What about a heat load calculator here at HH?

hot_rod

I think one of the most common responses here is "what's the heat load"? Would it be useful to have a form available for folks to at least see what is involved in developing a load calc?

Granted blower doors and infrared scans may add to the accuracy, at least it gives homeowners a homework assignment and shows where the biggest loads are in their building.

The Pikes Peak Building dept has a simple hand form on their site.

https://www.pprbd.org/plancheck/Heat_Loss_Table2011.pdf

RobG

Or (with permission) do a tools section with links to Slantfin, Uponor ADS, PPBD et al... and people can choose what works best for them?

JStar

How about a way to pay something like $XX and one of us can do the heat loss for real.

Paul48

That would be better for Holohan family. If you develop one and put it here, you have to listen to the crap, when folks do it wrong . There are enough, already out there, but having links to them here is a great idea.

hot_rod

links would be an option. I'd like to see a generic method like the old IBR or Hydronics Institute forms.

I think all would be well served if the owner had skin in the game and understood how and where the number comes from. And why it is so important. I'd rather they get the info here than some of the online designs with a simple multiplier, or climate zone factor.

Certainly the Find a Contractor button is still available. Not everyone is within reach of those listed, however.

Jason_13

I have been doing heat losses online at comfort-calc for about 9 years and never had one issue, knock on wood. they fill out the forms and I contact them with questions and to verify some items.
The only complaints I get from the homeowners is sometimes they cannot find anyone to put that small of a boiler in.

Chester

Sorry for the long post....

As a homeowner who just went through the process I had a chance to compare several methods including the Slantfin software, a professional Manual J analysis, and my own calculation based on actual fuel use vs. heating degree days.

The fuel use/HDD calc was virtually identical to the Manual J (about 30,000 BTU/hr). The Slantfin result was about 20% higher. I decided to stick with the Manual J since I wasn't completely confident in the assumptions I used in the Slantfin model.

I'm feeding around 90,000 Btu of cast iron radiator capacity (at 180F). So I replaced my 140,000 existing unit with a 55,000 modcon and I'll be able to dial in the ODR curve at around 130F on a design day. Pretty sure I'll hit AFUE or better for most of the heating season. I feel sorry for all the consumers who buy oversized "95% efficiency" boilers that will never come close to AFUE.

Related to Jason's comment above, out of the contractors I spoke with most wanted to install a 110. One even said he wouldn't take the 'legal liability' for installing anything less than 80,000 -- even if the invoice said customer-specified equipment.

So, if your customers can provide actual heating season fuel use (a couple month's worth is probably sufficient) it's easy enough to compare that with published heating-degree data for the same period and get a pretty accurate heat loss number. The basic formula is:

Implied Heat Loss (BTU/hr) = (Heating Degrees) X (BTU/degree-hour)

In case it's helpful, here's the calc based on my actual data for a reasonably well-insulated 1400 sq ft cape in Maine:

I used 534 gallons propane 12/6/14 through 3/23/15 = 48,861,000 BTU (rounded down to 41,531,850 actual heating value assuming 85% boiler efficiency)

Base 60 Heating Degree Days during same period = 3,855, or 450 BTU per degree-hour (I used Base 60 instead of 65 to be conservative.)

ASHRAE 99% design temp for Portland ME = +2F

Design day heat loss = 30,600 BTU/hr

I also looked at my average fuel use for Jan/Feb 2015 (46.3 HDD) which gave me 20,835 BTU/hr. So at least I was able to get a small enough boiler that can meet my design day, modulate well below a winter average, while still giving me decent DHW recovery via my indirect. I'm almost looking forward to winter to see how it works.

Ironman

I like the idea of a simple form to get in the ballpark quickly. Grundfos has one in their handbook and I used to use a one page one back 30+ years ago that did cooling too. I don't know if I could find it now, but I'll search. Maybe Dan could get Grundfos' permission to use theirs here?

For those wanting more detailed and tighter results, a link to Slant/Fin's or others could be posted.

JStar

The Slan/Fin app doesn't account for the cardinal direction of windows for sun exposure. That's why the numbers can be off by +/- 20%.

oak

My original heat loss calcs were pretty accurate; modifed IBR approach. I used electric heaters for one winter after we insulated during construction and now the finished system is hydronics with a 110 condensing, gas fired, boiler. Both energy bills reflect the original calculations within a few BTU's/hr/sq ft. We are very airtight and very well insulated.

What was a problem was figuring out the hot water in an integrated system. I have an indirect fire, tank in tank boiler, so the classic heat calc's form needs to have a section to account for and guide DHW demand. Also, our well supplies 10 - 15 * cooler water than the town water. That needs to be considered for total BTU's on the DHW side.

Yes some basic proven on-line forms and templates would be great. System design analysis is one objective; energy use and cost-benefit is the other. A formula for comparing design options and anticipated performance would also help put contractor and owner on the same page.

