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Discussion Starter · #1 · (Edited)
A modest 3 bed and 2 bath home will be built in a cold climate with a winter design temp of -15 F.

As in many houses today, the common spaces are one large flowing series of volumes, and the largest of them is the great room with a big tall vaulted ceiling, averaging 17 feet in height. Flanking that space is a tall wall of windows with a frenchdoor exit, and this bunch of glass all faces south.

The place will be occupied typically in the July through October timeframe each year, with occasional week-long visits in the snowy winter, for ski vacations.

The intention is to build and insulate it well, and focus on best practices for sealing and ventilation, and heat it with a small mod-con boiler, LP-fired, supplying 160 F. water (max) to panel radiators throughout.

The system will be in the 4'-deep crawlspace foundation under the main floor, and that will be either built with ICF (R-25) blocks, or conventional poured concrete, and insulated and sealed very well. No ventilation. We estimate that the presence of the boiler and system in that space will condition it so that there is essentially no heat loss into it from the living spaces above.

I used Slant-Fin's Hydronic Explorer 2 package to calculate the room-by-room heat loss, and arrived at a total a little over 37,000 Btu/h at the design temp, with over half that amount happening in the large common greatroom.

The smallest mod-con I can find, using web searches, is the Knight Lochinvar wall-hung with a net I=B=R output of 39K Btu/h, and a 5:1 turndown ratio.

What might you recommend?
 

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Weil McLain Ultra 80.
Has 5 to 1 turn down. Giving you 16,000 input at lowest modulation.

Will be large enough to both heat home and your domestic hot water.

Provides quick recovery for those times you go there in the winter. Includes outdoor reset as standard.
If it detects its temp getting too low in winter. It will run the circ to protect it and the piping from freezing as best it can.

Can use antifreeze in it(must be made for aluminum).

Presume you are installing a system to notify you or someone if the house temp drops below a safe level in the winter(should be done no matter what boiler you use).

Size your panels to handle the heat load at a water temp of 140°F or less.
 

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Discussion Starter · #3 ·
Got a W-M Ultra 80 running

In a house I built on contract for a client, finished three winters ago. Runs the basement in-floor, plus the staple-up plus some Runtal panels for the 2200 sf main level of a two story house. Seems to be working just fine.

But this little house needs less than 39K at full design load.

Sizing panel rads for 140 means I need to line just about every available foot of exterior wall run in that greatroom and foyer with 16" high 22G double-convector types.

I know I'll short-cycle less the lower the water temp, but was thinking that 160 would be OK. Not?

The W-M Ultra 80 would seem like overkill for this size heating need. I know nothing about the Knight, but thought that at 45K I=B=R output and with a 5:1 turndown, having that nice little 9K output at lowest mod might be right for this small house.

I had planned for the boiler to do the 40g indirect for DHW.

What do you think?
 

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The Knight will be small for a 40 gallon indirect and heating.

When you go there in the winter, and turn the indirect/back up. You won't have any heat for more then ½ and hour.

The Ultra 80 will start heating in about 20 minutes.

With both the Ultra and Knight. Water temps of 160 for heating reduces it efficiency. Little to no condensing.

What GPM are you designing your baseboard for?
 

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Discussion Starter · #5 ·
I'm not qualified to design the system,

and am just designing the house, but I want to know as much as I can about all this.

I have done heat loss analyses for each house I've ever planned or built, though, and my figures have always closely tracked whoever gets the job for designing the package. My need to know boiler size relates to placement of the system in mechanical space, and my need to know heat loss relates to room design to allow for panel radiators. Panels with TRVs is the preferred method for this project.

Regardless of boiler size and make, the heat loss is what it is, and the radiator arrangement for the common space of the house is as shown below. All are Myson 22G double convector units, and all are figured at a supply temp of 140 F. That is per your recommendation, and thanks for that. Callouts show Btu/h and size of each.

