Design Help/Self Doubt
I'm planning on DIYing a retrofit hydronic system into an addition on my home that is currently heated with an old low efficiency forced air system. Its noisy and leaves the floor cold (slab on grade with hardwood on top).
Plan is to run 3 zones - one for the floor, one for the bedroom/ensuite above and one for the basement (under original bungalow). Bedroom and Basement running radiant panels.
Based on heat loss calc:
- floor needs 16000BTU
- Bed/Bath needs 15000BTU
- Basement needs 6000BTU
I'm in Toronto - design is for -20 outside temp.
NG is expensive here and electricity is relatively cheap.
Questions:
- Planning to use Nordik Electric boiler - the one I'm looking at is 31,000 BTU to keep it under 60Amps. Everything I've read is that heat loss calcs have a large buffer built in. Is this crazy to go under the total BTUs based on heat loss calc?
- Considering adding a fourth zone and leaving it open for future expansion.
- Plan is to add a buffer tank, but waffling on the additional expense. Do I need to add mass of can I just run with modulating electric boiler?
Thanks, and happy to clarify anything if this doesn't make sense.
Bryce
Comments
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"I've read is that heat loss calcs have a large buffer built in."
The heat loss calculations involve a number of subjective decisions by the person doing the calculation. Traditionally, installers have tended to be conservative, which leads to higher calculations, because with combustion equipment the penalties for undersizing are much more severe than for oversizing.
It's really not possible to say whether your particular calculation was done conservatively or liberally or somewhere in between.
I get your total load as 37,000 BTU/hr which is 10.8 kW. I don't know about Canada, but here a circuit can be loaded 80% of breaker capacity, so 60A means 48A continuous which at 240V is 11.5kW.
If your limit really is 31,000 BTU/hr or 9.1kW, is that just for one circuit? Could you add another circuit that has perhaps electric baseboard heaters and 6000 BTU/hr of capacity, or 1700 Watts? At 240 V that could be a 15A circuit.
There's no point in having a buffer tank with resistance heat. In fact, with resistance heat it's simpler and cheaper to skip the hydronics altogether and just embed heating wires in the floor.
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Are you absolutely sure electric will be cheaper than gas? It rarely is.
Use this with actual delivered fuel costs.
https://coalpail.com/fuel-comparison-calculator-home-heating
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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This article shows how to estimate your heat loss from past utility bills:
37K BTU/hr for Toronto sounds low, I don't think it's being padded.
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Thank you both for the quickc responses!
I've attached some images: two are the architectural drawings to provide context for the space and two are my rough drawn schematics for the system. Any advice or cautions?
@ Hot_Rod - Yes, I'm reasonably confident that carbon based fuels are only going to get more and more expensive. Not to suggest electricity will not increase in price as well, but the sin taxes of burning gas are only going to increase, particularly in Canada. Additionally, since temp lows (greatest load on the system) are typically overnight, electricity rates are extremely low during peak demand for the system as I understand it…
@DC - Thanks for the note re: buffer tank, thats what I figured but wanted to be sure. The reason to keep it under 60Amps is that I have an existing breaker from an old hot tub that I plan to repurpose with little to no need for Electricians.
You make an excellent point re: embedding wires, I have definitely considered that. Two things I like about the hydronics is that the fuel source is modular (it can be changed if energy rates shift dramatically) and the general comfort level provided by non-drying constant radiant heat. Its definitely on my mind though for cost/complexity reasons.
The 37K BTU seems low but recall that the footprint of the addition is only 400sqft. The rest of the house is heated by a forced air furnace. I also have a gas fireplace in the lower level of the addition thats good for 18,000 BTU if needed.
Do either of you, or anyone else for that matter, have any experience with the Nordik brand? Or performance/longevity of these electric boilers in general?
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"Two things I like about the hydronics is that the fuel source is modular (it can be changed if energy rates shift dramatically) and the general comfort level provided by non-drying constant radiant heat."
Agree about the modular part.
To the second part, the "general comfort level" of embedded wires is exactly the same as embedded tubing.
And it's not really true to say that hydronics is "non-drying." Drying in winter comes from outside air infiltration, the outside air is very dry. It's that forced air is more drying, because it creates zones of higher and lower pressure within the house which tend to increase infiltration. This is less of a concern in modern houses which are tighter anyway.
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Most of the electric boilers modulate their output, no need for the buffer.
What is the total square footage that you are heating?
I know in them Quebec area there are a lot of dual fuel systems, oil and electric. Electric kicks in when off peak hits. Someone up there makes a control that knows when real time of off peak rates hit to turn on the electric.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Here is the link to the Nordik website: they appear to be a rebranding of the radiant heat part of another company called Ecosolaris. Quebec based.
