Is in-floor radiant heat and a stand-alone wood stove a good idea?
Happy New years to everyone!
This year myself and my partner are planning on starting a new home in the spring here on the east coast of Newfoundland. It’s a 2 storey with the main floor on grade; no basement. Myself and her have the plans all sorted and are certainly making progress.
We’ve spent alot of time now looking into all the different heating options that are available, and we’ve stumbled at this point. The only definite that we have so far is that we’re installing a wood stove in the middle of the house on the main floor, possibly this one: http://www.quadrafire.com/Products/Adventure-II-Wood-Stove.aspx.
We were originally leaning toward installing in-floor-radiant heating on the main floor and baseboard radiators upstairs. I would like to use Thermatlantics Air-to-water system which runs off a heatpump: http://thermatlantic.com.
Our last home had In-floor-radiant in the basement and we thought it was great. This was ran off a Aquastar boiler from Benjamin Heat, with their dutch oven which was very pricey to install and very expensive to run.
As we research into heating systems further and further, it seems as though we’re moving further and further away from figuring out what’s best to use. Martin’s article has brought alot of stuff to light as well : https://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-radiant-floors.
We’re in a rural area where firewood is abundant so we’re going to take full advantage of that. The woodstove will be the primary source of heat in the winter. Electricity rates are going to just about double in the next few years (long story) so we’re taking this into account as well. The scenario that runs through my head is that we leave the house in the morning, the wood stove burns it’s fuel, the in-floor radiant kicks in and runs until the slab is warm and by that time we’re not too far from returning home in the afternoon, when the stove will be lit again. I’m worried that constantly heating or partial heating of the slab is going to be very inefficient as the radiant system is going to be running quite a bit in the afternoon, especially in the winter when the evenings are short and the sun is low.
There has been a million questions raised as we keep researching but we’ve decided that the first one we need answered is if it would be good to install a stand alone wood stove if we’re also installing the in-floor radiant heat?
Thanks
Daniel
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Replies
Daniel,
It sounds as if you have decided to depend on a wood stove for most of your space heating. That's fine. It's simple and dependable.
If you invest in a tight, well insulated thermal envelope, your space heating needs will be low. Even if you only feed the wood stove once or twice a day, your house may stay comfy without any backup heat. If you do need backup heat, a simple system will probably be fine. If I were you, I would invest in a very simple backup heater -- for example, a ductless minisplit or a propane-fired space heater -- and invest most of my money in envelope improvements.
I'd compare the DX2W-2 + non-inverter air source heat pump to a packaged Chiltrix system. Probably less expensive and more efficient.
Consider a wood boiler instead of a wood stove.
Daniel,
I'll chime in a bit from experience. I bought a home with in-floor hydronic and a wood-stove. Unfortunately, the builder/previous owner didn't insulate the slab, this left the floor heat nearly useless. I have since insulated the perimeter vertically which helped immensely, but am still opting for mini-splits. There are limited sources for air to water heat pumps available, and my electric resistance boiler would rarely if ever possible be more efficient than a mini split where I live.
As far as the wood stove, I would make sure you get a good quality one. I have a very heavy Vermont castings with a catalytic converter that allows it to burn at cooler temperatures (longer burns) and still not creosote up bad. I would also recommend having a separate, properly sized fresh air make-up that can be isolated. I believe others have recommended PVC or other piping with a valve on it. I rely on outside air for make-up and I'm sure our comfort is suffering near leaky doors and windows.
We also use a fan to help distribute the air around our single story home. You may look into a passive or active air distribution scheme if there will be long hallways and normally shut doors. I can generally heat the majority of the house comfortably with all the doors open, but sometimes need a small space heater at night. We have yet to install our new mini splits. I received them last week.
Given the extended lag between the thermostat calling for heat and the slab getting warm, you may find that you never use the floor heat at all. I'm with Martin: Spend your money on the envelope and a minisplit and forget the radiant floor.
If part of your desire for the radiant floor is the aesthetic feeling of the warm radiant heat, you might look into a masonry heater instead of a wood stove.
When you burn a fire in a masonry heater, it burns really hot and fast, and all the heat is absorbed by a large soapstone thermal mass, which remains warm for a long time, but never gets so hot you can't touch it.
My folks old poorly insulated home had in-floor radiant heat which was very pleasant, but in their new much more well insulated home, they decided to do a masonry heater instead of in-floor radiant.
They have their masonry heater set up with the chimney running through a stone bench, so you can sit on the warm bench and lean against the warm soapstone. The brand they have is Tulikivi, but I'm sure there are at least a handful of options out there.
It's pretty cool! They're not cheap, but neither is a radiant floor.
With the masonry heater, you can ditch the complex in-floor radiant, and use one of the simple backup systems Martin recommended, but still have the magical warm surface to touch and lean against. (Putting your feet on a conventional wood stove is probably not going to be as pleasant)
Hello everyone,I guess the axe has kind of fallen on the in-floor radiant and we'll start looking at other options for a secondary. I was thinking that we may have been looking at this wrong but it's good to have you guys confirm it.
Thanks for your input Martin and Stephen. Thats a good point to sink the money back into the envelope. We've already planned for R-60/70 in the attic, Roxul's comfortboard on the exterior of the house, and XPS under the slab and on the interior of the foundation. I'm sure i'll have no trouble finding other ways to spend the extra $$$.
Thanks as well Jon. I've had the wood boiler before but the system lacked a large buffer tank and it didn't perform as well as expected. If I was definitely going with the radiant flooring then I would go this route again, just a brand different from Benjamin.
Those masonary heaters look great brendan but like you said, very expensive.
