without installing a mechanical cooling system. And we're so crippled during the day when it's too hot for us to sleep at night that it didn't make sense to reduce our earning capacity after already reducing our liquidity for a massive renovation.

So next, we were offered ductless mini split air conditioners for the bedroom walls.  If you've never heard of these, all you need to know is that they are perfect for houses that don't already have ducts, and where air conditioning units that go in and out of your windows every summer are unwanted.  Instead, you get a big metal box mounted on the outside of your house where you want the unit to go, which connects through your exterior wall to a big plastic box that's mounted on the inside of your house - in some cases far enough down from the ceiling to allow you to lift the cover so you can change the filter - which leaves you with a unit covering around one by three feet of your wall all year long.

In some applications that looks perfectly fine.  If you have a home with many open spaces so that the unit can cool it all effectively it's better than fine.  But: it has to go on an exterior wall, and by the time we were looking at these units any exterior walls in rooms we might want to cool were full of windows. 

As we discovered much later on our own, wall-based ductless mini splits were never going to work for us anyway because we are not doing an open concept space - we'd need a unit for every single room we wanted to cool, which is not only expensive but a lot of lost wall space in a home that's already quite compact.

End Digression

What killed the radiant floor idea was not the soft hypnotic murmurings of my legion of handknit socks but Ray's simple question, How are you going to keep mice from chewing on the tubes?  As I recall, he actually paused before the word 'chewing' to make a chomping motion with his teeth, for added emphasis.  It was an immediate lightbulb, because mice are a fact of life in our neighbourhood and we have a very happy extended family living in our garage even now.

We've been fortunate and only had a single mouse get inside our home twice in nineteen years, but after battling them every summer at the cottage I know those rodents are both cute and wily.  Also, incredible at squeezing through tight spots.  If we ever had a gap develop for any reason that gave a mouse access to the joist area in our ceilings, that would be it for protecting our heat system.  Our designers said it would never happen but I'd already read through online plumbers' forums where many conversations were posted about this exact problem, and what it meant for water damage and drywall repair while the homeowner tried to salvage their HVAC system and fight mice at the same time.  Even before I read about the woman who opened the door to her daughter's bedroom in the morning on Christmas Eve and found huge chunks of soggy ceiling on the floor, I was done.

Again though - we discovered only recently that the way we were going to install our radiant heat is the least energy efficient approach to a hydronic underfloor system you can possibly choose.Yay for a slow renovation, so we had time to catch this stuff!

Hydronic underfloor heat systems: a primer

There are four ways to install a hydronic (water, as opposed to electric) underfloor heat system in your home, each with their own pros and cons, and for the purposes of this discussion - as in real life as far as I can tell - we will assume that all of them use PEX tubing (a plastic tube that is commonly used in plumbing now because it is so much cheaper than copper pipe, may last for as long as 100 years as far as anybody can guess, and is easy to fix when it punctures, which can happen as easily as the repair.) 

1/ 'Staple-up' - the 'dry installation' approach we were going to use - involves securing exposed PEX tubing to the underside of a subfloor between floor joists.  You will be drilling holes through the joists to allow the PEX to pass through which is probably more a labour issue than a functional one, and you won't lose any ceiling height on either floor.  You won't have to worry about your flooring installation putting your PEX at risk either.  In fact, it's a great solution if you already have flooring installed and don't want to remove it just to add radiant heat, and that's about the only reason to choose it.  That's because you will have to heat both the subfloor and the surface floor before anybody upstairs feels warm, which increases the heat required for the water running through the tubes.

2/ Cement slab - in one of two possible 'wet installations', you can run the PEX through the cement slab near the surface, thereby protecting it from mice and other chewing pests.  This is really only going to happen in a basement, or on the main floor of a house without a basement, where you have to have a concrete slab anyway.  Cement holds its temperature so while you will wait for a few hours for the floor to warm after you turn on the system, you will also be able to enjoy the heat for a few hours after you turn it off.  But cement's mass creates a barrier between you and the heat, so you will have to spend more in energy to get enough heat to justify taking off your handknit socks.

