Snowmelt questions... Just in time for spring.

mike99

Our driveway is needing to be replaced and is a 21% grade for about 100', combined with the fact that I'm next to a ski resort and it's become a priority to heat the thing. I've attached a plan and it's popped a few questions into my mind.

-Is 40gpm really normal? Referencing Chris Decker's YouTube Channel he's accomplishing about half of my square footage with 8gpm.
-The proposed boiler is $18k. Chris suggests he's heard of people using water heaters successfully for 10 years that are only $1500 a piece.
-At a 21% grade, one radiant designer insisted that the threat of the slab sliding if placed on insulation is too high. And that I would just need to live with the lack of efficiency.
-Would it be possible to heat tire tracks as a separate zone so that I always have a safe descent?

Any thoughts on all of this or any other advice? (other than to move to Arizona)

hot_rod

What is the square footage?
A class 1 SIM is around 125 btu/ sq ft

Class 1 isn’t intended to keep up with a snowfalls , but to melt completely after the snow stops

It depends on how much snow and how quickly you want it gone

Critical applications can be well over 200 btu/ sq ft and those typically idle

Some additional info on the snow free area ratio

https://ratheassociates.zohodesk.com/portal/en/kb/articles/how-many-btu-s-do-i-need-for-snow-melt

yellowdog

I don't think a water heater is going to do much for a 475,000 btu snowmelt system.

mike99

That site was extremely helpful. I’ve known that I want the steep part to get more btu’s but to put a ratio on it makes sense.

The total for the entire driveway is around 3,000. However the plan, in my mind has been to keep the steep 100’ long portion accessible. Even if only by tire tracks. I just have to be able to get down it at 4am some times. While the rest is just to help clear off ice that sticks around too long.

As for water heaters vs a boiler. I agree a 199k tagaki will not do enough btu’s but that is why I question the 40gpm calculation. I’m wondering why my driveway isn’t able to function like two of Chris deckers. With multiple units cascaded.

GGross

It looks about right. Hopefully the person who designed it is going to actually install the specified 2" copper manifolds though. I tend to see these on the design and then they swap them out for brass or stainless on install adding to the pumping requirement. Personally I try to keep the pumping requirements down with shorter loops and multiple manifolds with their own supply/return, it may add some to the install to run extra pipes out from the mechanical room, but if you can use 2 pumps that are on the shelf at the supply house I think that is generally better than a single pump that might take 3 weeks to get if it fails

While it is possible to do this with a "water heater" I think you will find a 500,000 BTU/hr 95% efficient water heater costs significantly more than $1500 lol, in fact probably more than the boiler that you have picked out and it won't work as well or last as long.

mike99

Great point on sticking with off the shelf stuff.

Could you explain to me the difference to the fluid itself between one $18k boiler rated at 600k btu and 3 199k tagakis? From my reading they are designed for heat, and cascade so that when 600k is needed they accomplish that.

I’m just not understanding why a single boiler wins that challenge versus keeping $13k in the bank.

GGross

one thing that often gets overlooked with the tankless is that they are NOT in fact designed for space heating, most go so far as to require they are not used as strictly a space heating device. This is due to the design of the heat exchangers which are designed to function on higher pressures with a really wide delta T and 30-50 f fresh water on the "return". Takagi is one that specifically prohibits them from being used as a space heating only appliance, some don't state this because they want to sell you the water heater, and then sell you more in a few years. I'm not sure where your price comes from on that boiler, but I imagine its from an installer, ask them if they will install your 3 tankless heaters you bought yourself. My guess is that they will still need to make the same amount of money and you will pay for it one way or another. They also don't allow glycol...


From Takagi's manual



You do bring up an interesting point though, why a single 600k boiler if the cost is so high, versus 3 smaller bolers? you may want to discuss that with whoever gave you the price. Generally we are only allowed to discuss publicly available pricing on this forum btw.

hot_rod

A copper tube boiler might be an option

Zman

At 21% grade, you ARE a ski resort! How did that happen? 8% is code in most areas and >12% is pretty scary to drive unless it is completely dry. There is a risk of the driveway topping sliding and it would be a good idea to key it into the earth regardless of the insulation.

