Electric vs. NG Boiler

[iron]

In our new house build, we are planning to use radiant floor heating. We are considering installing solar panels as well as our area is favorable for power generation. I assume a NG boiler is far more "efficient" to use to generate the energy for the heating system, but I am wondering if going to electric to make the most use of our solar panels would be better. I don't have the energy audit yet for the house (soon), but wanted to get some opinions on the matter. In BC, there are very limited solar incentives like in the US, so our breakeven will likely be many many years out if going with solar. We do have an EV, but I suspect we'll be driving less than 8000 miles a year here in our small mountain town (plus there is free charging in town)

 

[ABMax24]

Purely in terms of cost effectiveness of install and operation you will have a very hard time beating a condensing natural gas boiler, plus it you get a combi-boiler it will also serve your hot water needs.

Now if you want to consider CO2 emissions then electric has its advantages (at least in BC), but for in-floor heating I would suggest looking at a heatpump setup instead of purely resistive heating elements. In floor heating utilizes relatively low temperature water which is where the performance of a heat pump shines. If you so choose you could add solar panels to operate this system, but BC electricity produces very little CO2 per kwh (we're talking a handful of grams per kwh), so running a heatpump on grid power would be very close to carbon neutral. Of course this does come with higher energy costs and higher initial purchase price, the energy costs could be offset by a net-zero solar system, but this further adds to the initial cost.

Will natural gas prices remain cheaper than electric into the future? I think that's a good question, it is known that the carbon tax will add $8.93/GJ in the year 2030 to the cost of natural gas, plus whatever the inflated cost of natural gas is at that time. Will electricity costs remain low or will they increase as well with the increasing demand from EV's? I'm of the wait and see approach on these topics, for that reason I think I'd go with the natural gas combi boiler, for about $5k you have a water heater and space heater in one, it's the cheapest option and the possibility would still exist to switch to heatpump down the road if the economics of electric were to change.

 

[peakbagger]

US carbon policy is pointing to switch US housing over to electric based heating, but buried in that assumption is that the electric heating is heat pump based so that the efficiency is much higher than standard resistance heaters. If the US is going to reduce carbon its likely that the price of natural gas is going to go up far faster than electric power. GIven the predictions for short term natural gas pricing this winter I think a lot of folks will regret using natural gas. At normal temps a heat pump based electric heating system uses about a 1/3 to a 1/2 less power than a resistance type boiler for the same heat output. With a new house you have lots of options and your utility may have incentives to go heat pump based electric. In theory spend the money up front to reduce the heating load and make sure the radiant tubing layout is set up for low temperature supply water. Ideally you want "home run" zones to each room. Low temp supply really opens up your options for a really efficient heating system.

Once you have a low temp supply system you are good candidate for an air source air to water heat pump or possibly geothermal. Air source is fairly new technology but finally US firms are starting to build and sell them. Here is one company https://enertechusa.com/advantage-air-to-water-heat-pump. The downside with these systems is that the efficiency drops quickly at the outdoor temps drop below 20 F. Generally the recommendation is to install an indoor thermal storage tank to decouple the air source unit from the actual heating demand and usually a backup electric resistance type heater is plumbed to the tank. The other aspect with an air source heat pump is that by adding a couple of water to air terminal units and getting cooling when you want it with no need for big ducts being installed. Geothermal that produces hot water (120 F) costs more up front but system efficiency in cold weather should be higher. If your design temps are above 20 F its not worth it but if you are down around 0 F than its worth looking at.

John Siegenthaler is a well recognized heating expert that is leading edge on the use of these units. Here is link to one of many of his articles with a sketch of how a system may be set up. https://www.pmengineer.com/articles/95000-john-siegenthaler-it-makes-a-difference . He has published several very good studies that show how a well designed low temperature radiant tubing or emitter systems have the highest efficiency. The article in the link uses radiators but in your case the radiant tubing zones would replace the radiator. https://www.pmengineer.com/articles/95000-john-siegenthaler-it-makes-a-difference. If you search for him he has multiple articles on these air to water heat pumps. When I do a search, Enertech has a couple of long videos on design but I have not viewed them. https://www.youtube.com/channel/UCWBPEWoys5HJwHfXnxCBXhA

 

[woodgeek]

Good advice by other posters, but I would add that radiant floor heating is not the best in a well-insulated, high efficiency home.

