Heat Loss question

RoosterBoy

I just finished a heat loss calc using HVAC-Calc Res 4.0 and I have a question about the results and boiler selection. This is for my own home.

My heat loss is 71,000 for 2700sf in Boston area using a 0 degree outdoor, 70 degree indoor. The boiler I want to use is the gas fired Buderus G124x/25 with a 103,000input, 85,500output and 75,000IBR. Outdoor reset. I have designed exactly 75,000btu of mostly fin-tube radiation +2 panel radiators using the heat loss calc to size individual rooms. Have I left enough safety factor into the calc by designing right up to the IBR? (1.15 factor of net output).

Lets assume I have evaluated my envelope fairly accurately for a minute. Would you recommend not designing right up to the recommended installed radition? I'm not the type that needs perfect 70 degree indoor temps on the 99th percentile coldest day. I'm energy conscious and want to go with a smaller boiler vs. over sizing but, of course I don't want to undersize.

Thanks for your comments.

Ed

Al Letellier

heat loss calc.

According to the information you give, and assuming the calcs are correct, you've made the proper choice of boiler, in my book. It will give you some added punch on those few and far between colder days (haven't we had some of those this year???). However, what about your hot water demands. This boiler coupled with a 40 gallon indirect should provide sufficient hot water for a normal family without a large tub. If you are planning a whirlpool or have a heavy hot water depand (lots of showers eetc.) You made need a larger boiler to produce the recovery rate you need.

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RoosterBoy

Thanks.

I just installed a Bradford White 75gal DHW last year before I knew I was going to replace the entire heating system. Should last a while but your point is well taken. I may like to add indirect down the road and I'm not sure 40gal is enough with 2 full baths (1 with jaccuzzi) and 2 half baths. But, like I said, we are very interested in conservation of energy so I'm reluctant to go to the G124x/32 (110,000 output) for something I MAY do way down the road. Plus I thought the Buderus will interupt the heating circuits to produce HW anyway so shouldn't the smaller boiler be ok?

I'm having a heat loss done by the installer as well so we'll see how mine compares to his. I did get into a good amount of detail in the calcs BUT any measurement is only as accurate as the tool you use. I'm not sure how much faith to put in the software. Sounds like most users here think it does a decent job.

Ted_9

I agree with Al.

I use that program often. What did you put for the construction under infultration?

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Bob Morrison_3

Looks good

Assuming the stated loads, the choice of boiler looks fine. A smaller output would not improve operating efficiency. What did you use for an infiltration rate for your load calcs?

The amount of heat emitter seems adequate, but what entering temperature did you assume? Additional emitter could provide better comfort by shortening the pickup time and allowing a lower entering hot water supply temperature during steady state periods. But, that adds cost and you may not have the installation space.

I have a G124x/18 DI with the indirect DHW and Logomatic controller. It has operated well (at specified efficiency) for about 4800 hours (the Logo tracks operating hours) over four years.

Bob Morrison

RoosterBoy

I used .8 air changes/hr-here's why:

I started with the ave. setting (.7 air changes/hr) which is loose, no vapor barrior. I'm pretty initimate with my envelope as I've spent the last year sealing it up best I can. 6" Icynine in attic, 8" Icynine in floor over garage. Harvey True Channel storms and storm doors with fairly tight sashes on double hungs. The stud cavities are filled with rag wool that is in pretty good shape-still full in all the cavities I've opened. I re-sided the top half of the house so that has tyvek. The problem with HVAC-Calc is its wall construction value. You get R11 or nothing. I think my walls are somewhere in between so I used .8 infiltration to compensate.

One room (master bed) has 14 windows in it overlooking a great view. That room alone was 18,000. So much for conservation of energy, huh...?

RoosterBoy

Bob, hows the noise factor on the draft inducer? I'm considering doing the GA124 sealed, internal inducer which I here is very quiet. Is the DI on the outside of the G124 hood quiet? How about at the vent outlet? I would consider it over the GA124 if it was reasonably quiet.

We had originally installed the DHW with a power venter and hated the noise. Its a real quiet neighborhood but the houses are tight. The sound echoed off our neighbors wall. We ended up ripping it out and keeping a chimney taht wasn't really in the way to begin with. I could go either way on the boiler.

RoosterBoy

Forgot to answer your question. I used 180 supply temps. Actually, I can afford to do lower temps. I have the space. I may also swap in some panel radiation in place of baseboard. I assumed 600btu/ft for fin-tube. Is that to aggressive?

