In floor heating vs extra insulation ROI
Hi everyone, I was wondering if I could get some real world experience feedback regarding installing a warm board in floor heating system vs using that same capital (35-40,000) to invest in more insulation (R50-60 walls / R90/100 ceiling). We will be using quad pane windows and high end doors.
I plan to using a electric based heating system, as I am a electrician and possibly adding solar panels to the property after the first year of living in the house.
I am considering using electric baseboard heaters to heat the home if I choose to go the extra insulation route, or possibly mini splits in a few locations. I live in the Yukon, which has a design temperature of -41 Celsius. Talking with Warm Board, and they don’t suggest using a ATW heat pump for this location due to the cold climate, siting the ROI on a ATW heat pump isn’t there.
I have talked with a local whom has built a LEED certified house here in the Yukon, and with extra insulation and electric baseboard heat has a heating bill of approximately 500$/year! Our heat load calculation on a early design in R48 walls and R 89 attic brought us in at 30,000BTU/Hr or 8.8Kw/h.
Having low energy bills is a important aspect of the build, but home comfort is also important, as we live in a 1974 mobile home currently with R8 attic we are very familiar with home discomfort.
Cheers, Matt.
Attached is a early design of the R49/R89 version.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Appropriate insulation will increase surface temps and mean radiant temps to the point where there isn't a big advantage to radiant. So my vote is for good insulation (air sealing/windows/doors/etc).
IMHO warm floors are more about comfort than energy savings, but with a heat source like a heat pump or condensing boiler infloor heat often means higher efficiencies. There is a risk with infloor of higher energy consumption if proper insulation and thermal breaks aren't incorporated (you end up heating the ground).
There's a bunch of related but separate questions:
* What is the ROI of improved insulation vs more efficient equipment?
* What is the ROI of heat pump vs resistance heat?
* What is the ROI of in-floor heat vs discrete heat units?
* What is the ROI of air-to-water vs air-to-air?
This is a continuation of the discussion we had in this thread: https://www.greenbuildingadvisor.com/question/atwhp-or-electric-boiler
I'm going to answer the first question last because it's the most complicated.
* What is the ROI of heat pump vs resistance heat?
In the previous thread we established that even in your sub-arctic climate a heat pump has a significant COP advantage. How long it takes to pay off depends on the cost of the heat pump and the cost of electricity.
* What is the ROI of in-floor heat vs discrete heat units?
There isn't any. In-floor is about comfort and esthetics.
* What is the ROI of air-to-water vs air-to-air?
Probably negative. The manufacturers of water systems claim they are more efficient, which may be true, but it's marginal. But they are so much more expensive that they never pay for themselves in the lifetime of the equipment.
OK, now for the tough one:
* What is the ROI of improved insulation vs more efficient equipment?
This is tough, because the better your insulation the less of a difference better equipment makes. Think of your friend with the $500 annual heating bill. Let's say he could cut his bill in half with a heat pump. That's great, but it's only $250 per year that he's saving. If the heat pump costs $10,000 to install it would take him 40 years to pay it back. And it's not going to last 40 years.
The flip side is that making your equipment more efficient also reduces the ROI on insulation. Your friend could have gotten a $500 annual heating bill with a heat pump and half as much insulation. Insulation suffers from diminishing returns, as you make it thicker and thicker you get smaller incremental savings. The impact of doors and windows gets bigger and bigger, and you find it gets really expensive to improve their performance.
"What is the ROI of air-to-water vs air-to-air?"
I think this is the wrong question to ask. ATW gives options that ATA doesn't provide such as the ability to mix floor and panel radiators with fan coils, and split the handling of sensible and latent cooling loads across all three. In contexts where that flexibility matters, it's like comparing apples and oranges. Similarly to the question about Warm Board vs. insulation, this is mostly about comfort ROI, not BTUh/cost ROI.
In-floor heating is a luxury product and it’s got negative ROI. If it had an ROI, every single new house would have it.
I’d be shocked if a heat pump didn’t still pencil out well in the Yukon. Unless electricity is super cheap. I’d go air to air before air to water any day.
My hunch is that what's going to pencil out best is:
* Really high levels of insulation
* Minisplits
* Backup resistive heat.
Make the backup resistive heat in floor and then you have both heated floors on the coldest days when you want it most and lower cost minisplits all the time, or the ability to switch it on when it's payday.
Tim, that could be a interesting combo.
That's kind of what I have. I have an air-to-water heat pump, and a three-stage thermostat. Stage one is just bathroom floors, stage two is add radiant heat in rest of zone, stage three is add air handlers. The bathroom floors are on almost the entire winter, a lot of the time they're the only heat on in the entire house.
I really like this. Of course it's complicated as hell, you have to be a mad scientist to get it to work.
I think if you made the bathroom floors the backup heat you'd be tempted to run them all the time which kind of defeats the idea of backup heat.
DC, I agree. This is probably the best overall option.
It would be nice if commenters on this thread indicated whether or not they've ever lived in a building with low-mass, in-floor radiant. Without this type of experience, you are just speculating on how these systems function in real life and what their impact is on comfort.
My home is 100% micro-zoned WarmBoard (.6 ACH PA50, R35 walls, R50 roof, R30 crawl, Boulder CO, climate zone 5). We heat and cool the building completely via the floors, and the comfort level is unlike any other home or building I've stayed in. Bedrooms are cool for sleeping, bathrooms are warm for comfort, humidity is easy to maintain at a healthy 35%, air temps are significantly higher/lower (cooling/heating season) than at similar comfort levels with forced air, and it's completely silent.