If this is a new build, you should be putting your $$ and attention into getting it above average insulation airsealing and windows, versus the barely code compliant build that most contractors crank out. If you do that, then your heating bill will not be a concern (mine on average is less than the cost of broadband and water). Look for a builder with experience in such buildings, not just greenwashing. In fact, most builders that are ready to build energy efficient homes would never consider putting in radiant.

That is the most 'future proof' solution for the house....hard to make thicker walls later.

Solar...price of solar is quite low. Incentives in the US are not that generous. If you have actually gotten quotes on solar, and don't like the payback, then great. If you are getting word of mouth from a builder that is not interested in energy efficiency, then you might want to talk to someone else. Ofc the solar resource in the PNW is NOT the best, and the grid power is very low carbon.

What is the issue with in-floor heating? Basically, as the envelope of the house gets better, less and less heat needs to be delivered by the floor, and so the service temp to keep the house in balance has to get lower (to not overheat the house). Everyone loves the idea of walking around on a floor heated to >80°F in January. That might work in a drafty house build to 1960 standards, but in a modern house the service temp might be just a few degrees above the air temp, and will actually feel cold underfoot! This will be doubly true during mild weather.

Radiant-Floor Heating - GreenBuildingAdvisor

Occasionally I wonder if I have some sort of masochistic streak — somehow enjoying the grief I get when bursting people’s favorite bubbles. I’ll brace myself for such a response to this column, when I point out why radiant-floor heating systems don’t make sense for new, energy-efficient houses.

www.greenbuildingadvisor.com

The other issue is one of control. The thermal inertia of the floor and the low heating temp make the time required to change the indoor temp (up or down) very slow. This slowness becomes worse as the weather gets milder and as the insulation improves. Net effect: you have to wait a long time to get warmed up if you house is cold, and you can never do 'setbacks' at night if you like sleeping cooler than at your daytime temp.

And then there is the fact that due to global warming, you will eventually want central AC. Doing a new build of a hydronically heated house in 2021 just means a costly ductwork retrofit at some point in your future!

 

[semipro]

I think what's above is some of the best, no nonsense advice I've yet seen here.
Given where you are and that you apparently do some heating with wood, and that you plan solar PV, I'd suggest you go all in on electric while improving the planned energy performance of your house's shell with a focus on air sealing then insulation plus energy efficient appliances/lighting. Use heat pumps for both water heating and climate control. Given your climate your main heating demand will probably be domestic water so consider that. I see no reason to add complexity by bringing in another energy source when you've got a great grid, solar, and wood.
This advice might change though if you don't plan for wood burning in the new place. I'd want some backup if the grid goes down and you may not be planning for battery storage for you solar, although maybe you should consider that.
As someone using the grid, solar PV with backup, wood heat, and an EV I get a enhanced sense of security knowing that we can live comfortably at home and travel without major concerns about supply chain and grid disruptions.

 

[peakbagger]

I wrote my post assuming that the house was in progress. If its not yet started then definitely spend more money to build a Passivhaus if you have a big checkbook and want green cred (for those who know what it is) or for more economical approach take a look at a "Pretty Good House" https://www.greenbuildingadvisor.com/article/the-pretty-good-house https://www.prettygoodhouse.org/ The pretty good homes being built in more severe climate in Northern New England typically do not use central heat, they just have few mini splits and small woodstove. One thing they do need is fresh air exchange system to exhaust stale air while preheating incoming fresh air. In general by trading off money up front to reduce energy loss the mechanical systems can be smaller and more importantly cost less to run in the long term.

Super energy efficient homes do not require much heat or cooling. As mentioned above radiant flooring may not be good fit for an energy efficient home. Folks like John Siegenthaler use radiant flooring in some specific locations but he has some very convincing arguments for not using radiant flooring in a typical home. He actually is an advocate for low temp radiant walls or ceilings with spot application of radiant wall mount emitters. They all have much faster response than radiant flooring and lower supply temps than a typical radiant floor. Unfortunately This Old House which is really a half hour long commercial received a lot of money over the years from the radiant heating industry and there is large generation of folks brainwashed into radiant flooring being the ultimate heat.

