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Water Heating Dilemma

by Chad Ludeman on February 8, 2008 · 30 comments

in Building Science,HVAC

I have been doing a bit of research over the past few weeks on the most efficient method for heating both our radiant heating system and domestic hot water. This is not meant to be an exhaustive account of that research but I am conflicted as to the best option. In the end we will most likely pay an experienced HVAC contractor to design the most efficient system for our needs. Below is a basic account of the pros and cons of the various options I have looked into so far.

Gas On-Demand, Boiler or Storage


  • Very efficient
  • Lower cost to operate than electric


  • We want an all electric home to allow for zero-carbon conversion in the future
  • We want an all electric home to reduce utility hookup costs and delays from the gas company
  • The gas supply lines in Philly can be too weak to sufficiently supply some on demand units

Electric Tank


  • Low installation cost


  • Not very efficient
  • High operating cost
  • Must keep tank heated at all times

Electric On Demand or Boiler


  • Very efficient
  • Small space requirement


  • Capacity can be limited
  • High current capacity needed may be too much for normal 200 Amp service

Electric Heat Exchanger / Storage Heater Combo


  • Extremely efficient
  • Cools and dehumidifies the surrounding air


  • Space requirement for both tank and heat exchanger
  • The heat exchanger will be taking heat from the indoor air during the winter in order to heat the floor which, in turn heats the air again. Sound like a vicious cycle to anyone?

Solar Thermal System


  • Extremely efficient
  • Renewable and clean energy source reduces the size of PV system needed to achieve zero carbon in the future


  • Installation is cost prohibitive on our budget
  • A large storage tank is needed somewhere in the home
  • A backup heating source is still required

This is not meant to be a discouraging post. We will prevail but this is an example of the challenges of finding the most efficient and cost-effective system for our affordable, green homes. You hope that there are easy and straightforward answers out there that can be easily found but it is not always the case. I have calls out to a few people who are looking into the best solution but if anyone has any ideas grounded in reality, they would be much appreciated. As I said previously, we will most likely invest in a professionally designed system to ensure we have made the best choice from a development and long-term standpoint for the homeowner.


American Council for an Energy-Efficient Economy – Water Heating 

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1 Shawn February 9, 2008 at 12:34 am

A friend of mine went on-demand electric…I believe his (somewhat large) home required two 60-amp circuits.

It seems like the electric on-demand is the best option, considering your priorities. You may need a bigger service, but that doesn’t seem like a very high bar to clear.

Here’s a little piece I wrote on these units a while back:

The design is pretty sweet!

2 chad February 9, 2008 at 3:59 am
3 Shawn February 9, 2008 at 5:43 am

Oh, now that is funny! I need to check with my friend who actually installed one of these units and see if he likes it. Will report back.

4 Shawn February 9, 2008 at 6:13 am

Hey Chad,

I posted a follow up on my friend’s experience using the water heater listed in your post. It’s on my blog:

5 Emily & Rod February 9, 2008 at 6:35 am

We are also in planning stages on building a green 1000 sq foot house in BC. We are new to this site so haven’t really gone through previous posts yet. This is where we are for heat:

- We are either electric or off-grid, and adamantly against gas for many reasons.

- Our first choice for heating is geo-thermal. It is prohibitively expensive for us at this stage, but an option for later on. Because of this, we have decided to go with an on-demand hot water heater. Up in the air on open or closed radiant system, but hope to use an open system that will cover the floor due to our low heating needs. Conversion to geo-thermal in phase 3 wouldn’t be as painful this way.

- I have heard from several sources that people are using industrial sized on demand heaters for their open systems.

- We are including thermal mass and passive solar as part of our heating (and cooling, sortof) plan.

- Our ace in the hole is our high efficiency wood stove. This may not be appropriate for your location, but for our location, cost, availability, and the lovely dry heat are a no-brainer for us. Until we get the geo-thermal.

