Hi- I'm a contractor retrofitting my own home on Cape Cod. It's a balloon framed, two floor, gable (cape) style with shed dormers (upstairs) on both sides. The home was built in 1925 and I've gutted to framing- replacing windows, electric and blowing in closed cell foam r-8/inch in the 2x4 wall cavities. Anyways, I'm having a gas line brought to the home and I intend on putting a new HEATING and possibly air conditioned system(s) in the home. THe old system is an oil fired steam system with cast iron radiators (which is being removed). I know there are endless options, but aside from buying a wood stove and using the existing chimney, what is the cheapest and most efficient new heating system I can install? here are the options I've considered- 1. direct vent gas furnaces 2. ductless splits 3. ducted central gas furnace, A/C down the road 4. Gas-fired cast iron stove Thanks Mark

Ductless minislits should be the cheapest and about the most efficient if the house has a small enough heating load. One benefit is that solar PV panels can be added to supply the "fuel". Have you, in your renoveation insulated and sealed the basement to keep cold air and moisture out?

Thanks Bob, that's what I was thinking. Yea the house is air sealed as they sprayed the perimeter joist bays and I am due to insulate the basement joist bays in basement and ceiling with open cell. Good idea with PV, I wish but my roof is facing east and west

If you go with the ductless splits, you won't need to spend the money bringing a gas line to the house. You could also get one of those efficient heat pump water heaters that use electric energy a lot more efficiently.

If I were in your shoes, I'd probably want to go the all electric route seeing solar energy is starting to look more attractive as the world's best renewable energy. As the technology gets better, it's probably going to become easier to produce it on site negating the need for natural gas hvac.

How many square feet is your house? You said that the home is air sealed.  Do you have a ventilation strategy?

the house is ~1000sf, three small bedrooms upstairs and open floor plan and half bath (to be) downstairs. I'm biting the bullet with a gas line because local gas Co, National Grid, only charges $500 for up to 30'. On-demand gas h2o heater, gas range, gas dryer. I'm thinking of using a air exchanger for ventilation i'd really like to find a way to do it through bath vents though...

Are you buying a new water heater as well?

Maybe you could heat with hydronic and put it in a few radiators and an indirect water heater tank. Very comfortable, not as dusty, and cheap to operate.

Panasonic makes balanced spot ventilation systems that bring in tempered make up air right to the same room.

How airtight is the house? Have you had a blower door done recently? You have good shading? I bet that you have an extremely small heating and cooling load and you could get by with a VERY small system. For cooling, I bet you could get away with one or two ductless minisplits.

All successful & comfortable heating solutions start with a room-by-room heat load calculation, even when the loads are quite small (as will surely be the case here.) It's not rocket science, but it matters. Even a simple I=B=R method spreadsheet (pretty quick & easy as a DIY) is going to be way better than WAG.

Even though gas is available and cheap, even with code-min windows the heat load on this place is going to come in well under 20,000BTU/hr, and the upfront expense of a hydronic solution compared to mini-splits is still large. Spending the hydronic-system money on U0.20 or lower windows (particularly for the bedrooms) would make the room-to-room temperature differences of going with mini-splits much lower, and provide more comfort overall. The upcharge of heating with mini-splits vs. condensing gas is small in MA from the bigger electric utilites, and mini-splits can even be cheaper heat with than gas if you are served by some of the lower cost municipal power companies. Depending on the layout upstairs and the room-by-room heating/cooling loads you may be able to get by with a single ductess head up stairs, or a tiny split-ducted mini-split head to better distribute the heat/coolth. The open floor downstairs would probably do fine with a single mini-split head, even with code-min windows in the main area, U0.20 windows on any doored off room.