As for a future AC retrofit, on a small home, ductwork is rapidly falling out of favor. Moving air around just takes up way too much space for the amount of heat being moved around. Ducts need to be in the building envelope and that rules out attic or basement ducts so duct work ends up eating up a lot of interior space. The current approach is running insulated water tubing to room mounted air handlers that can heat or cool (equipped with drains). The bundle of supply and return tube plus a drain is far smaller for the equivalent cooling. On larger homes refrigerant flow devices with remote air handlers are even more efficient but the economics do not match for small home. In a Mc Mansion they are economical.

 

[iron]

Thanks everyone. A lot to unpack and digest here.

Last night, I was doing a decent amount of reading on GBA and kind of came to similar conclusions as you all are pointing to. However, one concern I have is that it feels like the heat pumps are not quite prime time yet and there is a lack of skilled HVAC techs that can do the job right. The town I'm in is small and I'm not sure of the availability of folks to do this kind of work. It seems like the go-to ATW HP's are Arctic and Nordic - both Canadian.

Also, I added this post to GBT with some additional numbers/background info:

Questioning using Radiant vs Alternative - GreenBuildingTalk - GreenBuildingTalk - Green Building Forums on Insulating Concrete Forms (ICF), Structural Insulated Panels (SIP), Radiant Heating, Geothermal Heat Pumps, Solar Power, Green Construction Pr

Not sure if that helps to clarify/illuminate anything. I've attached a sample report for an energy assessment performed for what's likely a similar house in the neighborhood (unsure of the windows comparison)

In general, I'm onboard with the idea of going to electric wherever possible to reduce the need for carbon fuels. Even if we don't do solar, BC Hydro is our energy supply, so we're ok on that front (minus future price spikes to cover huge infrastructure projects that are planned).

I fully expect the house to be at Step Code level 4, which is pretty close to a net zero house. So, I consider this to be a "good enough" house. The builder and I are exploring the idea of 2x6 walls vs staggered 2x4 walls. Based on the energy report, it seems that walls made up a good amount of the heat loss (as well as windows).

One doubt I have is the use of a heat pump water heater. I had installed one at our former home in Seattle and it was underwhelming to say the least. Water supply was inadequate compared to the old 50 gallon electric heater that it replaced. (https://www.rheem.com/products/residential/water-heating/hybrid/). So, unless the water heater is connected to the main heat pump unit (like a 4 ton system, or whatever), I have a hard time seeing this be useful in an area that gets to -20F at points in the winter. When the temp in Seattle dropped to 30F, the heat pump would run for hours just to heat water for one kids bath that was just used.

 

[ABMax24]

I'm a little bit bewildered by the estimated electrical consumption in that report, 7300 kwh per year is a lot considering natural gas fuelled heating and hot water. My house specs out very close to the average used in those reports, and I'm at 3000kwh per year, granted my dryer and stove are gas but I also have central AC that ups my usage.

I like your thinking on offset 2x4 studs, I'm hoping to build our forever house in the next 10 years and I think that's the route I'd go, spray in a couple inches of foam then fiberglass batts for insulation. I'd also at that time go to triple pane windows to decrease heat loss. There's a lot of merit to increasing insulation and spending money there to save by installing a smaller heating/cooling system and paying less for utilities over time.

 

[peakbagger]

Okay lots more data. If you get to -20F forget air source heat pumps. Geothermal is still an option but high up front cost and complexity. I am surprised a heat pump hot water heater did not make sense, of course if you didnt have heating source in the basement and were just using outside air that would be a problem.