3/ Cement overlaid on wooden subfloor - you can secure the PEX to your plywood subfloor and then pour a thin concrete layer over it.  Sometimes what's used is a gypcrete mixture.  This approach, like option #2, is a wet installation that protects the PEX and allows you to have that slow rise and fall of heat, but requires you to use more energy and a higher water temperature to be comfortable going barefoot.  You'll lose about two inches of ceiling height and you might have to talk to your structural engineer to see whether the floor can support all that extra weight without help.  You'll also want to be very careful with nails if your flooring installation requires them.

4/ PEX sandwich (my own name) - this is another 'dry installation' whereby you secure the PEX to the top of your subfloor, protect the sides of the PEX with plywood built up to the top level of the tube, add reflective material to direct the warm air upward and around, and lay a proper floor over top.  This method puts the least possible barrier between heat and feet to make the most efficient use of your energy costs, but you'll lose about an inch of ceiling height and again: be careful with nails!  This approach is also the one most likely to attract the attention of inventors of products to make the job easier.  Infloorboard, Thermalboard, Warmboard, Roth Panels, and some others I can't remember the names of now are all options here.

In all of these scenarios, you are probably saying Goodbye to regular hardwood floors.  Warmboard does say they're okay because their product is so efficient it allows you to use a water temperature too low to damage hardwood, but certain cowards like me would be choosing engineered hardwood in spite of those reassuring words.  Tile floors are a better choice, apparently, and most people would have that in their bathrooms anyway. You can also use linoleum and of course, laminate flooring, which is probably the best choice of all, especially if you can do it as a floating floor and avoid nails altogether.

Radiant versus Forced Air Heat

We only ever had 1940s radiators in the house up till now, so condo living is reintroducing us to the joy of forced air heating and cooling.  Our impressions: colossal dust, cripplingly dry skin, and frequent nosebleeds.  Clearly we need humidifiers as well, but to think of bringing all of that back into the house, along with ducts that take up precious square footage, when we have all the walls and ceilings open and can put in whatever we can figure out how to afford?  Bleah.

Decision: Radiant

After heaps of research and discussion, we have decided to go back to radiant floors, this time using the PEX sandwich approach for the ground and second floors and a heated cement slab in the basement.  Bob says the radiant floor he had in his last house was pretty much heaven and was like a tapeworm for their energy bills, an image that is mine rather than his and, erm, is actually pretty gross... sorry about that!

At this point, you'd better believe my handknit socks are gathered in a circle, comforting each other.  In the old edition of our house winter saw me wearing socks and slippers every day and sleeping in socks every night.  We had no insulation and when the temperature dropped outside, the gaps between the floor and the wall under the non-functioning radiator behind my desk meant that there was nothing but brick between my toes and fresh snow.  What's to become of them if we have heat radiating up from the floors and it turns out all those people who say their radiant floors let them go barefoot at home aren't just making it up?

Will I still need 62 different pairs of handknit socks????

(of course I will, silly socks.  I'm a knitter!)

Whew! say the socks.


If you've actually read this far you may be wondering what ever happened to the whole cooling component of our HVAC plan and the answer is, ceiling cassettes.

Seriously, we only found out about these a few weeks ago when I contacted a local HVAC supply and service business and met Gord and Brian, who are both just wonderful.  Ceiling cassettes are shallow and white so they create a textural blot of about two square feet, not one inch of which is on your walls.  They tuck into the gaps between your roof trusses, allowing you to have the exterior unit mounted in the least visible corner of your house, and tubing runs through the attic so it just drops down into the room you want cooled.  Which I guess makes it a ducted system, but at least there's nothing in your attic that can leak coolant or drip water onto surfaces not meant to be wet.  We still need one for every room we want to cool because our house is so chopped up into different spaces, and ceiling cassettes are markedly more expensive than wall units, but they're a bargain when you consider that we invested in a brick exterior we don't want covered up, and that every square inch of usable space inside our small house is worth its weight in gold.

We may still need humidification  help, and we'll definitely need a mechanical ventilation system to push all the air around out super-insulated house that is no longer ventilated by gaps in the exterior walls.  If you are interested in how those work, I've done heaps of research on them, too - as I told the very patient Gord, I am a compulsive learner and I love that I'll understand the new edition of our house as well as I did the old one.  But I can't imagine anybody who isn't renovating is going to want to slog through another long HVAC story any time soon!

So: let's just all go now and have a great day and find time to love a handknit, shall we?  And I'll see you tomorrow.  I have something pretty to show you as a reward for today, ha.

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