Sorry if I digress the topic.

hot_rod

oak said:

My original heat loss calcs were pretty accurate; modifed IBR approach. I used electric heaters for one winter after we insulated during construction and now the finished system is hydronics with a 110 condensing, gas fired, boiler. Both energy bills reflect the original calculations within a few BTU's/hr/sq ft. We are very airtight and very well insulated.

What was a problem was figuring out the hot water in an integrated system. I have an indirect fire, tank in tank boiler, so the classic heat calc's form needs to have a section to account for and guide DHW demand. Also, our well supplies 10 - 15 * cooler water than the town water. That needs to be considered for total BTU's on the DHW side.

Yes some basic proven on-line forms and templates would be great. System design analysis is one objective; energy use and cost-benefit is the other. A formula for comparing design options and anticipated performance would also help put contractor and owner on the same page.

Sorry if I digress the topic.


Good point, in modern, well insulated homes it is possible to have a larger DHW load. Now what?

Suppose a 1500 sq ft home has a 10 btu/ ft load. How would a boiler sized for that load cover reasonable DHW. It could have a DHW mode where the output doubles for DHW, but that same HX would not be ideal for the 15K at design and lower load.

Personally 35K or more is a realistic number for DHW, as far as what the consumer expects for recovery. That is about what a typical 40- 50 gallon gas fired WH burner is.

This is also one of the weak points to heat pump water heaters is the very slow recovery.

a9876

Hot rod, sorry my question off topic. In one of earlier discussions on radiant heat, which is closed, you mentioned that your favorite is hardwood over Roth panel. Is there soft feel to the floor if it is over foam Roth panel? Did you have to put something between panel and floor to make it sterdier? We are considering Roth for slab application. What are the pros and cons? How it would need to be installed if we plan for engeneered wood floor but would like to keep an option for hard wood? Are you in NJ?

hot_rod

Yeah, the foam based Roth system does have a bit of give to it.
The large job I did had about 8000 square feet of walnut T&G flooring. The owner, a doctor pulled the walnut from his farm in Arkansas and milled it all on site. The walls also had some walnut wainscot, incredible home, all ICF construction from the ground to the roof.

The wood was installed directly on the Roth Panel. The beauty of that was the installer could see every tube and bend. Although they still hit a few tubes. The system was up and running as the floor went down. It took about 3 months!

I glued and stapled every Roth panel down, used a special foam adhesive and a wide crown staple, like roofer use on wood shingles. A cordless electric caulk gun helps, it took a truckload of adhesive tubes.

The 3/4 wood floor matched up perfectly with cement wonder board and tile at all the bathrooms, no tapered transitions were needed in the entire home.

We found an extra long cleat. A cleat is this serrated T headed fastener used on hardwood. A pneumatic tool drives the blunt end down through the tongue without splitting it.
Really should not use nails on hardwood, according to the Oak Flooring Association.

We adjusted the angle of the gun up so the cleat was at a steeper angle. It reached through the 1/2" foam and into the Advantech subfloor just enough. The cleat only needs to go into the subfloor not completely through. So the subfloor held the flooring down, not the foam panel

This was 10 years ago, check with Roth or whoever you chose for their installation suggestions. I see the contractor from time to time, he and the owners are happy with the flooring. I contribute that to the very low operating temperature due to the continous aluminum surface, and probably the humid Missouri climate.

Engineered flooring could either "float" or be glued down to the Roth. Check with the flooring manufacturer.

www.launstein.com were my go to guys for hardwood over radiant questions. They have tested all sorts of woods and radiant installation methods.

Sadly Don Launstein passed this summer. He was a fun fellow, a longtime RPA supporter, RIP.

Robert O'Brien

Chester said:

Sorry for the long post....

As a homeowner who just went through the process I had a chance to compare several methods including the Slantfin software, a professional Manual J analysis, and my own calculation based on actual fuel use vs. heating degree days.

The fuel use/HDD calc was virtually identical to the Manual J (about 30,000 BTU/hr). The Slantfin result was about 20% higher. I decided to stick with the Manual J since I wasn't completely confident in the assumptions I used in the Slantfin model.

I'm feeding around 90,000 Btu of cast iron radiator capacity (at 180F). So I replaced my 140,000 existing unit with a 55,000 modcon and I'll be able to dial in the ODR curve at around 130F on a design day. Pretty sure I'll hit AFUE or better for most of the heating season. I feel sorry for all the consumers who buy oversized "95% efficiency" boilers that will never come close to AFUE.

Related to Jason's comment above, out of the contractors I spoke with most wanted to install a 110. One even said he wouldn't take the 'legal liability' for installing anything less than 80,000 -- even if the invoice said customer-specified equipment.

So, if your customers can provide actual heating season fuel use (a couple month's worth is probably sufficient) it's easy enough to compare that with published heating-degree data for the same period and get a pretty accurate heat loss number. The basic formula is:

Implied Heat Loss (BTU/hr) = (Heating Degrees) X (BTU/degree-hour)

In case it's helpful, here's the calc based on my actual data for a reasonably well-insulated 1400 sq ft cape in Maine:

I used 534 gallons propane 12/6/14 through 3/23/15 = 48,861,000 BTU (rounded down to 41,531,850 actual heating value assuming 85% boiler efficiency)

Base 60 Heating Degree Days during same period = 3,855, or 450 BTU per degree-hour (I used Base 60 instead of 65 to be conservative.)