The owners will have a couple things going for them if arriving in cold weather. One is that they hope to have a system with telephone control so that by dialing up the day before, they can get some heat going. I'm not really sure that can be accomplished with TRVs, but we intend to look into it.

The other thing is that the wood stove shown will be used for a quick warmup when necessary, and the stoves in consideration all have outputs that exceed the total heat loss of the entire house at -15 F.
 

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Will the wood stove have its own direct combustion air intake?

Nice layout.
At the dining room table. Right side has convectors at windows. Bottom toward use in pic has them at walls? Instead of window. Could give someone a cold draft feeling on their neck/back when seated there.

2 nice things about designing for 140° water temp. Gets good use of mod/com boilers efficiency. And, if the owners ever decide they now need it warmer then originally planed for(happens with some older people, or when they get older). if the boiler is big enough. they can set the boiler/outdoor reset for 150. And get the temp higher. Instead of just wishing it was warmer.
 

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Discussion Starter · #7 ·
That is a sliding glass door at the bottom of the picture, thus no ability to get an emitter under it.

In really cold conditions, they can just pull that table a little ways away from that cold door, but the pic shows another glass door on the R side of the room.

Principal use for this place is as a summer and early fall retreat, and during all that use, these doors will be open to the outside most of the time. It is hard in this small space to strike a balance between warm weather comfort (lots of windows and open doors) and winter warmth.

Yes, the stove will be equipped with a sealed outdoor air intake.

As regards the boiler and its capacity, I would rather be a little undersized than oversized. These designs for low temp, target really a few days or hours of each winter, with the majority of the time seeing far less heat loss. I would like to avoid short cycling, and that wood stove can augment things really well, if need be.

Furthermore, the figures we use in the heatloss calcs are pretty conservative, when you consider today's building practices and window and door products. This place will get spray urethane at its rims and roof edges under the vent chutes. The windows will have u-values of around 0.3, even though we use 0.36 in the calcs. Foam sealant will be used everywhere, aggressively, to see that air infiltration is reduced to as close to zero as possible. Etc., etc.
 

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Duh. Sliding glass door. Yeah, not a good place to put a convector. LOL

Sounds pretty air tight. So are you also specing an HRV to comply with ASHRAE fresh air standards?

Or just leaving it as is. Since they currently plan to have the windows open much of the time?

Tight(actually tight)construction can have high humidity in the winter. From the people, showers, cooking, etc.
 

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Discussion Starter · #9 ·
A guy is owner/building a nice house from plans I did, and its HVAC is unusual for our locale. His is a forced air system, open-loop well-sourced geothermal, unit by WFI of Fort Wayne, IN. Small house with a huge array of windows facing south, all windows in house triple-pane low-e coated xenon-gasfill, frames of pultruded fiberglass, units all by ThermoTech windows of Ottawa, ON. Blower door tested to find every last crack and hole, after working hard first to seal everything. R-70 cellulose fill in under cold roof, foamed wall cavities, thermally broken studs used (try to find them!), Fantech HRV into which are piped all three bathroom vents, and the HRV is feeding fresh into the return of the waterfurnace as required.

With the place all buttoned up and tight, mechanicals all done, but still under construction (drywall work to begin shortly), the place was totally comfy on our -25 morning recently, even if near any of the floor-to-ceiling glass bays. Amazing.

This little vacation home will never ever be lived in year round, and will have plenty of time each year to dry out. We'll not use an HRV, but of course will vent the baths. Thanks for your help and advice.
 

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On another forum I'm on.
One member there has a 4,000 sq ft house. Cooled by a 2 ton A/C.

So many people don't realize what really tight construction can do for them when it comes to energy savings.

My own place has an over sized oil furnace, 140,000 BTU input(I'm too lazy to tear it out, and put another one in it). :whistling

With out doing anymore tightening to the house(1650 sq ft) I only need a rounded up 36,000 BTUs output.

Once I tighten it. I'll only need 22,400 BTUs output.


good luck, and take care.
 
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