Whatever the R/inch, closed cell foam beyond the first inch for air-sealing & dew-point control is something of a waste in studwalls, especially full-dimension 2x4 studwalls common in 1920s construction due to the higher framing fraction will hit around 25% even in balloon framing (30% or more with doubled stud plate & fireblocking type framing). Assuming you can get a full 3.5" of R8/inch into a full-dimension 2x4 cavity, at a framing fraction of 25% is only ~R11, which is only about a 10% improvement over the ~R10 whole-wall you'd get with full-4" of open cell foam or cellulose at a fraction of the cost. (The HFC blowing agents for closed cell are also likely to have a higher life-cycle greenhouse effect than any amount of energy use it's offsetting over the next century too.) If it's planed standard-dimension 2x4s and 3" of closed cell foam the framing fraction might be as low as 20%, but the whole-wall R would still run about R11, and a full-fill of 3.5" of open cell foam or cellulose would run R9.5, thus the high-R foam still not a huge improvement. You can only reap the full benefit of the high-R when it's outside the sheathing, thermally breaking the framing. But 3" of closed cell foam adds considerable structural strength against hurricane force winds.

Dormers add a lot of framing-fraction too. I suspect this house has 2x6 rafters, which doesn't allow for much attic-R, but it'll be tighter and higher-R if you take an unvented approach, with 2" of closed cell foam (not more, or you risk trapping moisture) against the roof deck with blown fiber (damp sprayed cellulose, if you can) filling the rest of the space between the roof deck and interior gypsum (OSB would also be OK in unfinish areas behind kneewalls, etc.) When it's time to re-roof it's then worth putting 2-4" of rigid foam board above the roof deck with either a vented or unvented nailer deck above that. (If above-the-deck foam is in the cards this time around say so, there are lots of details to get right.)

Do a room-by-room heat load spreadsheet on the upstairs bedrooms- I suspect the heat load of any one room is already well under the output of even the smallest mini-split head, but the combined upper story rooms are probably still over half that. Using an ERV with an exhaust-only registers in the bedrooms and bathrooms, and supplies only in the spaces with mini-split heads also helps balance room temps. This works much better when the whole-wall-R is north of R25 (twice what you'll have), but it's still worth doing. Ventilation supply to those rooms can be via door-cuts/jump-ducts/grilles, etc.

While foaming the band joist was an import first step, insulating basement joist bays is far less effective than insulating the foundation itself (with either 2" of closed cell spray foam or 2-4" of rigid EPS.) This also keeps the basement warmer & drier both winter & summer, reducing mold & mildew hazard on any goods stored down there by a HUGE amount. Insulating between the joists just leaves the joist edges colder in winter, which leads to higher average moisture content, putting them at higher risk of mold/rot. If you use the basement for ANYTHING, even if it's just there to house your hot water heater, it's better to convert the basement into a sealed semi-conditioned space.

In air-tight homes any combustion equipment should be direct-vent/sealed combustion, especially in high-wind areas like the Cape where wind direction & intensity can too easily reverse the flow direction of flues.

Posted By Bob I on 10 Feb 2013 09:06 AM
One benefit is that solar PV panels can be added to supply the "fuel".

How much "fuel" would he get with a PV panel. And, what would it cost per therm?

Posted By BadgerBoilerMN on 11 Feb 2013 11:42 AM

Posted By Bob I on 10 Feb 2013 09:06 AM
One benefit is that solar PV panels can be added to supply the "fuel".

How much "fuel" would he get with a PV panel. And, what would it cost per therm?

At current MA subsidy levels and net-metered against some of the nations highest non-island electricity prices, and (some of the highest gas prices too, since about half of it comes in by LNG ships rather than pipelines), an array of PV convering half the roof on a 1000' cape would likely cover more than half the heating costs, and reduce the annual utility billing to well under that of a condensing-gas heating solution would get you.

It's a chunk o' change up front, and waiting until re-roofing time would be advisable, but even un-subsidised, current grid-tied PV pricing the lifecyle cost per kwh is 1/2-2/3 that of retail-residential rates from NStar or National-Grid.  (IIRC most of the power on the Cape is served by NStar.)  At recent MA power & gas rates the cost of heating with mini-splits on the Cape would cost maybe ~15% more than heating with condensing gas, and if you net-metered out even 1/3 the heating use total with PV it'll be measurably cheaper than heating with gas.