Boiler is modulating and comes with lots of controls and outdoor reset. (Mini-Ultra 9kw)
Family room radiant is 400 sqft (slab on grade)
Bedroom/Bathroom is 400 sqft (second story)
Basement is 442 sqft (largely below grade, insulated exterior walls, good/newer windows)
Total = 1242
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- floor needs 16,000BTU
- Bed/Bath needs 15,000BTU
- Basement needs 6,000BTU
Family room radiant is 400 sqft (slab on grade)
Bedroom/Bathroom is 400 sqft (second story)
Basement is 442 sqft
OK, I didn't realize the areas were so small, that's actually a pretty high load. What kind of radiant panels are you considering for the upstairs rooms? Just for comparison's sake, you'd need 32 feet of baseboard radiator to get 16,000 BTU/hr, which would take up most of two walls on a 400 square foot room. So getting the panels to physically fit is something to think about.
Basement is 15 BTU/hr per square foot, that should be surface temperature 7.5F above room temperature.
One thing to consider is water temperature, you don't want the basement floor too hot or it will be uncomfortable and hard to control. Best is to have it modulate automatically with an outdoor reset. At the same time, the output I gave above for baseboards is for 180F water, output drops as water temperature drops. So you may not be able to run both upstairs and basement at the same water temperature, which complicates things a little.
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I'm planning radiant panels for both the bedroom and the basement as the basement ceiling height is already fairly low and I don't want to lose height so will run the same temp for those two zones. The radiant floor in the living room area will run at a lower temp with a mixing valve at the boiler panel.
I think my heat loss calc is way off. I just used a different calculator (Stelrad room calculator as those are the radiant panels I'd like to use) and got the following BTU requirements. The below figures should make more sense and make it easier to fit appropriate rad panel sizes.
Bedroom/Bathroom - 8700 BTU
Living Room - 13000 BTU
Basement - 6942 BTU
Does that make more sense?
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I'd be wary of any "calculator" that doesn't ask you what's above the room, below the room, how many feet of exposed walls you have, how much insulation is in those walls, how many windows you have and how big they are and what type.
Rules of thumb just don't work. Every house is different, every house is hand built. If you're going to estimate heat loss you need to know a lot of detail about how the house is built.
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Thank you, all fair points. Fortunately the Stelrad one does all those things.
The new numbers make more sense to me, and definitely make more sense when considering the amount of rad panels I'd need with the original numbers - there is no way the room should require that much heat with low e windows and reasonably good insulation.
A good support for this is that with the current forced air system, all upstairs vents are closed in the winter months to direct the heat into the living room area below. If those vents are open, it is too warm up there and the living area is cold. This is one of the reasons I'm increasingly frustrated with the forced air - it just doesn't do the job well.
Thanks for your help with thinking this through, anything else with the design/thinking you'd be wary of?
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A manual 3 way mix valve works well, for the mix down temperatures, it modulates with the ODR.
140- 160f is a common panel radiator design, you may not ever ned 180F if you size them based on SWT.
This issue has some good thoughts about low SWT systems
\
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream2 -
I also have a gas fireplace in the lower level of the addition thats good for 18,000 BTU
Have you lived there long enough to know if the 18,000 BTU is sufficient on a +23 degree F day? Half-way to -20F? Then 36Kbtu would do.
My 18Kbtu fireplace will warm one 360sf room, barely, at +10F with rest of house curtained-off and low ground-loss. Slab-on-grade will really suck heat, unless you can afford to keep it warm most of the time (heat stored in soil many feet down).
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Yes. Its a relatively new Valor model, very efficient at heating the room even in -20 C. (sorry, not good with the F numbers.)
Radiant will be laid in a new insulated slab on top of the existing slab. 2 inch insulation, 2 inch pour. Shouldn't get much heat loss downwards.
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"The new numbers make more sense to me, and definitely make more sense when considering the amount of rad panels I'd need with the original numbers - there is no way the room should require that much heat with low e windows and reasonably good insulation.
A good support for this is that with the current forced air system, all upstairs vents are closed in the winter months to direct the heat into the living room area below. If those vents are open, it is too warm up there and the living area is cold. This is one of the reasons I'm increasingly frustrated with the forced air - it just doesn't do the job well."
The issue isn't with forced-air technology, it's that the system you have isn't well designed or implemented.