6 Gary February 9, 2008 at 2:58 pm

I don’t mean to rain on your parade, but when you include electricity generation in the picture, there are no efficient or clean electric solutions. One KWH generated at a typical 30% efficient coal plant results in 2 lbs of CO2. Most of our power comes from coal plants.

By comparison the CO2 generated by a gas furnace or boiler to produce the same 1 KWH of heat energy is 0.5 lbs — four time cleaner.

The idea of going all electric so that you can later add solar electric to go zero carbon is admirable, but have you looked at what that solar electric would cost to install? Believe me if you can’t afford solar water heating, which is efficient and relatively cheap, then you can’t even begin to afford a PV array that would power your house. If your house used 1500KWH a month of electricity, this would require and about 10KW PV array. The cost for this would be pushing $100,000.

If you want your house to be energy efficient and to have a smaller carbon foot print, then emphasize these:
as little space as meets your needs, very good insulation, very good sealing, very good windows, passive solar heating, passive cooling, efficient appliances, efficient lighting, and solar water heating.

Most people spend most of their energy on space heating and cooling –the way to minimize this is to put money into the house envelope (insulation, sealing, windows), and into good design of the house (passive solar and passive cooling).

Have a look through the Solar Homes part of my website — you might find some helpful ideas there.


7 chad February 9, 2008 at 7:50 pm

Shawn – Thanks for the research on this model. It’s cool that we found the same model on our own searches.

Emily & Rod – Good to hear about your similar project. We briefly looked at geothermal also but could not afford either. It is easier to justify one geothermal system for mutliple units like in a condo building as a developer. The problem I have with the industrial on demand units is that they require a lot of power and many need 3 Phase power which would be cost prohibitive (and a bit crazy) to run in such a tiny residence. Multiple, small on-demand units may do the trick though. I really like the wood stove idea and would love to put one in a future project.

Gary – I understand your concerns with all electric power. There are options for homeowners in Philly to get their electric from wind or solar now that we would take advantage of. Ultimately it would be up to the homeowner to maintain this renewable energy source.

If you read some of the previous posts you’ll find that we are indeed focusing our budget a better envelope and all of the other items you mentioned. These are harder to upgrade and the passive elements are usually impossible to improve once a house is complete. This is also why we feel it is important to install the most economical HVAC system that can easily be tied to solar PV and/or thermal systems in the future.

We can not afford solar in our $100K budget, but our hope is that the homeowner may be able to afford it as an add-on in the future. With our small and energy efficient design, I think we would be able to get away with a 3-6KW PV system that is tied to the grid and provides net zero energy over a 12 month period. The hope is that incentives will return to PA and Philly and this will become a net cost of $10K – $30K for the homeowner. This then becomes a decision between having a nice car or having a zero energy home and riding a bike more often. In other words, it makes the decision reasonable for the homeowner.

8 lavardera February 10, 2008 at 6:33 pm

Would a high effeciency gas fired tank water heater be too much of a compromise? I’m just thinking lower first cost, possibly lower to operate, and open to solar hot water preheat – which would be less expensive to add in than a PV system for an electric heater.

If you did not have gas at the street in Phila. it would be harder to rationalize, but you do (I know – dealing with the gas company is probably the worse of the two evils).

9 chad February 11, 2008 at 1:54 am

I need to look into what it would take to install a system that a solar thermal array would be able to be installed to in the future. It may be as easy as an 80 gallon storage tank/heater with supplemental electric water heater. If we did it correctly there would be minimal extra cost compared to a traditional installation and all that would be required in the future is the installation of the solar thermal panels on the roof by the homeowner.

I really don’t want to go with gas due to both the potential issues with the gas company and the inability to convert the home to zero carbon in the future. Finding the right electric cooktop, not the water heater was my big challenge to overcome in this decision…

10 Gary February 11, 2008 at 2:21 am

If you want to be able to add solar water heating easily in the future, then some of the things to think about are:

- Figure out where the collectors would go — if there there is no good place for them with good southern sky exposure for at least 6 hours a day, then consider rearranging the roof to make a good space.

