brian haitz

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since Feb 19, 2017
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Recent posts by brian haitz

Skandi Rogers wrote:What is the heating at the moment? I would think the quickest way to guess how many kW you need is to see how many you are using at the moment. For example we have a 30kW output pellet boiler that runs around 30% most of the time so our house takes 10kW to heat with the outside at 0 and the inside at 20 using a mix of radiators and underfloor heating. However to heat the house downstairs (175m) from cold takes all 30kW for 4-5 hours.  we have poor insulation and a lot of heat loss from badly insulated pipes between the boiler and house, but also have south facing windows which help a lot, IF the sun shines  Your heating needs to be sized for the worst case so after a week of overcast weather at -6. my fear with a 5kw system is that from cold which it will be every time you let the fire go out for more than a day it's going to take you 6-7 hours to reheat the air and even longer to reheat the mass.

The official way to calculate is very complicated you need to know the R value of all walls roofs and windows which in practice is impossible to find on an old house especially if it's been retrofitted with insulation. I can find estimates online especially if you look at air to air heat pumps they estimate that a new/well insulated house requires 55w per m3 so guessing your house is 2.5m tall inside you would need 13kW to heat it.

heating has been wood stoves so far, but its been out of use for almost ten years so i've no data to go by. i'm guessing people were simply very cold-tolerant. :-D what i'm getting from you is that 5kw might be marginal and i tend to have the same feeling. especially since the oven is meant to server various purposes. i'm looking at the B28 batchbox from uzume at the moment, which gives more than 8kw from two firings.
what would the disadvantegs of a bigger system be? i'm struggling to see it, other than size and space isnt an issue in our case. bigger simply means i have to fire it less often right?

how does the theory work in terms of how much mass is ideal? is it a simple trade off of direct heat vs stored heat? in other words, what speaks against adding more and more mass, other than the obvious fact it takes longer for the heat to dissipate into the living areas.

and whats the general knowledge on convection heat (hypocaust) vs radiation heat (like hot water panels in the walls)? i'm assuimg in a well insulated house, it makes little difference. what about older badly insulated houses, is it generally a bad idea to convection heat such a house, i.e. wasteful and expensive? in my case the convection heat would go to the top floor, newly built and well insulated rooms. or is it likely more efficient and cheaper to install wall heating via hot water and radiate the heat.

thanks a lot!

1 month ago
hi guys,

been into rmh for a while and have a little experience with cob ovens. however thats not much good to me with this project as its quite ambitious. i'm looking to heat around 100m2 in this house via a central batchbox mass oven, with warm air ventilation to the rooms plus a small copper tubing hot water system for underfloor heating of a very small, but important space - the kitchen.

the oven will be located where the old roof meets the new flat roof and i'm guessing its gonna require some power. the house has been insulated recently but part of the floor will remain uninsulated, at least for the medium term, so there is heat loss to consider, but not from the roofs or the room where the oven will. still the oven needs to:

- radiant heat the room its in, very high 65m3 room
- warm air vent 3 rooms, ca. 100m3
- hot water underfloor heat a 25m3 room

winter lows are -6 at max. with many sun hours, and the south facing windows collect considerable amount of warmth which is stored in a 2 inch thick cob wall on the northern side. i have a bunch of very capable builders with me, so i'm hoping to save on costs by doing the construction myself.

one general question i have is how do oven builders calculate the required power output for a certain amount of m3 space?

well, the options i'm seeing right now are:

Uzume B14

seem to do great work. obvious advantage is the black baking oven. but i have doubts over the power output being enough? they dont offer a copper tubed hot water system, so the question would be how tricky it would be a add that myself, or have someone add it. also if i chose this, would i be well advised to sacrifice the bench in order to give more power to the other functions?

sent me info on their modell BrulR 1.5 which is a rocket batch box side winder with heatriser, diameter 150mm. 5KW and 93% efficiency. he offers an integrated copper tubed hot water system for underfloor heating in 3 sizes, of which i'm assuming the smallest would suffice. only disadvantages are the lack of a baking oven and a bench.

Hire someone else to make a design:

well, seeing as there will be some level of adaptation / individual design i'm gonna be paying some to help creat plans anyway. what would your advice be? and what options am i missing? what considerations am i missing?

how do you guys, in europe, see the development of governmental regulations on wood stoves? dont really feel like building an amazing 5 grand oven thatll be forced out of order in 10years. or would that be an argument for a prefabricated oven with very good exhaust specifications?

thank you all for your great work - more power to you!


1 month ago

i've built a rmh and a double chamber cob oven before but i'm no expert.

for a major renovation of our house we are planning on building a large central rmh/wood oven to heat a small two storey house. we're looking at options of including underfloor heating/hot water and/or pizza oven in the plans. so yes.. its quite ambitious. the underfloor heating and hot water (for feeding wall heating panels is priority. so i need advice and am happy to pay for it (or make you a website!

anybody know of rmh builders/consultants or oven builders with some experience in rmh in central europe, so france/germany/netherlands/switzerland?

thanks for your help and best wishes!

