Floor Heat Circulation Pump

One of the things we enjoyed the most about our old motorhome, was the radiant in-floor heating. There's nothing nicer than getting up on a cold morning and stepping out of bed onto a toasty warm floor. It just sets the day off on a good note. So when we designed our truck, we wanted the same "luxury" as the motorhome when it came to the floor heat. The difference this time is that the heat would be from the boiler system, instead of electric like in the motorhome. It meant we could have warm feet even if we weren't plugged in at an RV park.

In the motorhome, the entire coach could be heated solely with the electric radiant in-floor heat, so it was absolutely quiet. No sound from fans blowing air past a boiler powered heat exchanger. So we expected we could do the same with the truck. Unfortunately, we weren't expecting the contribution from the builder's "engineer". In other words, a radiant floor heat solution that was a complete failure. Not to mention a forced air heating system that took forever to heat the truck up to a comfortable temperature in the winter time.

Simple Laws of Physics

What never ceases to amaze us, is just how out of touch the builder’s engineer was with the most basic of engineering principles. The simplest of which is that everything in the universe follows the path of least resistance. The way this affected our radiant floor heat was really very simple. All the BTUs for both the radiant floor circuit and the forced air heating circuit came from the boilers. In other words, one source feeding both circuits through a Y in the plumbing. Logic has it that if both circuits were identical in every possible manner, then the fluid in the system would divide equally to both circuits at the point of the Y. But the two circuits were far from identical.

The radiant floor circuit consisted of around 80 feet of 3/8" diameter tubing, with as many as fifteen 180º bends. The forced air heat circuit consisted of about 16 feet of 3/4" tubing with only a couple of bends, AND it had an electric pump to help move the fluid through that circuit. 3/4" tubing has four times the cross-sectional area of 3/8" tubing and therefore one quarter of the resistance. You don't have to be a rocket scientist to figure out which way the fluid will flow.

When I was trying to explain to the engineer that the floor heat didn't work properly and why, his response was a blank stare of bewilderment. This is the individual that was responsible for every technical aspect of our build. A worrisome thought indeed.

A Working Solution At Last

It was only after I insisted that they provide us with another pump, and I plumbed it into the the radiant floor heat circuit myself, that our floor heating finally started working in the manner which we expected. Before I installed the pump, it took well over an hour of constant running before one could feel any warmth in the floor at all. After the pump was installed, the floor was warm in only about ten minutes.

We also supplemented the forced air heat circuit by installing a second forced air heat exchanger in the front living area, blowing towards the front of the cabin. Now with two operational boilers, a robust forced air heating circuit and fully functional floor heat, we should be nice and toasty, even if we're crazy enough to drive to Canada's northern arctic coast in winter.