If the hot water tank is currently in a place that makes for a very long or awkward run from the collectors to the tank then consider moving the tank.

- Install the plumbing runs between the between the hot water tank area and the attic so that this won’t have to be done later. This is a minimal cost, and saves lot of hassle adding them through existing walls later.

- Since most solar water heating system will want to have a 2nd tank for solar heated water storage, allow room for the 2nd tank in near the electric hot water tank.

I can see the desire to eventually be able to convert the house to a zero carbon house, but maybe that should be weighed against the considerably greater GHG emissions that the all electric approach will result in over a gas approach in the time period before the conversion to zero carbon is made (if ever).

For a family of 4 using 60 gallons of hot water a day, this is about (60 gal)(120F-60F)(8.3 lb/gal)(1 BTU/lb-F)(365 day/yr) /(0.95 efic) = 11.5 million BTU/yr or 3360 KWH a year, with 6600 lbs of CO2. The NG approach would cut that down to about 1890 lbs CO2 per year with an 85% efficient tankless gas heater.
Just a thought.


11 chad February 11, 2008 at 4:24 am

Great things to consider Gary, thanks! We do have a good south facing spot for the collectors on the top of the roof and there will be very short runs since all of the hot water needs will be centrally located in the core of the home.

Due to the small, 1,000 square foot size of the home and only 500 sf of radiant, I hope that only one tank will be necessary with a supplemental on demand or similar unit. Storage and utility space is at a premium in the home as it is. It will most likely be a family of two or even just one in these homes also which should reduce the overall hot water demand.

I plan to get our electric service from renewable wind power ASAP when building the homes and see no reason why the homeowners would want to switch as it will only cost them an extra $5-$10 per month.

I’m still not convinced that solar thermal is cost effective in the long run for these homes though given the local climate and maximum need for solar generated heat in the winter when the supply of direct sunlight is least.

12 Rob February 13, 2008 at 7:56 pm

If you are truely interested in zero-carbon then check out thin film solar cells. It appears as though they will eventually replace traditional PV panels as they are currently cheaper and more efficient. An example would be .
And from what I remember while working on the Solar Decathlon house while I was a student at Virginia Tech, the solar thermal was less energy efficient than the PV panels. The engineers determined that we could use the same amount of space for PV panels and generate more than enough electricity to use a conventional water heater. This was in 2002 though, times may have changed.

13 Gary February 13, 2008 at 9:58 pm

Rob — Solar thermal panels are 40 to 60% (sometimes even more) efficient.
Good PV panels are about 15% efficient.

Solar thermal panels are both more efficient and cheaper.


14 chad February 13, 2008 at 10:27 pm

Interesting discussion here. I am familiar with Nanosolar and think they are about 19.5% efficient.

I have heard arguments on both sides of the solar thermal issue. Some say it should absolutely be done before thinking about PV while others disagree. The fact that there can be too much output in the summer and not nearly enough during the winter (especially with radiant) still concerns me. I am not an expert on this so I may still be misunderstanding the issues.

These issues are always dependant on location as well. What works best in Vermont is going to be different that what is best in Philly or Georgia…

15 Shawn February 14, 2008 at 12:14 am

Hey Gang,

this is a pretty good resource – it’s in my home state (Oregon), so you can’t really go to the workshops, but, there is some excellent data on Solar.

16 Gary February 14, 2008 at 3:13 am

This Wikapedia description talks about efficiencies for Nanosolar panels all the way from 6.7% up to 19.5%:
Even though the company is said to have started producing panels, they have not said themselves what either the efficiency or cost is. But, it does look promising after near to 50 years of “dirt cheap PV is just around the corner” stories — hope it happens.

If you compare solar thermal panels and PV panels on the same basis that PV panels are rated, which is output in full sun, they come out like this:

PV panels from a bunch of big suppliers retail for about $5 per peak watt of output.

Solar thermal panels from a bunch of not as big suppliers and rated in the same way retail for about 50 cents per peak watt (see below for where this comes from).