Now I'm going to be blunt: reading your first paragraph there, you're headed to the same destination with your hydronic installation. Getting a proper heating load is the single most important step in the design of a heating system. Get that wrong and you'll never be comfortable. These things aren't magically self-correcting. It's not a matter of what looks right or makes sense. There is a process for calculating heating loads, it's called a Manual J. With new construction it's pretty straightforward, there's no guessing about what's in the walls or what the windows are. There is some subjectivity in the Manual J process, mostly about assumptions, if you want to quibble with the outcome those assumptions are the place to look.
In existing construction, where you have a heating history, you can sanity check the Manual J by comparing actual fuel usage and weather against what the Manual J predicts. I posted a link above with instructions for that.
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Bluntness forgiven, however its a bit presumptuous/condescending to suggest I'm "headed in the same direction" considering I'm doing this homework and other homework you have no awareness of. I guess thats the contrarian thing…
I have been working on a Manual J calc over the last couple days (these things take time, I'm not an engineer and even they seem to avoid it) and have confirmed the above numbers from the stelrad calculator +/- 5%. I think thats pretty damn close. I'm also getting multiple quotes from HVAC contractors as this is definitely a DIY job that will stress me out.
Thanks for your help
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Why do you want to limit the boiler to a 60a feeder? Is that the limit of what extra is available in your service or do you only want to run one feeder to it?
Edit: I skimmed for this but didn't find it until i read more closely. Did you do the load calculations on the service for this load? Someone needs to do that. Just because there is a 60a breaker doesn't mean that there is that much capacity in the service. Make sure the boiler you pick modulates and can modulate down to the load of the smallest zone. Many electric boilers modulate but some models do not.
If there is more capacity in the service I wold consider using something like oil filled electric panel radiators for the basement zone or some other direct electric emitter to keep the load within the available output of the boiler.
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Great question re: load on the service. I will definitely run that before I make any final decisions. The boiler I'm considering is from Nordik Radiant. It is modulating, and has an ODR. Based on my more accurate load calculations, the 9kw boiler draws 37.5 amps and generates 30,000 BTUs which is about 5% more than max load on my proposed system. I'd like to keep it all on the hydronics if possible, but good idea, thanks for the suggestions.
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I sort of wrote that as i was reading thought the 15 or so comments. It looks like the proposed boiler is adequate but i wrote some of that before I dug through all of the comments about the heat loss probably having been overestimated initially.
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I know you said you want to keep it all hydronics, but instead of the radiant panels upstairs you could do electric baseboard heat. It would give the same comfort, cost the same to operate, and be quite a bit cheaper to install.
You have to be careful not to overvalue the future upgrade path. While nothing is harder to predict than the future, in this case I'd say it's probably going to be an air-to-water heat pump. If that's the case, it's probably going to run at a much cooler temperature than an electric boiler. Which is probably fine for the basement floor, but means the radiant panels would have to be upgraded anyway.
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Stick with hydronics if you can.
Did you run any fuel cost comparisons?
This is from 2022 in the B.C. area, probably google similar data for your area.
A high efficiency boiler could be as efficient as the high or mid efficiency furnace, properly designed for low temperature operation.
Yes the load is a good first step, most mod con boilers have a wide output range.
A 50- 80,000 BTU mod con would almost certainly cover that load.
/
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Toronto Hydro rates:
On-Peak 18.2 ¢/kWh
Mid-Peak 12.2 ¢/kWh
Off-Peak 8.7 ¢/kWhGas is sold in Canada by the cubic meter. One cubic meter is 36,000 BTU gross. Let's assume 85% efficiency, so 30,600 BTU net. That's equivalent to 9.2 kWh.
Natural gas rates in Toronto range between 6.4 and 15.6 cents per cubic meter. I can't figure out why it's such a big swing.
Even at the highest rate, 15.6 cents per cubic meter, it's equivalent to 1.7 cents per kWh. That's less than one fifth of the cheapest off-peak electric rate.
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I hear you DC, but keep in mind that the sticker price of energy (in Ontario at least) is far from the delivererd price after surcharges and taxes. I ran the calculation on my bills from Jan 2023 last year and the average delivered cost of electricity was $0.20/kwh and gas was $0.095/kwh, so just under half the delivered cost.
Still a big difference - and definitely swinging me to NG. It just bugs me that I'm going to end up with an NG boiler with 2x or more capacity than I need (granted modulating). It just seems so wasteful/excessive. I'd also rather not burn gas. No need to get political, but every bit counts (and Ontario's grid is close to 75% non-carbon energy and rising). Pocketbook still outweighs most things though, so points well taken.