All that said, installing these systems is not simple or cheap. For our build, it was the area that demanded the most of my time to get designed, installed, and commissioned properly. The cost of these systems is so much higher than other options that it is difficult to rationalize. But the comfort delta is there. If forced to build a new home again, for me, radiant would be a requirement.
Final thought on insulation. I'm surprised that increasing the insulation level is so expensive. I also expect that there are interesting options with better ROI between your current insulation package and one that doubles the R value just about everywhere. Your building is an easy to insulate rectangle with blown in roof insulation. What happens to your load calc when you add insulation in places it is easiest to add (e.g. the roof). Is the high cost due to having to add more foam on the exterior of the walls when their R-value is increased? Or are there other design details that have to be modified to accommodate the change? Could you substitute some materials to reduce costs (e.g. dense packed cellulose vs. batts in the walls)?
How do you handle humidity during cooling season?
My experience in Colorado is that you don't need much humidity control... I need to keep the saline spray nearby every time I go.
Boulder, CO has perhaps a couple days a year during the cooling season with high outdoor RH. So latent cooling isn't really an issue. Our ERVs do a good job of insulating us from these events when they do happen. I provisioned (power, water lines, condensate drain, control wire) for a fan coil to serve as a dehumidifier in the upstairs hallway just in case, but based on our experience I don't expect to ever install it. Since the hydronic system can already manage different temps for fan coils and floor, adding it would be trivial.
Im not trying to suggest that it would cost an additional 35-40,000$ on insulation costs, I am just suggesting that I would use that money towards insulations, but not all of it.
What are some of the interesting options that I should consider rather than increase the insulation levels?
I think if we were to increase insulation level to R60 walls, we would likely end up doing a double stud wall with blown in cellulose.
How does your hydronic system work? Is DHW on the same heat pump? I’m looking into the sanco2 combi for space and DHW, perhaps with a Harvest Thermal controller. Not cheap.
Adam
Nordic ATW with DHW desuperheater, Tekmar 406/315/553 controls, SanCO2 for final DHW.
In the previous thread we established the climate had 6600 degree days and electricity costs 18.7 cents per kWh. (OP had said 0.187 cents but that can't be right, right?)
If your friend is using $500 per year that's 2674 kWh per year. At 6600 degree days that's 0.405 kWh/degree day. At a design temp of -41 you have 106 degree-days (F) per day and should use 43 kWh per day or 1.79 kWh/hour or 1.79kW continuous. That's just over 6,000 BTU/hr.
If true, that's astonishing. Or maybe it really is 0.187 cents/kWh and it's one hundred times that!
I clearly made a mistake on my original post. Our electricity rate is between 12-13 cents per kw/h
Even at 12 cents he'd be at 10,000 BTU/hr or so.
Usually at this point in the conversation the subject says, "well actually, I supplement with wood" and it turns out he burns five cords a winter...
I just asked him, and it is actually all electric. I haven’t ran his numbers yet but here is a graph he sent me from his blog.
There is a big difference between $500/year vs /per month.
That 1000kWh in Jan of non heating electricity use goes into house heat in the end so that is really part of your heating costs.
Can you share the blog? Looks cool!
Here is a link Paul,
Might have to scroll back a few pages to find his house build. I believe he has built two different projects.
http://forestpearson.blogspot.com
The way I read that graph is that in July he used about 500 kWh and in December about 2000. Eyeballing I'd say it averages about 1250 a month or 15,000 for the year.
One way of looking at it is that July is the zero-heat month, so 500 kWh is the baseline without running heat, so the additional usage from running heat is 750 per month or 9,000 per year.
But Akos is correct that all the electricity that goes into the house helps heat it. So we get the full 15k of heat, or 14.5 if we subtract out July.
That's about five times as much as estimated before, or a much more believable 30,000 BTU/ hour. Which is still excellent and impressive.
Maybe it's a tiny house with no windows and 100/100/200 foundation/wall/roof insulation. Otherwise it's nonsense.
I suppose one would have to put current transformers on the heating circuits to properly monitor how much of the electricity usage is purely heating.
I have yet to see anything that beats the ROI of insulated shutters that
get closed at night in really cold climates. Living as far north as you do -
you have really long periods of dark on a daily basis - you can't see
anything outside anyway so why not close the shutters during the coldest
part of the day?
Here is what you do design wise. Size the window openings to fit standard insulated
door sizes - then order windows sized to fit these openings. Steel or fiberglass
insulated doors are relatively inexpensive ( as long as you don't get carried away with
the aesthetics) and everybody in the building trades is skilled at installing them -
put them on the inside of your double walls and install the windows on the exterior.
This will run the R ratings of the glass up by about 6 at least during the hours of
darkness. You could, of course, construct your own instead of using standard
doors (for about the same price). I have done this several times- it doesn't
cause any problems with building codes - I never had any problem selling the
homes later - never had a single looker make a disparaging remark about the
aesthetics.
I really like your proposed exterior wall sections - pretty good design - you
need it up there! GOOD LUCK!
I have Warmboard installed in zone 6A. 1986 construction retrofitted to 1.25 ACH50 with additional insulation water temps for heating are 80F to 95F. Hot water for the zones comes from indirect DWH..
You only need Warmboard on tile floors, I.e. bath rooms and entry way. Our duct work is limited to cooling and dehumidification not heating. Limit the in-floor heat to specific zones. Can use panel rads or radiant panels in the ceiling for other rooms.
Yeah, if you live some place where your air conditioning has to dehumidify, you have to have an air handler of some kind. Since you have it anyway you may as well use it for heating too. If you live in a heating dominant climate you'll need more heating than what a unit sized for cooling provides, so you can use floor heating to make up the difference.
If you use a multi-stage thermostat you can have the floor heating be the first stage and the air handler be the second stage.