So, solar thermal collectors are about 10 times cheaper per unit of energy produced.

Its true that solar space heating panels only have use for about half the year when you need heat, so divide the factor of 10 in half if you like for space heating — its still 5 times more cost effective.
Solar water heating is year round, and this does not apply.

I’ve never been able to figure out why solar electric gets so much attention when a) its so much more expensive, and b) we use so much more thermal energy than we do electric energy. Puzzling.

One reason that I am a big fan of solar thermal energy is that it is very low tech and and building solar thermal collection systems is well within the talents of the average DIYer. The solar thermal panels that I use to heat my shop cost me $2.50 per sqft in materials — a tenth of the price of commercial solar thermal collectors, and a hundredth the cost of heating with PV!
These panels pay for themselves every year in saved propane.
The solar water heating system I use to provide part of the heat for my house, which includes thermal storage and a new radiant floor cost me a bit over $4000, and has a pay back of 4 to 5 years.
All described in gory detail on in the space heating section.

This same simplicity of design for solar thermal offers opportunities to integrate collectors with new construction in ways that save money. A carpenter with very little additional training can build a collector into south facing wall for very little more cost than the wall itself.

The 50 cents per peak watt calc is based on commercial solar water heating panels at $25 per sqft, 60% efficiency, and 1000 w/m^2 sun (same as PV is rated for):
1000 watts/m^2 = 93 watt/sqft

Output/sqft = (93watt/sqft)(0.6 efic) = 56 watts/sqft

Cost per peak watt = ($25/sqft)/(56 watts/sqft) = $0.45/watt

Note that efficiency on solar thermal collectors varies with ambient temperature and storage tank temperature, but the 60% is what a good thermal collector can do in moderate winter conditions and producing storage tank temps that are compatible with radiant floor heating.


17 chad February 14, 2008 at 3:14 pm

Good stuff Gary. I am definitely going research this further on your site and others before my first meeting with the mechanical consultant next Wednesday. I want to make sure we make the best decision for future solar add-ons for our buyers and the solar thermal issue is critical to the entire mechanical design. Also, if by some miracle we can squeeze an extra $5K out of our construction costs then we could afford a nice solar thermal system in the final, stock home.

18 Rob February 14, 2008 at 3:21 pm


Thank you for your corrections to my statements, clearly you know more than me about solar thermal. Looks like I have some researching to do.

On that note, Nanosolar, as stated in this article , believes that they will be able to produce electricity for $1 a watt or about equal to coal produced electricity. That also is right in line with your figures for solar thermal I believe. Also, as stated here , Nanosolar has already sold all of their anticipated 2008 production.

Also of note if you were using the 8000 degree days of Montana as a comparision, Philly has less that 4000 degree days. So that would factor into the need for solar thermal as well.

All in all though, you make excellent points and I will have to look into the DIY possibilities of solar thermal.

19 Mark April 4, 2008 at 12:15 pm

Are you including the basement in your square-foot size calculations? We chose the building site specifically so we could have a walk-out basement with a bedroom and library room, lots of windows, precisely because of my interpretation of the LEED regs: square-foot calcs. need to take into account all space that is even potential living space, even the basement, which is required to be heated under building codes. We are even using the attic space, and not having one. With SIP construction and raising the walls 3′, we are able to make the space that would usually be wasted space into living space with minimal additional cost. With a footprint of 18′ wide by 50′ long, we are able to take advantage of lots of windows for passive solar and utilize the entire inside space of the house which might, under other calculations/interpretations be a 1000 square foot home into a 4-BR 2400 square foot home.

So back to my question: are you including your basement in your square-foot calculation? I think you should…

20 chad April 7, 2008 at 1:17 pm

There is no basement or attic in our design due to budgetary reasons. We are using a slab on grade foundation.

