Takagi Heaters for Snowmelt?

Rob Blair

I agree that we normally shoot for 100 BTU per square foot. Like I said, we came up with 10" oc, 300 foot loops of 3/4" and at the design of 289K that the 368K net NTI will have a little above the design. Knock on wood, have not had any problems yet. Definitely do not want to undersize.

Rob

Rob Blair

Takagi Heaters for Snowmelt?

Saw a bid on a 4000 square foot snowmelt in which the guy specified a Takagi TK2 waterheater. I was going for something in the 300-400KBTU range. Am I way off? Are these Takagis that mighty?

Rob

Glenn Sossin_2

NO GOOD

WRONG WRONG WRONG This unit has a max input of 185,000. Based on the size of the driveway you mention, your probably looking a load of around 450,000 to 500,000 or more depending on design conditions. The maximum flow rate though the heat exchanger on this unit is just under 7 gpm. You probably will have a system flow rate between 35 and 45 gpm, again based on system design factors.

The wall hung heaters are designed with very small heat exchangers that require high head pressures - the water main provides that - 40,50 60 psi or more. The minimum inlet pressure for this unit is 15psi. That means your starting out of the box with almost 35 ft of head before you even look at the system piping - typically in the 15-25ft range. You are well beyond the range of the most common circulators that would normally be used.

You should be looking at condensing boilers. They would be like pac man in this type of system. You would achieve the highest levels of efficiency (on the combustion side).

I have used a Takagi in a snowmelt system before. It was a small boiler room, it was 1 of 2 boilers piped in a primary secondary system with a plate exchanger for the snowmelt side. It worked but I did not get the full btu rating out of the Takagi. I checked the flow rate through the heater. With a total of about 10ft of 3/4 copper, and a UP26-99f, I believe I was getting around 3 gpm through the unit. Live & Learn.

I recently did another snow system, slightly smaller in size than the one your describing. I used 2 Prestige PS-250 boilers with a Tekmar 665. Worked perfectly. The calcultions have to be done properly. Clearly the person who made this other bid had little experience with snowmelt and product selection. If he gets the job, theres going to be one unhappy homeowner outhere.

Rob Blair

Thanks Glenn. My rep did a heatloss for the snowmelt and came up with 289Kbtu with a 30 degree delta T. I have installed others that he did the calcs and they worked fine. I was planning on a Tekmar 664 with the slab sensor and an NTI Ti400 for the heat.

Thanks,

Rob

Glenn Sossin_2

Still seems to be on the low side to me

You stated your rep came up with 289,000 btu's. Are we talking net load numbers or input of appliance numbers. Secondly, even if we figure that these are net numbers, for a 4,000 sqft driveway, that would be approx 72 btu's persqft. Better insulate that driveway well.

This seems very low to me. The 30 degree delta T reduces your gpm requirement to around 19 gpm but this is still well outside the range of even 2 of the Takagi units. Glad to see your using a larger condensing boiler instead.

Typically, we will design to a load of approximately 120 -150 btu's persqft here on LI. The actual load calculaton depends on the customers expectations and the site/constuction conditions.

When someone is spending 30,40,50k or more for the driveway, they expect to melt the snow. With the boiler you mention, and a 4,000 sqft driveway (unknown construction / insulation / location), you are close to the capacity edge. Don't fall off.

Good luck

Glenn

Troy_3

Snowmelt

We design snowmelt between 125-150BTU/sq.ft. 300' 3/4" pex loops works well. 3/4" PAP will even give you a little better flow. 9"oc. Rememeber to size your piping and pumps for 60deg.glycol. It takes more push than 180deg. water. Condensing boiler all the way.