General preference for me is 2x6 walls "flash and batt" (seal the cavity with foam then put in batt) with 1/2" iso board on the interior face under the sheetrock. That half inch of foam really makes a difference as it acts as a thermal break on the edge of the stud. Staggered 2 by 4s work but it can lead to wavy siding and interior sheetrock, the only way I would do it is if I foamed the walls to make them stiff. One builder I talked to advocated 2x4 walls with 2" of staggered Iso board on the interior. Note window framing is challenge with some of these framing techniques, the temptation is frame it out full depth but that introduces a poorly insulated thermal bridge. I have seen various solutions but they all are somewhat custom. One thing that Building Sciences pushes is minimal framing, Most contractors overframe. They build large window headers on non load bearing walls and do not sandwich in foam, they over build corners instead of install clips to anchor dry wall to. The thing that always show up as heat leaks is the box sills down low and the top of the walls. In the basement its best to spray the sill boxes with foam and keep going down over the sill onto the concrete. On the top of the wall and the second floor some folks recess the ends of the floor joists and put a strip of foam around the outer edges.

One thing that really makes a difference is specifying caulking at all wall all edges. Many houses including my own have a lot of air flow coming in from the floor plates and top plates. Also specify insulated enclosures for exterior wall outlets. When I had my blower door test down I was quite surprised on how much air was coming in through the outlets. I have seen reformed boots that are installed around the outlets but a squirt from the foam gun will seal up the outside of the box quite well (make sure the interior is masked off!)

So 88Giga joules = 83.4 Million Btus per year, 56% for space heating or for someone used to heating oil 360 gallons per year or 3.5 cords of dry wood a year Solar can contribute some but unless your utility has net metering its hard to justify currently. Net metering allows power stored up in the summer to be used in the winter. If you are in cooling zone it may make sense without net metering but looks like you are in heating zone.

 

[EbS-P]

heat pump water heater. I had installed one at our former home in Seattle and it was underwhelming to say the least.

So I have a an 80 gallon heatpump water heater two years old. It has heatpump only and a hybrid mose that will kick the elements on to meet demand. It is ventilated inside the building envelope. After giving it some thought I concluded this was the most efficient way to install it. Reasons were I need to run dehumidifier in the basement where it is installed. So I am getting free dehumidification when it’s running. Second it Acts as an air conditioner in the summer. Third the intake temps are always between 55-80 (higher the temp more efficient it runs). Fourth during the winter if I run a wood stove I am “heating” my water with wood.

At the same time we installed the water heater we put I. radiant resistive electric floor heat in a bathroom. It can have the warm under foot feeling if we leave the door open and set it to use the wall thermostat temp sensor not in the in floor sensor. It’s nice as it’s the furthest point in the house from the wood stove.

Nothing is more efficient than conservation and insulation. If you house is well insulated I think its probably ok to run a condensing gas boiler for in floor heat. I would probably install an appropriately (not too big) size variable speed compressor heatpump. It just makes energy sense if you have solar. The AC is a bonus. none of these styrene need to be designed to carry the entire heating load by themselves.

Having systems that can be installed and serviced by local companies can’t be overlooked unless you want to learn the ins and outs of the system your self.

Electricity is the future. You need to have a heating load calculation done before you can make any real decisions.

Just my thoughts
Evan

 

[woodgeek]

Thanks for the info. For some reason I had you closer to the coast. My bad.

I like the idea of staggered 2x4 walls a lot, and well made Canadian windows. Get a good gas boiler and a high SEER AC system. I"m personally not a fan of hydronic radiators in general, I'd consider putting water to air coils in the AC air handlers.

I would still push for a HPWH versus some crazy combi system. The tech has improved a lot in the last decade, and you should go big...I have an 80 gallon, 10 yo system and I'm quite happy with it. My main problem with the combi systems is they then size to HW demand (or have an indirect tank). The sheet you gave has a 10 kW design load and a 40 kW boiler. Yuck.

Agree that ASHPs are not there for you at this point, could always put a mini in somewhere to burn off some excess solar in the shoulder season, but it won't pay back against a gas system unless you consider the solar to be free. Alternatively, you could have a HP put in instead of a straight AC (for a small upcharge), and use it for heating at temps above 40°F outdoors (no defrost heater wiring required).

I think a little electric resistance heating in bathroom floor is a great amenity, but not a heating system.

 

[ABMax24]

Combi boiler tech has improved a lot in the last decade too, it's not really crazy and is actually an elegant solution to the problem, it's no different than an on demand hotwater heater with an additional heat exchanger that allows water/glycol of a hydronic system to be heated, allowing one variable rate combustion appliance to serve all heating loads. Navien for example has 200k BTU boiler that can output 210K BTU to DHW or 200K BTU to space heating and of course any combination in between up to 200K BTU total. That boiler also has a turndown of 15:1 meaning it can continuously output as little at 13,000BTU, which makes it very versatile for variable heating loads.