9 months ago

i'm looking at buying/renting sth like 2 acres of grazing land to keep sheep and plant some fruit trees.

is there a "beginners guide" book or thread you could recommend? can someone give me some base data like.. how roundabout how many sheep make sense per acre, races of sheep (primarily for meat and ease of keep).

anybody living in france know about beaurocratic requirements and costs involved?

thanks everybody!! kind regards,

Hello Erica,

Thank you loads for your reply, it's great to get the assertion from you guys directly! Highly appreciated and I would love to join one of your workshops if it wasn't for the distance < maybe there will be one in Europe one day.

So we went ahead and built the oven with 1 inch of thermal Mass and unfortunately as it was my first time building something like this I made all the mistakes you can imagine. The most crucial one being that I didn't get the mixture right for the thermal mass, It was too wet and therefore kept slumping and the whole thing just didn't go very well. I decided to mark it down as experience and make another oven and given the second opportunity I decided I will try to build a slightly lower oven to favour Pizzas. This time the mixture felt really good and the build went very well. The ratio of sand to clay was about 4/1 and as it dried out there were no cracks and the thermal mass dome looked Great so I was quite confident. As my daughter's birthday came up I thought I can use the oven the way is and add the rest of the installation later. Sadly now after three firings the thermal lining has developed a lot of fine cracks and even one larger one which is about a 10th of an inch. Is it possible that I fired the oven too hot? I am a bit surprised since all the tests of the mix went well and there were no cracks whatsoever after completely drying the thermal lining. The insulation had not dried out completely before firing so could that have caused the cracking? the inner lining however worked great in terms of efficiency. We got the oven to 350 Celsius in under an hour , baked 4 great pizzas and even with the thin installation we have at the moment we had no problem baking one round of breads afterwards. After that the oven still measured 130° Celsius

Would there be at any point in trying to remove the installation layer and patch the thermal lining from both sides or is this oven going to have to come down?

Obviously very disappointed but thanks again for all your help and advice!
3 years ago
Hi folks,

We have a beautiful Black Mulberry tree and harvest time is coming up soon and we have tried out various ways of harvesting the berries in the last couple of years. I was wondering what kind of setups you people have come up with to harvest the gorgeous but fragile fruits. Our best solution so far have been 2 huge elastic bedsheets elevated by four sticks each in the ground, it reduces the falling height and softens the land and it keeps the berries off the ground. Another bonus is you can let them ripen and Fall in their own time.

I will try and think of making a photo of our setup
3 years ago
what mushroom is this?  just popping up everywhere in the garden , I'm assuming it's non edible but I'm curious
3 years ago
Hi guys,

I have never been much of a reader, but after the arrival of my daughter I have been given presents of 2 parenting books which I both really enjoyed in terms of the insights into the world that children live in and of course it is just worth it for the good advise you pick up here and there.

Anyone have some favourite parenting books they can recommend? we like Montessori for example

3 years ago
Hi guys,

I have built an outside earthen oven, as in the double chamber oven, And Im contemplating various ways of protecting it from the weather. One idea I liked was to simply cover it rather than build a roof which takes up quite some space. However, The main argument against doubts is that's it simply isn't pretty to look at a plastic sheet all year round rather than the beautiful oven you built.

I would be prepared to use proper roof tiles but I don't want to build a structure that can support them. That would mean a lot of foundation work and equally take up a lot of space. I am looking for a solution that is lighter, Like sheet metal . I don't like tar paper.

Can anybody imagine a type of roofing, possibly even involving some natural materials (as in unprocessed). Obviously it needs to be water repelling, Strong enough to withstand strong rain, if possible not too susceptible to Wind and not easily flammable, However the roof Will be quite high and further precautionary steps would be possible to make something heat resistant. The only obvious types of natural roofing I can think of is Thatching, Which obviously is not to suitable over an oven.

Happy for any suggestions.
3 years ago
Hi guys, a couple of questions as we are going to build this oven soon, according tothe plans.

1 Considering the re-burn going into the exhaust pipe, does the pipe need to be stainless steel or will a copper pipe stand the heat?

2 I would like to tune the oven to heat up faster and cool down faster so it suits our small family needs better. To bake about two pizzas and one bread Will take about an hour and a half of baking time or a little less. Do you think an inch of thermal mass should be about right for that or will I risk it's cooling down too fast? I have obtained Chamotte Stones an inch thick for the base to go with it. Also what would you recommend as maximum installation thickness for such a setup?

3 in the book you mention that the exterior may not be treated in a way that the oven cannot breathe. How does simply linseed oiling it fair in that respect? Does that also inhibit breathability? And does polishing the exterior clay make a difference?

Thanks a lot!
3 years ago