Manual J Provided by Dandelion Air
aaron55
| Posted in General Questions on
Is the manual J I get from Dandelion a good approximation of my heating and cooling load? They have all of my window and door info, size of my house, and they asked me about insulation and such. I also had a blower door done several years ago, which might be off some but it is probably close as not a ton has changed in my house since then.
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In theory, a Manual J is a Manual J, everyone should be following the same procedure. Where that theory falls apart is that the process leaves a lot of room for subjectivity when it comes to assumptions. Residential contractors are notorious for putting their thumb on the scale to oversize equipment, because they know if it ends up undersized they'll be called back to replace it, whereas if it's oversized it will work, just not optimally.
I have no knowledge of where Dandelion comes down or even if there's any consistency across their employees.
I thought they sound familiar. If I’m not mistaken, I saw a clip where they did a project with This Old House or Ross Threthewey.
It's a Google spinoff.
Is it usual practice to design for 72° heating and cooling indoor temperatures? I thought 68 and 78° were more standard.
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
I'd use your own fuel use before a manual J if you're just swapping equipment as your fuel use is what actually happened. If they're good at manual Js, they should be about the same. If they're not checking against actual fuel use, they're just churning out the same mistake.
Generally, not easy to make Geothermal pencil out. You're at a high latitude, which is in geothermal's favor, but you'll need more than just a cold winter.
My fuel use calculations are complicated in that I have been using my wood stove so much. Last year I only used about 20,000 btu/hr with my natural gas furnace. I calculated that I probably used around 20,000 btu/hr of wood as well. So my heat load was 40k btu/hr, but that is for kind of a weird situation where when the furnace is on, my house is only at 65F and then it drops to 58F most of the time. So, my avg temp in my house is around 60F with the gas furnace. Then, I add in the 20k btu/hr average with my wood stove in my living room in the evenings and on weekends. I feel like 40k btu/hr might not be realistic as a usage estimate since I'm super heating the space I use most with the wood stove.
The heating infiltration load is 20k compared to 24k for walls and 9k for glazing! Can you confirm if their input match with your blower door test. If this is correct, would it better to hire some too better air-seal the house (GBA has fantastic article on blower door driven air sealing, https://www.greenbuildingadvisor.com/article/blower-door-directed-air-sealing-2)
Two more cents:
I would also do a room-by-room manual J.
Take shade and window overhangs, etc. details into consideration.
Rajib
So this was what I was talking about when I mentioned putting a thumb on the scale. Often the Manual J software just has the user put in an estimate for leakiness. Putting in a high estimate is a way of goosing the number upwards.
I'd agree with Paul that actual fuel usage is going to give a better estimate than a Manual J.
I had a blower door test done probably 10 years ago and it was 2650 CFM50. However, I can't remember if that was with the attic open or closed. The attic has a lot of leaks I think. I think it was with the attic closed. Anyway, I'm having another blower door test done tomorrow to see how it's changed in the last 10 yrs with minor changes I've made to the house.
Thanks for this. It's very useful. I assume the 20k for infiltration is how the software converts my 2650 blower door test into heat loss, right? That was a measured number from a blower door test several years ago. I know I have a lot I can do to tighten up my house. I'm having another blower door done tomorrow and then I'm going to start working on some of my leakage.
OK, I'll have someone else do a room by room manual J as well. I assume they can just modify it once it is done to account for any changes I make regarding air leakage or insulation. Thanks!
I hadn’t heard of Dandelion Air, so thought I would share this link for anyone else who is wondering about them.
I’m sorry! I assumed everyone knew about Dandelion! It turns out they are mostly NE and very heavy in NYS.
You are right, Aaron. I am embarrassed not to be familiar with them but they just haven't come up in my circle. I thought of this thread when I saw this article: Residential geothermal company Dandelion, fresh off local acquisition, eyes ambitious growth in CT.
Dandelion's niche is replacing furnaces with ground source heat pumps. Since the ductwork is already in place, it should result in $ savings. They started in upstate NY, but may have started branching out. Their marketing is big on how they developed some sort of improvement in drilling rigs that allow quicker, less messy bore holes.
A friend got an estimate to do his house and was dismayed at the cost, even there NY incentives and federal tax credit.
I got a quote for a 6T unit. It was $23k after rebates and federal tax incentive. I haven't gotten an ASHP quote yet, but that seems reasonable to me given how much things cost these days, especially in NYS.
The main thing that disappoints me is that it is only a two-stage compresssor, so it is either going at 72k btu or ~49k btu or off, right? My total cooling load design is likely no more than around 30k btu, so I wonder if it would wear the compressor prematurely.
I thought maybe I'd get better results with either a variable compressor air handler or just change over to mini splits and leave my old ducts behind, which are likely undersized and don't include a return on the second floor anyway. To redo my ducting "the right way" would cost $16k, which seems like a bad investment for me if I can live with the maintenance of mini splits.
$23k (!!!) after incentives for a two-stage is why geothermal has a negligible market share, even in locations with high electricity costs. The cost difference between Ground source and air-source is more effectively spent on solar/insulation/air-sealing/other improvements.
I guess I was expecting an air source setup of that size to be in the high teens at least. I need to get some quotes to see what it would be.
Kind of new to this but it appears that they used 12A wall system in the analysis.
From what I've seen 12A is a non insulated 2x4 wall..is this what you have?
yessir!