Feasibility of solar hot water for New England home with radiant floors

grwa

We're in the Boston suburbs area in MA. We didn't quite know what we were getting into with the HVAC system when we purchased our ~5900 sqft home. The HVAC was installed in 2006. It includes both a hydronic 2-pipe system with summer/winter switch and 12+ air handlers, as well as radiant floors. All of the heating (for 2-pipe system, radiant floors, and domestic hot water) is supplied with two oil boilers.

The home has two stories and a basement. The first floor has combined 75,000 btu/hr radiant floors. The second floor, as far as I can tell, has radiant floors in the master bathroom and nowhere else. However, the HVAC plans show radiant floors also in the master closet and bedroom. (The bedroom and closet have wood floors, so this seems unlikely.) The plans show 8000 btu/hr for the bathroom, 2000 btu/hr for closet, and 10,000 btu/hr for master bedroom.

Currently, we have switched the hydronic 2-pipe system off (this saves electricity massively, since the system requires a 1500HP Bell and Gossett circulating pump to always be on). So far, this winter hasn't been very cold, and the first floor radiant has been enough to keep the house warm. (The second floor radiant heat appears not to work unless the 2-pipe system with circulating pumps are on.)

Searching on heatinghelp.com, I recently came across the website of a local plumber/hvac technician/contractor/specialist. His website shows pictures and description of a solar thermal system (Thermomaxx evacuated tubes) he's installed for his own New England home. It seems that he has been able to generate enough hot water for radiant heat and domestic hot water that he could keep his oil boilers off even in late December.

Question 1
Could we feasibly do something like this for our radiant floors, at least on the first floor? We have plenty of roof space with decent sun. Our roof is basically a flat roof with ~7 degrees pitch. We could consider south-facing ground-mounted solar collectors too. We don't really have an attic, but we have enough space in the basement for large water tanks.

But could we generate enough hot water in the winter time for the amount of hot water we need for 75000 btu/hour radiant floors? Or what percentage could we generate, at least preheating the water?

Question 2
If the system is technically feasible, how possible is it to find an installer? Would this have to be a DIY project? Is solar hot water (in our area, at least) "dead"?

We've gotten a few solar PV quotes, but overall, I've gotten the idea from HVAC experts I've spoken with that electric resistive heating to run our radiant floors would be impractical.

Thanks in advance.

Hot_water_fan

Yikes! I'd skip solar thermal entirely - too niche and expensive. Look at heat pumps - you can use air-to-water for the radiant floors (they work great for low temperature applications) and/or air-to-air options for the air handlers. This will also handle air conditioning. It would cost about 2/3rds less to operate than electric resistance.

If the system is technically feasible, how possible is it to find an installer? Would this have to be a DIY project? Is solar hot water (in our area, at least) "dead"?

People have different definitions of "dead" but yes, it's very rare and has been outperformed by solar PV for at least a decade. It's a LOT of complexity for something that's not very valuable.

But could we generate enough hot water in the winter time for the amount of hot water we need for 75000 btu/hour radiant floors? Or what percentage could we generate, at least preheating the water?

The 75kbtu number is just a guess your original installer came up with. How much oil did you use last year?

hot_rod

At best you could cover 40% or so of your DHW load with 3 collectors. That would be the better load as it is year around. You are not in a great area for solar thermal heating. Too cold, not a lot of winter sun.

The very best place to upgrade is the building evnvelop. Make sure you hav e plenty of insulation. All; cracks around foundation sealed well. Possibly you would get an energy audit that would include a blower door test.

Many states and utilities have weatherization funds available. Check www.dsireusa.org for programs.

Mad Dog_2

As the others said...when done diligently & properly, it works nicely as a healthy supplement and contributor to your domestic hot water & radiant needs, but don't expect miracles.  Mad Dog 🐕