21 Ted May 6, 2008 at 3:53 am

Sorry, I’m a bit late to the conversation. Just discovered your interesting blog. All good stuff!
A couple comments:

Electric storage water heaters are quite efficient, up to an energy factor of 0.95, which is vastly better than any of the (affordable) gas water heaters. Also remember the installation cost differential. Electric heaters are plug and play. Gas requires flue and combustion air vent installation

On solar hot water- I often hear the comment about what to do with excess summer production. Note that the locations where solar thermal is most popular are hot, sunny climates, where they likely have excess production year round. You just have to design the system properly.

Also, as noted by another poster, solar thermal can be very cheap and effective. Another group in Philly showed the efficacy and costs of different designs. I can’t find the link at the moment, but was talking with Nick Pine who has all sorts of ideas on low-budget/practical solutions, and he referred me to that project.

Was talking with PECO the other day. Their electric is 70% nuke. Whether you like it or not, that greatly reduces the CO2 in the comparisons. Also, for a cost analysis, remember that if you heat with electric, you get RH discounted rate in winter, which is only 7.029 cents/kwh after the initial 600kwh used. This makes even electric resistance heating much more affordable, but still not as cheap as NG at today’s rates.

For the long term, you’d be better off with an efficient heat pump in a small structure like this. A decent one costs only 2/3 as much to run as NG, but still doesn’t resolve your need for hot water. And, the first cost would be several times that of a simple electric water heater.

If I were doing this for my own projects, with your constraints, I would go with home-made solar space heaters supplemented by cheap electric baseboard heaters and a Whirlpool EnergySmart electric water heater. When my budget allowed it, I’d add solar hot water.
If I didn’t have as strict a budget, I’d get a high efficiency, two stage heat pump, plus use good passive solar design and solar space and water heating.

22 chad May 8, 2008 at 7:14 pm

Another excellent comment from Ted. I’d be very interested in that solar thermal link if you find it. I hear you on the baseboard heaters.

At this point we are all married to the idea of radiant heat, both for the efficiency and the marketability of it. I have cold concrete floors with forced air and would love to have radiant if possible. This is seen as a premium feature in Philly, so the fact that we can pull it off affordably is a no-brainer for us.

Thanks again, and I look forward to more of your comments in the future.

23 Ted May 9, 2008 at 12:07 am

Aha, found the solar hot air space heating system:

This might be a nice supplement for heating.
I agree about radiant. It really is a great system. I just wish there was a good heat pump setup for heating water for the radiant loops. Geothermal does a good job for low temperature radiant, but that’s no in the cards for a low-budget project. Ultimately, the solution you’ve picked seems like the best choice given the constraints.

24 Sean May 27, 2008 at 5:44 pm

Really interesting thread..and one on which I might actually be able to offer input. First, Gary, I am right with you on the carbon thing: I have sought as many ways as possible to get us down to where we need to be. The following scenario is for a 1350 sq foot twin home divided into two apartments and assumes we will add 6K of PV in 2009, which we hope will eliminate the carbon issue for us.
Ok, here goes: L and R Associates in Hatfield is a local distributor for Wirsbo radiant floor products and is where I took my radiant heat training. While there training I became intrigued with instant Seisco Electric water heaters. What interested me was the Seisco ability to “ramp up” into the on mode, negating the need for grossly oversized electric services. With 40 amps of draw, the smaller unit we were considering for our 725 sq foot apartments still required a minimum of a 125 Amp service. Obviously, I was concerned that “Ramping up” would cause slow response in a device already seen as unresponsive by many in the field. But Seisco offers persuasive arguments in their site and what I thought were good figures to back it up upon inquiry.

After looking at Seisco figures we decided it was possible to pair the seisco with a solar water collector, a tank with TWO heat exchangers, and, TWO sets of tubes in our basement floor: one set of tubes to heat the mass, and one set of tubes to draw heat from the floor, reducing the use of the electric heater considerably (in our crusty makeshift model).