 

[iron]

Thanks all for the responses. It sounds like what I really need to do is to reach out to a specialist that works in passive house design (or close enough to it).

My limited reading tells me that while I think I could probably come up with a good wall system and heating/cooling elements, there's going to be a disconnect between my knowledge and what really works in practice. The one thing I really don't want to do is screw up some basic detail and then have some moisture problem that makes my walls rot away. Or, have a heating/cooling system that is overkill for the actual demands.

 

[begreen]

Has a geothermal system been on the list for research?

 

[iron]

Not really. My understanding is that it's no longer competitive when compared with the lower prices of solar.

 

[begreen]

I think in very cold climates it may still offer a better option than air source heat pumps, but maybe Mitsubishi will prove me wrong.

 

[Highbeam]

Resistance electric boilers are cheap, dependable, small, and maintenance free. I would install one even if you also choose a gas or heat pump solution for primary heating.

 

[iron]

Resistance electric boilers are cheap, dependable, small, and maintenance free. I would install one even if you also choose a gas or heat pump solution for primary heating.

Is there a way that you connect an ATW heat pump to radiant floor heating AND an electric boiler?

 

[semipro]

It sounds like what I really need to do is to reach out to a specialist that works in passive house design (or close enough to it).

Focus on the "close enough" part. Actual Passive House (i.e. haus) specs are tough to build and probably way overkill for your needs. You may freak out a builder by even mentioning it.
The advice above from @peakbagger to look into "Pretty Good House" standards is sound - a lot of performance for the money spent. I 2nd the suggestion that you start there.

 

[Highbeam]

Is there a way that you connect an ATW heat pump to radiant floor heating AND an electric boiler?

Absolutely, the electric boiler is just a flow through box with an element. When not heating because your other boiler is doing the job it just sits there allowing water to pass through. It can be triggered as a second stage for when the heat pump can’t keep up. Think of the electric boiler as your resistance strip heaters in a standard forced air heat pump furnace.

 

[EbS-P]

Is there a way that you connect an ATW heat pump to radiant floor heating AND an electric boiler?

I might consider this a first stage on a timer that could utilize any excess solar generating capacity. Use a gas boiler second stage?? AtWHP always seems appealing to me the. I try to figure out how to make it cool and I give up. Forced just makes sense as I think it can easily be updated with more efficient technologies in the future. This whole 410A phase out can’t be ignored but I don’t want to have one of the first systems with new refrigerant.

 

[ABMax24]

FWIW the OP lives in the region served by FortisBC, natural gas is $10.265/GJ delivered, electricity is $0.11601/kwh for the first 800kwh per month and $0.14118/kwh after 800kwh per month. Assuming the lowest electricity rate electricity costs 3.15 times as much as natural gas for the same unit of heat (assuming resistive heating), that's a sizeable difference on the wallet.

The energy report showed a usage of 88GJ per year for space heating, for $903.32 per year on current rates for natural gas, or $3209.37 per year on resistive electric heating. That is a very sizable difference in cost, unless CO2 emissions are the primary concern of the particular homeowner then these numbers play the primary role in determining fuel choice for home heating. My region is similar, except electricity costs more and natural gas costs less, natural gas fuels every heating appliance possible in my home and that decision was made solely on the basis of cost.

Resistive electric heating makes absolutely no sense in Western Canada from an economic perspective,. Want cheap heat with the option for backup if utilities fail? Install a cost effective condensing combi boiler or condensing gas furnace and use the rest of the budget to install a nice wood stove. If someone really insists on spending a bunch of money on a heating system then install a ground sourced heat pump, air sourced units aren't viable here.

 

[iron]

FWIW the OP lives in the region served by FortisBC, natural gas is $10.265/GJ delivered, electricity is $0.11601/kwh for the first 800kwh per month and $0.14118/kwh after 800kwh per month. Assuming the lowest electricity rate electricity costs 3.15 times as much as natural gas for the same unit of heat (assuming resistive heating), that's a sizeable difference on the wallet.