Gas currently holds the largest fraction of the generating capacity in MA and recently power prices have tracked gas prices. But with the existing MA RPS plan renewables will have a much larger fraction in the intermediate term, moderating price volatility by a considerable amount, bringing the average costs of PEAK power down considerably, especially when the Cape Wind offshore project comes online As much as the detractors complain about the higher-than-current-retail contract price for that power, it's still well under the wholesale peak power, and the effect it will have on long term rates will be to suppress electricity price inflation.  (disclaimer: I'm distantly related to the developer of that project, though I was a fan of the project long before I discovered the personal connection.)

"Good idea with PV, I wish but my roof is facing east and west "
two words: Ground Mounted"

That is the longest answer I ever didn't get. Sure you're not a politician? :-).

Another factor I haven't heard yet is the additional gas service monthly charge incurred. You could easily be looking at over a hundred dollars a year just paying for the gas service fee. If you went with a split system and a heat pump water heater, will the operating cost be more than it would be with the gas service plus the service fees? Just something to think about.

I haven't done any load calculations, but I'm sure once it's properly insulated and sealed on the second floor ceiling min R-30+ (not insulating rafter bays) I will be able to heat with 50,000 btu. I'm also gonna add two ceiling fans to circulate air through house regardless. I like the idea of having cold bedrooms anyways. I can do a cast iron primary heat source and back up with splitless ducts
@Stratgery- That is very feasible using a H20, because I have to buy a water heater anyways, and it does offer many different options like radiant tubing, but I need to look at some different options, because I don't want to sacrifice much floor space, and new radiators look $$$. The Rheem 9.5 gpm unit is real slick. http://bit.ly/VPZXb9

@Bob I- two words: cost prohibitive. Not to mention, I have a 1/10 acre lot with narrow 40' direction facing south and obstructions i.e. trees and neighbors. Solar is great at lower latitudes but you've gotta have some space or elevation when you live at 42° North. If solar was $2/watt (installed) it would be worthwhile as redundant system.

Posted By natlseashore on 11 Feb 2013 07:45 PM
I haven't done any load calculations, but I'm sure once it's properly insulated and sealed on the second floor ceiling min R-30+ (not insulating rafter bays) I will be able to heat with 50,000 btu. I'm also gonna add two ceiling fans to circulate air through house regardless. I like the idea of having cold bedrooms anyways. I can do a cast iron primary heat source and back up with splitless ducts
@Stratgery- That is very feasible using a H20, because I have to buy a water heater anyways, and it does offer many different options like radiant tubing, but I need to look at some different options, because I don't want to sacrifice much floor space, and new radiators look $$$. The Rheem 9.5 gpm unit is real slick. http://bit.ly/VPZXb9

@Bob I- two words: cost prohibitive. Not to mention, I have a 1/10 acre lot with narrow 40' direction facing south and obstructions i.e. trees and neighbors. Solar is great at lower latitudes but you've gotta have some space or elevation when you live at 42° North. If solar was $2/watt (installed) it would be worthwhile as redundant system.

Damned-straight!  Do the heat load calcs, seriously! You're probably looking at less than HALF that 50K number, which is definitely in ductless territory, even if it's not always a slam-dunk.  A typical pretty-good 3/4 ton mini-split puts out about 12,000 BTU/hr @ +5F. You may be able to skate by with just two of those (or a 1.5-2 ton 2/3 head multi-split) but no more than three for sure. 

I'm betting it comes in around 15,000 BTU/hr for heating, using any reasonable indoor & outdoor design temps, in which case ANY cast iron boiler solution would be grossly oversized, but a condensing tank water heater combi would run at reasonable efficiency.

A heat load of 50K for a 1000' house would be 50BTU/foot, which might be the case with your house if by "Cape" you were referring to Cape Evans, Antarctica rather than Cape Cod, MA.   

For comparison purposes and sanity checking, I'm living in a circa 1923  2x4 framed 2400' house (+ 1500' of insulated basement that never drops below 65F) in Worcester (design temp about 8-10F colder than yours), and most of the cathedralized ceiling is R19 or less between rafters with the exception of about 300 square feet where it's a bit better, there are KNOWN GAPs in the mostly-cellulose wall insulation, original '20s-vintage double-hung windows + clear (not low-E) storms of dubious tightness (but way better than nothing).