ASHRAE 99% design temp for Portland ME = +2F

Design day heat loss = 30,600 BTU/hr

I also looked at my average fuel use for Jan/Feb 2015 (46.3 HDD) which gave me 20,835 BTU/hr. So at least I was able to get a small enough boiler that can meet my design day, modulate well below a winter average, while still giving me decent DHW recovery via my indirect. I'm almost looking forward to winter to see how it works.

Oh Boy!!

Chester

???

I definitely took my DHW needs into consideration. I've seen folks here and on other forums engage in passionate debate whether or not boilers should be upsized to accommodate DWH load and my judgment was that my Greenstar 57 had plenty of headroom. The 'design condition' test for my needs is whether I can take a hot bath in my relatively large tub in the middle of winter and then have a 'reasonable' recovery rate. I run my TT Smart30 indirect at 145F and mix it down to 120F and it's never taken longer than 10 minutes or so to recover even after I've completely hammered it. And I can run the tank up to 158F if I need more capacity. Can I take my bath while we're running the dishwasher and doing a hot load of laundry? Probably not. But that's my choice.

I'm hitting the indirect with 180F water from the boiler, so I'm not condensing while it's charging. But I figure that's an easy trade off considering the heating season efficiency I'll get. By way of contrast, the contractor I spoke with who was most concerned with pick up load and DHW capacity wanted to install a TT Solo 110, which would barely modulate down to my design day need. If I wanted to go that route there wouldn't have been any point in investing in a modcon.

Obviously, DHW design needs to take into consideration a homeowner's personal requirements and preferences. But even if I needed more hot water I think I'd go with less boiler and more tank based on everything I've learned from you guys.

hot_rod

good points on DHW. That elevated temperature in a DHW tank can offset some BTU requirement, especially for a tub dump load.

Lochinvar U offers this very handy calculator, at their website, along with a bunch of other handy tools.

Chester

Correct. But I did it that way on purpose to err on the conservative side. I didn't net out anything for cooking and hot water, which means my calculated 30,000 Btu/hr heat load is probably the upper end of the range.

My "real" number is probably closer to 25,000, but so what? Even if it was 20,000 it wouldn't have changed my boiler sizing decision.

I learned about this method on one of the other forums and all I'm offering is the observation that it produced a result that was within 1,000 Btu/hr of what a professional Manual J came up with. If I had to do it over again I could probably do it in 10 minutes now that I understand the math. And it's not as daunting to me as the document the OP posted or having to wade through the Slant Fin software with all the measurements and assumptions you have to make.

I'm not a spreadsheet person but if I was I'd volunteer to construct a simple model with all the math built in and that links you to heating degree data, how to find out the EDR of your radiation, etc.

Harvey Ramer

The Guberment estimates that DHW consumes 30% of the energy used in an average residence. That includes all energy, lighting, heating, cooling, ect.

Chester

Sorry, I forgot some people just come here to argue.

jonny88

where is the argument

a9876

Thank you, hot rod, for taking time to answer. This is very helpful.

Chester

Harvey Ramer said:

The Guberment estimates that DHW consumes 30% of the energy used in an average residence. That includes all energy, lighting, heating, cooling, ect.

That certainly makes sense, but I assume it's a national average? I'm wondering if the percentage of fuel used for DHW just during the heating season in a cold climate might be smaller, especially for a household like ours that has relatively low HW demand. I thought I read somewhere else that it could be as low as 10% depending on particular household usage.

hot_rod

I agree that 30% may be high. We used to estimate 20 gallons per person per day in the old solar calc.

I'll bet with low flow fixtures, 20 gallons for the first, maybe 10 gallons per additional people, might be more realistic.

I lived in Phoenix one summer, one of the hottest on record. You could shower by just running the cold water!

The temperature rise must factor into DHW costs.

Sal Santamaura

hot rod said:

...I lived in Phoenix one summer, one of the hottest on record. You could shower by just running the cold water!...

After a few "polar vortex" winters in the northeast, my wife has become reluctant to build a retirement house on our New Hampshire property. Last week, revisiting an alternative I'd previously rejected, we spent some time at a 55+ community in Vail, Arizona, a Tucson suburb.

Being a hobbyist photographer of the Luddite variety, something I always check is "cold" tap water temperature to see how compatible it might be with my darkroom activities. After letting it run for a while to displace water cooled by having sat in the slab (under air conditioned space), Vail Water Company's delivered product stabilized at 91 degrees F. Probably 8-10 degrees cooler than Phoenix's, but still plenty comfortable for a shower.

njtommy

I think it would be a good idea and with the right information and guide lines you could really dial in a great program. Also you would be able to show people the difference in insulating floors and cealing better.