The energy report showed a usage of 88GJ per year for space heating, for $903.32 per year on current rates for natural gas, or $3209.37 per year on resistive electric heating. That is a very sizable difference in cost, unless CO2 emissions are the primary concern of the particular homeowner then these numbers play the primary role in determining fuel choice for home heating. My region is similar, except electricity costs more and natural gas costs less, natural gas fuels every heating appliance possible in my home and that decision was made solely on the basis of cost.

Resistive electric heating makes absolutely no sense in Western Canada from an economic perspective,. Want cheap heat with the option for backup if utilities fail? Install a cost effective condensing combi boiler or condensing gas furnace and use the rest of the budget to install a nice wood stove. If someone really insists on spending a bunch of money on a heating system then install a ground sourced heat pump, air sourced units aren't viable here.

I think my current train of thought is that I need to improve insulation and air sealing to get closer to Step Code 5 or Passive House certification levels. There are a lot of rebates out there from the local utilities that will reward you for achieving higher standards, so the longterm play seems to be this approach. If I can get the house down to a point where minimal heating is needed, then electric + solar can/will make sense. Also, my understanding is that NG prices in BC and Canada writ large are going to increase significantly in the future. And yes, part of me wants to take this hopefully once in a lifetime opportunity (i.e. new home build) to do the right thing, even if it costs a bit more directly to me.

 

[iron]

So, we are now aiming for Step Code 5, which is shown as this:

Step 5: Net-Zero construction ​

• 1.0 Air Changes per Hour (ACH) – all of the air leaks out 1.0 time per hour
• 15 kWh/m2/year Energy Use per Year – This means the cost to heat the average 2000 sq. ft. home would be about $230 each year*
  • This is about a 70% improvement over Step 1 and is almost the same as the European Building Code standard used for many years in many countries. The main differences are that we require solar or other sustainable energy systems to offset energy usage and the Europeans require 0.6 ACH. Part of the reason for this is that less mould will form with a less drafty house, decreasing the number of health risks like asthma and increasing the comfort of the home

The biggest thing we're working on is wall design. I think we generally have thermal bridging, foundation, and basement slab sorted out. Since we're late stage in the game for implementing this higher performance standard, we're not going to be able to use super thick walls like you would on a Passive House. Instead, I think our best compromise is the following: 2x6 with Roxul batt insulation, plywood, air barrier, 4" of Roxul Comfortboard 110, nailing strips, and rain screen (mix of stone and Hardieboard). My builder is a little concerned about the 4" on the outside of the plywood, not from a construction standpoint, but from an air movement standpoint. I understand, from my reading, that this would be an issue if we were using XPS or some other rigid board, but with Comfortboard, this is air permeable and, in my view, intended specifically for something like this. Any thoughts on this proposed wall construction? I've attached the City's design criteria for temperature.

Second big thing is the wood heat. In reading more about wood heating with Passive Homes, or really airtight homes, it seems like a simple OAK is not good enough and that we would need to be looking for something that is fully air sealed. I read something to the effect that EPA certified stoves and fireplaces, while great, never fully shut off the air so there is always a leak. Thus, I am looking for recommendations on fully sealed units (ideally some kind of fireplace, but I'm suspect that this is possible). Ones I have seen mentioned on other forums include:

Stoves for passive houses

In order to operate in “passive houses” or in “high energy efficiency” homes, fireplaces and stoves always need an air inlet from the outside

www.mcz.it

Wood burning stoves - Large selection of quality stoves - RAIS

New standards for how you heat your home with fire stoves. We have a wide array of unique wood burning stoves drawn and made in Scandinavian design – RAIS

www.rais.com

I suppose there is always the possibility of just cracking a window when starting (hopefully only then), but that seems to defeat the purpose of airtight homes to me.

Thanks

 

[begreen]

Outside air on some stoves is sealed and on others it's more open. The main issue you may find with wood heat in a well-insulated home is that it can be too much heat. Do the heat loss calcs carefully and then factor in all the inputs from lighting, refrigeration, bodies, etc. You might be surprised how little heat it takes to maintain a comfortable 72º when it's 20º outside.