The Scheme works like this. The basement floor is not treated as part of a living space: it is seen as part of the HVAC system. Normally a radiant floor heated to 105 degrees max and preferred at 97.5 The floor is normally engineered to take in 120 degree water and drop about 20 degrees as it goes through floor loop. So in our model we hook up one exchanger in the solar hot water tank to one set of tubes with a 10K sensor and a pump. the tank sensor is set at 130 degrees and forms an “and” gate with the floor sensor, if the floor is less than 105 degrees. In this instance, the pump pushes water out to the floor and loses its heat in the concrete, in effect, extending the size of your hot water storage for the cost of a second heat excahnge coil, a pump and some extra HePEX. When the floor reaches 105 degrees OR the tank temperature drops below what you want for your domestic hot water temp (115), the pump shuts off.

Then, on the heater side (or so our theory goes), when the thermostat calls for heat, the first thing the system does BEFORE THE HEATER IS TURNED ON is expose all radiant surfaces in the system to the heated water in the second loop in the concrete. This happens only if it is higher in temp than a sensor at the intake side of the electric heater. In this fashion, the water rolling through the concrete floor loop gives off its heat when it mixes with water from the other loops. When the pad drops to 97.5 in heat, the pad loop closes.

One of the possibilities here is to “overheat” the basement floor up to as much as 110 degrees if it is appropriately segregated from the living space. In this way, more heat is stored in it. In the event it was a living space, you could lay sleepers and another floor on top of them and drop a simple vertical duct from the floor leves in the living space down to the pad surface and use the rising heat to advantage and to create some degree of convection in the house.

Where I am with this is I am confident on the size of the seisco heater, and have controls down. I have yet to ask my superfriend, Brendan O’Riordan, a GSK engineer and a night student at Drexel Architecture, to sit with me through the calculations for the solar loop: We need to get sizing for the collector, tank, exchangers, and floor tubing, relative to the volume of the rest of the system. We also need to look at the optional duct and or fan drawing heat from the pad.

As regards gas boilers, hands down Bederus is the best of the best I have used. I understand it does not apply here, however, you might look at what features they offer in the hope of finding someone else who can give you the bang for the buck you need.

I also heard the comment about having enough roof space and wonder if the house is structurally capable of handling a roof deck, with an eye toward creating a solar panel canopy over a future deck.

At the moment, though, I have to go make money. So I leave you all to ponder choices. I am sure you will find a good combination

Ok, I gotta go make some money

25 high end radiant installer October 15, 2008 at 11:56 am

You are all on the right path, But Some of you havent been doing your homework.

Need hot water? use whatever current water heater you have allready and simply add a solar drain back system to it. It has been designed so anyone can hook it up. its easy and comparitivly cheap. Another route to try would be a wood fired boiler. with the newer triple pass designs that are out now they cannot be beat for the eco conscious person. oh, geothermal can heat both domestic and space heating water if its sized right. As was stated earlier by one of you (which was the best sentence I read on this site so far) INSULATE!
There is nothing more important than haveing a well insulated draft free home. consider even spray foam! If your feeling extra crunchy you can evan get 99.8% organic spray foam called Biobased 1401 which uses water as the propellent medium.

26 high end radiant installer October 15, 2008 at 12:04 pm

P.S. Stay away from propane and natural gas. the united arib emerates have stated that even if the started building new production facilities today and kept building them as fast as they realistically could, given the current rate of population growth and consumption habits of people worldwide the demand will no longer be able to be met as soon as 2016. go with oil fired and make your own biofuel.

27 Sean October 16, 2008 at 12:46 am

As an energy rater and auditor my sense is that a sense of timeline is appropriate here, as well as an understanding of NEC 2008 AND a sense of world market conditions AND a sense of local gas company capabilities. Lets work backwards in that.

First, where you are, PGW is capable of delivering what you need to power a Rinnai or Bosch or Takagachi unit that modulates between 40,000 and 120,000 Btu hours. If this were not the case a 120K boiler in a large home would die. Because of your square footage and your expected occupancy of 3 people with perhaps a max capacity of 6 people overnite in sleeping bags or on futons a simple low end gas unit would function without challenge with an EF of .85 to .91 as compared with a storage unit with an EF of .56 to .61.

