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Our Energy Engineer on Heating Systems and Insulation

Recently, one of our customers sent us this note:

“When you were speaking yesterday, it rang a bell with something that I had read about online. Radiantec recommends a different H2O tank and 7/8″ tubing for slab on grade. If you get a chance would you mind perusing this product and their suggestions and give me your thoughts/experience/recommendations?”

The following response is from David Posluszny, an Energy Engineer at Dolphin who built a net-zero home in Massachusetts:

“Radiantec has some great products and information on their website.

Tube size: There is nothing wrong with installing a larger size. 1/2 inch is the minimum I would use, but you can always go larger.

The Polaris water heater uses Fossil fuels to make a flame. I don’t think anyone should have flames in their homes because of risk and maintenance. But, in addition to that, let’s look at heating load. The smallest Polaris water heater costs $3,200 and puts out 100,000 BTU/hr. If your home required 100,000 BTU for its design load, then we may consider this. However, it is a lot of BTU’s. My home (insulated with dense-pack cellulose) has a design load of 4,000 BTU/hr. A life-time guaranteed electric tank will cost about $1,000 and put out 15,358 BTU. So why spend the additional $2,200 for an over-sized tank that will require maintenance, and eventual replacement? Also the Polaris tank requires hook-ups of fossil fuels (cost), to be contained in a CAZ room (cost), and an exhaust port to the outside (cost and penetration losing heat). None of those additional costs are required with an electric tank.

I recommend the Rheem, Marathon tank. Simple, clean, no sound, no maintenance, and you can put it anywhere inside your home without having to meet special fire codes. If you use it for both taps, and heating then choose a large model (80+ gallons). If you want to have two tanks, one for heating, and a separate one for taps, then the heating one can be small (40 gallons). There are pros and cons to both ways which will require a more lengthy conversation.

Here is the formula: $X = (Heating system + Insulation). In my home I chose to spend my money on the insulation, and I kept my heating system cost extremely low, ($80). But to make a house warm with an inexpensive heating system, the house as a system requires the insulation be installed perfectly. Likewise, if you skimp on the insulation, you will have more heat loss, and thus require a more expensive heating system.”