It manages to not lose ground even at -8F outdoor temps even though it's radiation-limited to ~43-44KBTU/hr at the water temps I'm running.  Running the numbers on fuel use (even without subtraction for hot water) the heat load at the 99% design temp of +5F is well under 40K, but still over 30K.

Quick & dirty heat loss calc:

Say that's a 25 x 30' exterior perimeter (750' first floor) with 8' ceilings, 9' between floors, with the upstairs somewhat smaller footprint than downstairs, the typical head-banger 2-story cape.  Figure R10 whole-wall (U-factor= 0.1 BTU/ft per degree F) and a 60F inside/outside delta-T. Your exterior area will be not more than 2 floors worth, but lets call it 18' x 110' of perimeter, or 1980 square feet of wall area, less windows & doors, let's call it 1500', with 480' of U0.30 window.

Wall losses:

1500 x 60F x 0.1= 9000 BTU/hr

Window losses:

480 x 60F x 0.30= 8640 BTU/hr

R30 between joists comes in at about R25 after thermal bridging, or a U-factor of about (1/R25=) 0.04BTU/hr in 750' of attic

750 x 60F x 0.04= 1800 BTU/hr

Add it all up and you're still under 20KBTU/hr.

And that's on a house that's 1500'  not 1000', with whole wall R values somewhat lower than what you're talking with a whopping 32% window to floor ratio for taking in all those great seascape views.

Reality on your real house is going to be quite a bit lower, but run some numbers using your best guesses on surface areas & U-factors, but there's no way a 50KBTU/hr burner would be appropriate unless it comes with it's own buffering thermal mass (like a 50 gallon hot water heater.)

Why are there no smaller condensing gas furnaces appropriate for this situation? Are they not economical to make or have we just moved too fast in terms of getting the heating and cooling load down? I bet there's a lot of people in his situation. It's my situation too really.

Evolution.

We use condensing water heaters with sub-assemblies for space heating. The stored water allows small--micro-loads--to be drawn from the water heater without short-cycling the burner.

Once a house or zone therein gets to a certain load too small for a condensing boiler at low-fire (about 10mbtuh output) one will likely find the domestic hot water peak demand exceeds the design load of the boiler. Thus a condensing water heater with isolation and controls.

Posted By strategery on 13 Feb 2013 01:26 AM
Why are there no smaller condensing gas furnaces appropriate for this situation? Are they not economical to make or have we just moved too fast in terms of getting the heating and cooling load down? I bet there's a lot of people in his situation. It's my situation too really.

Most furnaces sold are replacement units not for newer-tighter buildings, and even on new construction oversizing is the norm except where prohibited by code (eg California Title 24.)  HVAC contractors rarely down size from the original equipment, even though the original was 2x oversized for the original house, and after the windows, air sealing, and insulation have been upgraded it's more than 3x oversized. There is very little upfront cost difference even when grossly oversizing hot air furnaces, and very little impact on efficiency too, so they just don't bother.  Tract developers often pick a model and use the same one  for a whole development, even if it's 2x oversized even for the lossiest house, and 4x oversized for the smallest/tightest.

But comfort suffers a bit, unless you go with a multi-stage or continuously-variable burners & air handlers.

Ductless solutions are nice in that they're at the lower end of the output scale and they modulate with load, with 3:1 or better turn-down ratios. 

There are some tiny European mod-cons boilers out there too, but the bottom of the selection from most US vendors is ~50KBTU/hr max, with a ~4:1 turn-down.  Even if the design heat load of a tight 1000' house is above the 12-13K output of a 50K mod-con, the average load will be well under that, and it's not a great fit. (A mod-con sized such that never modulates is just silly.)

Dana1, Thanks for the load calculations, they are very comparable for my house. I was WAY outta line with 50k, but i'm so used to seeing it sourced, it's like second nature. This opens up all new possibilities. I will fine tune the numbers and i'm closer to a solution. I will try to post pics, but 100k limit is tough to size

Putting your higher-res pics on a picture hosting site then posting links to it here gets around file size (but not burner size :-) ) issues.