So increasing area of radiation and lowering temps will improve efficiency correct? I'm also going to install the logamatic.

Bob Morrison_3

the induced draft fan is noisy

I find the induced draft fan noisy - you need to markedly raise your voice to be heard if standing next to it. The vent discharge outdoors is not noisy. I have not yet seen (nor heard) a GA124, so I can't compare.

I live in Sudbury, MA and you're more than welcome to visit and check the system out. Email me at robert.l.morrison@comcast.net, if you're interested.

Bob

RoosterBoy

Thanks Bob. I'm in Arlington and have family in Dover. I'll contact you.

Bob Morrison_3

efficiency increase is slight; 600 BTUh/LF may be aggressive

In theory, lower supply water temperature will reduce standby losses from the boiler and distribution piping. Often, though, for homes, most of the losses are to heated areas anyway. And, if you install the Logomatic, the supply temperature will be reset, so it's only the design day entering supply water temperature that's really at issue, if the losses contribute to the building's heat. (BTW, if your piping is in an unheated area, then it needs to be insulated to conform to MA. energy code.)

The 600 BTUh/LF: which finned tube are you considering? I'm in the process of installing DiaNorm panel radiators, which, if they perform as well as they look, should be fine. I selected them at 160 F entering, which derated them to about 65% of their output at 180 F. I selected the next size up, also, when between sizes.

Bob

RoosterBoy

Finned tube

I have not done much research on baseboard manuf. My installer mentioned a brand (not Slant-Fin) but I can't recall the name. I would love to do the whole place in panels with TRV's but from the limited amount of pricing I've seen on Buderus panels they are about 3-4 times the cost. Myson seems to be affordable but not sure of the quality. I can afford a few though. Any problems with mixing panels and baseboard on the same zone?

Bob-did you take any low return temp protection measures other than relying on the Logamatic pump logic? Seems Buderus approves of a 106 degree boiler temp before the Logamatic shuts down the circs. Does that 106 temp give you a wide enough outdoor reset range? I'm only doing hi-temp circuits but with the reset temps being what they are in the shoulder seasons, are there additional measures worth considering (primary/secondary, mixing, etc)?

Thanks

Ted_9

thepassenger, look into The DiaNorm panels, they are the same as the Buderus. I use both brands. There may be a price differance for you.

The GA124 is my favorite cast iron gas boiler and its the quietest.

Make sure your installer is familiar with the products being proposed.

Also note: Sometimes the heatloss of a house is less than the domestic hot water load. Thats why you may need a bigger boiler.

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Bob Morrison_3

return water low limit control

I did not include any adddtional protection. I have not found the lower limit to be a problem.
I will eventually install floor heating on a lower level area, but, for the most part, it's a high temperature emitter system.
If I were to start over, I would consider primary/secondary, but only on account of the floor heating. With high temperature circuits only, the costs of primary/secondary outweigh the benefits. A relay board, such as the Taco SR50x series with individual zone pumps (each pumping through the boiler) is a simple and good approach for finned tube.

Check out heatlines.com for information about DiaNorm. You might want to call Pieter, the distributor, though ... it looks like the website is having some problems.

Bob

thepassenger

Great Help Everyone

Thanks you guys. I'll check out DiaNorm. I'm glad to hear the boiler won't need additional protection. I like to keep things simple.

I keep leaning towards the GA124 but after the DHW noise issue my wife is going to be the tough sell on draft inducing. Any place that we could listen to one that is installed? Then again, I like the shape of the G124x better...

Ted_9

I think you misunderstand. The GA124 IS the quiet one. If you use the G124x and buy the inducer seperatly, it is a bit noisey compared to the GA124.

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thepassenger

GA124

I certainly have come to understand that the GA124 is the quiet one (due to its blower being inside the jacket). Its my wife that I will need to convince. She has categorically stated she will not buy anything with a draft inducer of any kind unless she can hear it first. It was tough enough swallowing the 1st DHW heater (FW Webb said we couldn't just take the stupid inducer off). A boiler is a much bigger investment...

Ted, you guys are on the south shore right? Do you do work in my area? I'm still considering installers if you would be interested. May be to far though, its up to you. I've read many of your posts here. Thanks.

Ted_9

Yes, give us a call and we'll make an appointment. Call me @ 508-991-3298.

Ted

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