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Emitters are forever. Mod-Cons and AtWHPs are consumable parts. Skate to where the puck will be. Design your emitters for low temps from an AtWHP. Use an NG modcon for the next 8 years. In 2032 the Mod-Con will be unrepairable e-waste junk, and you can replace it with an AtWHP.
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Why not AtWHP now? If I am designing the system for it, and have not purchased a boiler yet, is there a reason to wait 8 years? Is the expectation that heat pumps will get better/more efficient? Or cheaper?
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Well there is a ton of misinformation on here unfortunately about modcons and A2WHP unfortunately. I still can get parts from Viessmann for the very first modcons they ever sold in the US. We can still get original munchkin parts, The first run of Baxi combi boilers that ran through Michigan for a short time still have parts available. modcons are not some "unrepairable" or "consumable part", the only people would say this have trouble working on them or can't understand them. I don't have as much experience with A2WHP, but there is something to be said here about the tech being much less understood by installers, they have been around for some time now though, and there are several good brands that will offer good warranty. Locally in climate zone 6 we have several very qualified installers for A2W, we aren't fully replacing heating systems with them here yet, but if you are in a more mild climate zone you can definitely make it happen
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better, more efficient, cheaper?
Great question.
I love sharing my opinion here because it pisses people off. People who don't like hearing from me because I'm not in the trades or industry. But I'm good at cutting through marketing BS.
I expect in 8 years for AtWHPs to become :
more common
more of a mature product
more of a commodity product
more experience in sizing and installing them
Probably not more efficient than AtWHPs of today. Maybe a little better in terms of product life. Also known as MTBF, (mean time between failure). Still won't be a great MTBF. Like my inefficient 75 year old boiler.
Comparing Fuel costs, today NG is usually cheaper. In 2032, who knows. So you get most of that 8 years of cheaper fuel costs.
TCO. Total Cost of Ownership. Your generation is being ripped off on TCO. You are being fed a stream of increasingly short lived and unreliable products. It's the elephant in the room that no one wants to talk about. Politicians, environmentalists, and bureaucrats all either don't get it, or hope that you don't get it.
But today the bureaucrats are going to get smacked back into their place, at least in my country.
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@WMno57, you said, "I love sharing my opinion here because it pisses people off." How about sharing your opinion so that you can help people instead of reveling in the fights you're picking? There's so much nastiness on the Internet already and it is not welcome here at Heating Help. This site is a place where we can come together and help one another. If you're looking to stir things up, take it somewhere else. And this is my final warning to you about bringing politics into a discussion.
President
HeatingHelp.com2 -
@Brillico I apologize for derailing your discussion.
If you want to reduce your carbon footprint, do it. Look into AtWHPs. They will use less electricity than an electric boiler. Most important step now is to size your emitters for the output temperature of an AtWHP. They will still work with an electric boiler or modcon. Modcons get their highest efficiency numbers on oversized emitters because they can condense. An electric boiler would cycle more on oversize emitters, but that might not be noticeable. Electric boilers are always 100 percent efficient, no mater the duty cycle.
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There is a lot of innovation happening in heat pumps right now. The innovations tend to make it to market first in the most popular products, which is air-to-air. Air-to-water is a niche product, so innovations take a while to get there. So if you want to see where Air-to-water will be in ten years, look at air-to-air today.
Here's a chart I made comparing two air-to-water heat pumps, Arctic and Chiltrix, against the Mitsubishi M-Series, an air-to-air heat pump that I consider to be among the most technologically advanced. The X-axis, across the bottom, is outdoor temperature in C. There are two different groups of lines. The top three show COP vs. temperature, the green line is Chiltrix, the orange line is Mitsubishi, the blue line is Arctic.
The second group is output vs. temperature, which is scaled as a percent of nameplate capacity since all three have different capacities. Top line is Mitsubishi, then Arctic, then Chiltrix.
The Chiltrix is a single-stage heat pump, the Arctic is a two-stage that produces hotter water, and the Mitsubishi uses a technology called vapor injection.
The big benefit of vapor injection is the way it keeps its capacity at cold temperatures, if you look at the -20C line the Chiltrix has less than half of its rated capacity, the Arctic has about two thirds, and the Mitsubishi is up around 85%. So for your 37K BTU heating load at -20 you'd have to install about 80K of nameplate capacity with a Chiltrix but about half that with a Mitsubishi. Or alternately you could install the same capacity with the Chiltrix and supplement it with resistance heat — which would wipe out the COP advantage of the Chiltrix.
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NYSERDA has been doing a lot of testing and evaluating of A2WHP maybe look around their site
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0
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