The GPM requirement is a function of the BTU's you are trying to deliver. BTU=GPM*Delta T*500(ish, depending on glycol). A typical snowmelt system for a residential driveway would use a delta T of 20 and a required output of 125 BTU/ft. 3,000*125=375,000 with a flow rate of 37.5 GPM. For a driveway like yours, it might be a good idea to zone the steep part separately because it will need to melt anytime there is snow present where the remaining driveway will be more forgiving. A heated cutoff drain at the bottom of the steep pitch will help prevent a glacier from forming at the bottom.

As for the heat source, I don't love water heaters as boilers, but depending on the amount of usage, they sometimes make the budget work. Where is the system located? Is the altitude deration for the boiler size a consideration?

hot_rod

Zman brings up a critical point with steep driveways, how to deal with the melt water at the bottom. It needs to pipe to a storm drain or run away somewhere where it doesn't create a wall of ice. Sometimes you need to heat the culvert also to assure the water gets away.

The road crew snow plows hate hitting a wall of ice in the highway.

I haven't had good luck with melting just the tire tracks. At the very least tube the entire drive, mark the tire track loops and try that first. But leave the option to melt the entire area.

WMno57

How many inches of snow do you get a year?
Any way to re-grade or re-route the existing driveway?
Detached garage up near the road an option? I see that a lot in homes near A-Basin and Alta.

yellowdog

3 boilers (not water heaters) would only be my choice if they are cheaper to buy and install over a single larger boiler. Once that snow sensor turns on the boiler, they will have to run full power to melt snow eliminating any cascading.

mike99

Wow.. This forum is incredible. Thank you for all the great feedback as it's been very helpful.

GGross,
Thanks for pointing me to the specifics of the tagaki units. I just got off the phone with their tech support and it was confirmed that I’d need to run any of their heaters through a heat exchanger. Beyond that, zero warranty although they know tons of people use them for heating alone as you stated.

Hot_rod,
I’ll look up copper tube boilers. Thanks

Thanks for the feedback on melting tiretracks. I’ll have the plan adjusted to ensure we have more btu’s going to the first tire track.

Zman,
I think I said it incorrectly. According to a fancy iphone app it’s 12 degree angle, 21%, or 1:4.7. Steep enough to make a 3/4 ton go about what felt like 20mph with your foot on the brakes. Not bad with snow tires but still a pain.

Thanks for the reference to keying it in. I had found that via google and it sounds like a no-brainer. I was even thinking I could have the helical pier folks drop a few in down the step part to secure the rebar too. Maybe that is overkill.

For the logic of having a different zone, I 100% agree and hope it can knock down my boiler requirement. I really need even a single tire track to be free from Ice to be safe. The rest would just be turned on when we have people coming over or it’s been too cold for ice to melt for a while.

Thankfully the entire driveway slopes down and right. All the water gets off the driveway and goes into a drainage ditch.

We’re in utah at 4,600 ft. I’m assuming that was taken into account in the planning.


WMno57,
It varies between a couple hundred inches and 400. However it’s really irrelevent often as the temps melt off most of the driveway within a week most times.

It’s about the most logical path for the driveway that I can get out of the lot unfortunately. It’s not bad enough to need a walk to the road. Just more convenient if we have good traction for the 80ish feet of steep.

Yellowdog,
I’m with you the multiple small boilers. From what I’ve read, it would even allow for one to fail and the other two to keep going. That redundancy seems like a no brainer even if the price is the same.

Zman

I'd take a look at a Lochinvar WHB 399. They test these at 9,600' and have them dialed in so there would be no altitude derate for your place. If you did the 100' of steep as a priority zone it would melt quickly. You could then use the remaining firepower to melt off the rest at a slower pace.

Zman

I am guessing that your phone app is a little off. 21% would mean that it rises 21' over that 100' section. I have seen a few that steep but not many...