It's funny you mention the Catalytic Converter mike. I stopped into a fireplace shop this afternoon on my way home and the salesman was showing them to me. I've seen all kinds of woodstoves, furnaces and inserts before but this is the first time i've seen one with the catalyst in action. They had the stove lit in the showroom so I did get to have a good chat with the salesman about it and see it working.There not very popular around here yet so it's going to be hard to find someone who owns one. How do you find yours? Any downfalls?
"..and XPS under the slab and on the interior of the foundation"
XPS loses R value over time as it's climate-damaging HFC blowing agents leak out, falling to about the same performance as EPS of similar density after a few decades. EPS is blown with relatively benign pentane, and has stable performance over many decades. Rather than XPS under the slab add 20-25% to the thickness and use Type-II (1.5lb nominal density) EPS. On the interior of the foundation walls you can use polyiso (also blown with pentane) or EPS. Both EPS and polyiso tend to be ~25% cheaper per R than XPS too.
Hi Dana, never realized that XPS was blown with damaging agents but I will keep in in mind. I know that the location of the home has damp ground around it, which is also why i'm not putting in a basement, so I was kind of leaning away from using EPS as the water tends to hold up in it and causes it to deteriorate.
I'll certainly keep that info about XPS in the back of my mind though. We'll have to see when we start to dig in the spring and how we do with the drainage.
Thanks
Daniel
Hi Daniel,
We build something similar to you last year in New Brunswick. Very well insulated two story on a concrete slab on grade with a small 10 000btu Canadian made masonry heater (i.e. affordable) that we love, located in the center of our floor plan . We have 3 small electric baseboards as backup for a total electric consumption of $60/month for the house and it's heated garage. The temperature will drop 1 degreeC when unoccupied during the day. We do 1 fire every night. Like you I debated radiant floors but I'm glad not to have gone that route, there is no use for these in a well insulated house. GBA is an excellent source of information that you can trust.
Hello Marc,
Good to hear that this strategy has worked for someone on the east coast as well. I'm going to have a better look at the masonry heaters and see if they fit the budget.
I had radiant heat in the last house and the floor was always warm and great to walk around on. Looking back though, this was probably not a good sign. I can name off a few things that should have been improved on when we were building. Lessons learned though and this next house will have some big improvements. I'm glad I put the question forward on GBA, i'm sure there will be a few more yet.
At 1.5lbs density (aka "Type-II") EPS does not become waterlogged unless fully submerged for years (but then XPS would eventually under those circumstances too), but still retains about 2/3 of it's R-value even at saturation. It does not deteriorate under water, and when the tide goes out, it dries. EPS is even used under roadbeds and airport runways to control frost heaving, which is much worse set of conditions than under a residential slab, and as dock floats, etc.
If the slab is properly set up with 4-6" of clean compacted gravel under it, installing the EPS atop the gravel, with 6 mil poly sheeting above the EPS makes for a warm & dry, clean slab.
Type-II EPS is the most commonly used material for insulating concrete forms as well.
Hi Dana,
Thanks again for the info. I didn't realize that EPS performed so well. I'm working as a carpenter/contractor (still learning the heating and cooling end of things) and it's been a busy year at renovations. I've encountered EPS in a few different locations and it was always in hard shape. In saying this, I don't know what its been exposed over its life and it may not have been installed correctly. This is why I kind of steer away from it if there is a high chance of being exposed to some sort of moisture but I certainly could be mistaken in doing this. I'll look into it a bit more as its alot cheaper here than the XPS. As you say, it just has to be installed correctly. Thanks again for the advice.
Not so fast . Some may appreciate this others will surely not . Annual usage says alot .
All about radiant floors done right .
https://www.facebook.com/RValue/photos/a.340016462575.199306.326447887575/10155571358822576/?type=3&theater
Interesting richard. I have no doubt that radiant floor can be made to work efficiently. In my case though, it's more of a secondary source of heat and the general opinion seems to be that it would be better to sink money into insulation, etc rather than the radiant heat. With power at 11cents a Kw/h and supposed to pass 20cents kw/h in the near future, i think i'm going to play it safe with the wood. There's no mains natural gas available either.
The wood is safe for sure . Heat can also be harvested inexpensively and used for radiant floors . Does not have to be complex , break the bank or be difficult . That stored heat can be mixed down using outdoor reset and be leveraged to heat your house for long periods of time so you can relax and not stoke that fire continuously . Just sayin .
Weighing in late here, but Dan C's question is relevant to us so thought I'd see if you had input. We have radiant heating under wood floor with a wood stove. The hydronic floor is heated by a diesel-fired boiler with a Tekmar control. We notice that the floor works pretty well on its own, but when we get the wood stove going in the evenings and it surpasses the thermostat temp - esp when it's cold at night like now (15-19F) - the floor isn't able to regain indoor heat for nearly a full day. It's clear the floor goes dormant when the wood stove takes over, but is it normal for a hydronic system to take 10-12 hours to catch up again after the fire goes cold? Aside from being annoying, I wonder whether we're also burning through more fuel by trying to augment the heat with the wood-fired stove and then letting the floor play catch up. Any insights you have are welcome. Thanks folks. This thread has been helpful and instructive.
It used to be believed that radiant floors worked best if the flooring material had high heat capacity (sometimes called "thermal mass" but I loathe that term; a general rule of thumb is if someone uses that term they're giving answers unsupported by scientific beliefs. But I digress). People were confusing two different properties of concrete, which is what most early floors were made of. Concrete is highly conductive of heat, which is absolutely what you want for a radiant floor, the more conductive the more even the temperature of the floor and the more comfortable it is.
What the industry has figure out is what you've figured out, you actually want your radiant surface to be as responsive as possible, so that it responds quickly to changes in the thermostat. If you look at radiant heat systems like WarmBoard they have a layer of aluminum for high conductivity, but low heat capacity. WarmBoard advertises "highly responsive" in their advertising.