stove with backboiler for mhrv

selfbuildsoon

Does anyone have a stove with a backboiler for use in an airtight house with mhrv that they'd recommend? It's a minefield!
Also, when putting in the pipes for the external air supply; how are they finished outside?Thanks

kieranhr

selfbuildsoon wrote: »

Does anyone have a stove with a backboiler for use in an airtight house with mhrv that they'd recommend? It's a minefield!
Also, when putting in the pipes for the external air supply; how are they finished outside?Thanks

I'm open to contradiction, but pretty much any room-sealed stove with an external air supply is fine for MHRV. You'll find about a dozen stove suppliers from a google search. I'm not sure if I'm allowed recommend any here. (?)

The external air supply duct should be about 125 mm diameter, unless you have a specific stove in mind, in which case go with the manufacturer's recommendation. Ideally the stove would be on an external wall, in which case I usually duct the air supply straight out the back and finish with a vent cover about 500 mm above ground level. If it's on an internal wall, you have to duct through the floor slab, but try finish it at least 150 mm above ground level by cranking it up the wall.

CotBC

I have a stove with a backboiler installed. It's on an external wall with the air intake generally as kieranhr described.
While there are any number of stoves available, having a backboiler included does really narrow the options. The one I have is a 15kW unit, with 10kW to water and 5kW to room (and even that is too much to the 5.5m x 4.5m room after a few hours burning!). Mixed results with the backboiler to be honest. It feeds into the bottom of a 750l thermal store, and it takes about 4hrs to raise the middle of the tank by approx. 10C ... better than nothing, but generally not enough to avoid having the oil kick in during the winter months to get the water to the required temperatures.

kieranhr

Thanks for the feedback CotBC, interesting stuff. I'm not a fan of back-boilers to stoves at all. Much cheaper and more efficient to heat domestic hot water with a timber pellet boiler, say.

CotBC

Yes, I looked at the wood pellet option at the time (2009), but there was a lot of negative press about the poor quality of the pellets available, so that in combination with the large hopper requirements put me off. I did however leave myself the option to swap out the oil boiler in the future if it appears to be a cost effective option.
On my own backboiler, our thought process was that since we were putting the investment into a stove and firewood anyway (just need the fire effect on those winter evenings ), we figured why not try to get the extra bang for the buck by adding the boiler and using it to boost the storage tank.
I should clarify that since my tank is located in the garage, there is a run of several meters between the boiler and the tank, and because we were forced to use copper piping, we could not get anywhere near the level of insulation I would have liked, so there is certainly some heat loss involved. That is mitigated by using more complex controls for the circulation pump, but that in combination with over-temp and over-pressure valves made the whole thing quite a headache to install and fine tune in operation. Would be much easier if you have gravity feed from a tank in the hot press!