We function here with three people in a duplex using 4100 gallons of water a month which breaks down to 45 gallons per person a day, or 1/2 of the 90 gallons a day used to size septic systems. We presently do this without graywater through correct placement of good shower heads, quality aerators, frontload Whirlpool duet sport washing machine/dryer combos, and a quality Danby dishwasher with water management build in. Your Hot water load can only be as large as the largest gpm of the components which operate downline from the heater! The heater must be matched to demand. GPM Demand can select the heater for you.

While there are those as above who will decry the world natural gas market as suspect, vehicles play an equal part (google Quads 2006 EIA) in the world condition. We will be forced to bring vehicles onto the grid to recharge them in the next 10 years, placing pressure on the grid and creating a demand for microproduction on eveyone. This is why the state and the feds are now reincentivizing existing home efficiency and tying it to solar rebates.

At present rates UNCLE SAM can deliver to you a $2K tax credit for installing an evacuated tube solar hot water heater (NO DRAINBACK IN THIS LATTITUDE!), and Uncle Ed can deliver you $1K to 1.5K. Average cost on an existing home would be $7K. In new construction kill it by 20%, leaving you at 5600 less 3500. If you used it to fill two tanks, one for hot water and one for heat, you could negate your heating bill except for DEC 15 to Mar 15.

All these difficult decisions aside, your obvious weaknesses in a REMRATE model are in windows and doors. As a LOW BUCK approach to managing fenestration loss, I prefer built in window treatments with a built in ceiling on the treatment to block room heat from leaving (remember the first law of thermodynamics?) and to capture heat before it arrives in a conditioned space. Even with windows at say .30 U value, when converted to an R value you arrive at 3.33. When you add an appropriate treatment you can TRIPLE the R value of the opening, drastically affecting the effect of the opening on the whole. My point here is that in modeling, where windows (even in passive solar conditions) often create more loss than a .56 to .61 hot water heater uses in a year.

28 tom toolbag January 6, 2009 at 6:12 am

I like the idea of running extra pipe in the slab, I had thought of something similar, running an array of pipes like a huge manifold on the ceiling, mounted about 1/2″ to 1″ off of the ceiling to capture the heat at the ceiling, but the temps wouldn’t get high enough to use as a source for hot water(showers) but could pre-heat for a w/h. Why not have a holding tank with the extra pipe(that runs right beside youheat pipe) running to it’s exchanger from your living area, and also an exchanger pipe running from your boiler circulating when the boiler runs for heat. If need be, you could add on an electric on-demand w/h if the temps are out of the comfort range.

I agree with the statement of: INSULATE, it’s the easiest way to gain the most. The passivehouse homes prove this.

I also agree with window covering point. Using thermal curtains that are affixed by magnets will cut down on heat loss, and it can be done pretty cheaply. The most disappointing 2 things in the building industry in my life(42 years) are windows and doors. Seeing an energy efficient home and all the meticulous work that went into, with the same old energy losers for doors and windows really irks me. There was a good show on the Discovery-Science channel around new year’s called Ecolopolis. There was a guy on there that was trying to develop a replacement for window glass using allurgen? material that NASA uses for insulation on spacecraft. No conductivity of either hot or cold temps, and was fairly transparent. The big problem is that it is very brittle.

One last thing, there are some nice boiler systems that are fueled by bio-mass. Wood pellets, corn, and even oats. Oats sounds pretty reasonable because of the cheap price and the fact it’s not a food grain per se, and isn’t fed to food chain animals(cows or pigs)but mostly to horses.

29 Kris November 28, 2010 at 9:58 am

Still making my way through all your posts, but I still haven’t seen any energy calculations for how many BTU’s this house will use. We completed our calcs very early in our design process so that we could answer questions about what water temp the floors will require. SIP panels and super insulated structures allow for much lower floor temps than is typical. This can have a big effect on what options will work for heating the water. Also radiant floor systems work most efficiently if the equipment is carefully sized to allow them to run constantly. Oversizing a system leads to inefficiencies and extra cost.

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